Polycyclic aromatic hydrocarbons (PAHs) are hydrophobic aromatic compounds consisting of two or more condensed benzene rings, having greater teratogenicity, carcinogenicity, mutagenicity and toxicity. The most representative PAHs is benzo(a)pyrene (B[a]p), which is composed of five benzene rings, and is classified as a Group I carcinogen. The treatment technologies for B[a]p removal include bioremediation, physical remediation and chemical remediation. The advanced oxidation technology based on sulfate radicals becomes a recent research hotspot because of its high redox potential, high reactivity and environmental friendliness. Nevertheless, persulfate needs to be activated through various approaches to produce a series of reactive species, and iron-based materials are widely used due to the abundant reserves, environmental friendliness and excellent activation performance. In this paper, pyrite (FeS₂) was used as a cheap and non-toxic sulfide mineral, allowing for a slow release of Fe²⁺ as well as the cycling of Fe²⁺ and Fe³⁺. Kaolinite was chosen as a suitable carrier to solve the agglomeration of FeS₂ nanoparticles. A composite with FeS₂ and kaolinite was prepared to obtain efficient persulfate activation and B[a]p degradation.

Ferrous sulfate heptahydrate (FeSO₄·7H₂O), sodium thiosulfate (Na₂S₂O₃), cetyltrimethylammonium bromide and kaolinite were ultrasonically mixed and stirred for 30 min, and then the solution was transferred to a reactor for the hydrothermal reaction. At the end of the reaction, the solution was centrifuged and washed for three times, and then put into a vacuum oven for 12 h to obtain the composite catalyst.

The B[a]p solution, desired dosage of catalysts and peroxymonosulfate (PMS) solution were added in a centrifuge tube of 50.00 mL, and then conducted in a rotating mixer at room temperature. Before adding PMS solution, the adsorption-desorption equilibrium process was carried out under 30 min continuous stirring. Moreover, 1.00 mL of the mixture was taken at the setting time points and quenched with 0.50 mL of MeOH. Finally, the mixture was analyzed by high-performance liquid chromatography (HPLC) after filtration.

Also, 4.00 g B[a]p-contaminated soil, desired dosage of catalysts and PMS were added in a centrifuge tube of 50.00 mL, and then conducted in a rotating mixer for 60 min at room temperature. After 60 min reaction, the supernatant was poured after centrifugation, and then the soil sample with an extraction fluid (MeOH and acetonitrile in a volume ratio of 1∶1) was ultrasonicated for 60 min to obtain 20.00 mL of soil extract. Finally, the supernatant was withdrawn and filtered for HPLC to test the residual B[a]p concentration in soil samples after centrifugation.

According to the analysis by scanning electron microscopy and energy dispersive spectroscopy, a composite with kaolinite and layered FeS₂, can be prepared. The specific surface area of FeS₂/kaolinite slightly increases, and the particle size of FeS₂/kaolinite is smaller than that of FeS₂, which is attributed to the elimation of the agglomeration via the introduction of kaolinite and the improvement of the dispersibility of FeS₂, resulting in the superior catalytic performance for PMS activation and B[a]p removal.

The results show that the B[a]p removal rate is 93.00% (liquid-phase) and 69.02% (soil) under the optimum conditions (i.e., 2.0 g/L catalyst, 20 mg/L B[a]p concentration, 2 mmol/L PMS concentration (liquid-phase) and 50 mg/g catalyst, 80 mg/g PMS, 3∶1 water/soil ratio (in mass), respectively). The acidic and neutral conditions are more suitable for the PMS activation and B[a]p removal. Also, the B[a]p removal is affected in the presence of H₂PO₄^2- and HCO₃^-. The existence of Cl^- and NO₃^- promotes the B[a]p degradation efficiency. Based on the quenching experiments, the reactive species including ¹O₂, SO₄^•- and O₂^•- are proved to be involved in the process of PMS activation and B[a]p degradation, and ¹O₂ and O₂^•- are further confirmed to be the dominant reactive species.

Based on the mechanism of PMS activation in FeS₂/kaolinite/PMS, the content of Fe²⁺, S₂^2- and S⁰ is decreased after the catalytic reaction, indicating that Fe²⁺ is the main driving force for the PMS activation to generate ¹O₂, SO₄^•- and O₂^•-, and the cycling of Fe²⁺ and Fe³⁺ is facilitated in the presence of S₂^2- and S⁰ possessing reductivity. In addition, the oxygen-containing functional groups contained in kaolinite can be also beneficial to the PMS activation.

A composite of FeS₂/kaolinite was synthesized by an one-step hydrothermal method for PMS activation and B[a]p degradation. The degradation results demonstrated that 93.00% B[a]p was removed within 15 min under the optimized conditions (i.e., 2.0 g/L FeS₂/kaolinite, 20 mg/L B[a]p concentration, and 2 mmol/L PMS concentration). ¹O₂ and O₂^•- played a dominant role in FeS₂/kaolinite/PMS for PMS activation and B[a]p degradation. The excellent catalytic performance of FeS₂/kaolinite was also confirmed in the degradation experiment of B[a]p removal in soil, with 69.02% B[a]p degradation efficiency under the optimized conditions (i.e., 50 mg/g FeS₂/kaolinite, 80 mg/g PMS, 3∶1 water/soil ratio and pH value 3). The high catalytic performance of FeS₂/kaolinite was mainly due to the cycling of Fe²⁺ and Fe³⁺ as well as the reduction reaction between Fe³⁺ and S₂^2-/S⁰.

Eutrophication becomes more serious with the development of society. It is difficult for the conventional sewage treatment technology to meet the requirements of environmental treatment. Efficient and economical deep nitrogen and phosphorus removal technology becomes a necessity. Biological method is often used for nitrogen removal, and physicochemical method is effective for phosphorus removal. The technology of biological denitrification for nitrogen removal is mature and widely used. For phosphorus removal, chemical precipitation usually requires additional structures and may cause secondary pollution. Physical adsorption has some disadvantages of low saturated adsorption capacity and high cost. Therefore, the potential application of some industrial solid and mineral wastes with high activity, low cost and environmental friendliness has attracted recent attentions. The development of phosphorus removal materials based on solid waste is a current research hotspot. Compared with the conventional physicochemical method, the crystallization method can reduce the structure and facilitate the recovery of phosphorus. Phosphate ore in China is rich, and the massive mine tailings after processing are piled up at will due to the improper development, resulting in environmental pollution and resource waste. Collophanite is in apatite, which can be used as a crystal seed of phosphorus removal by crystallization method. This way can reduce the cost, and realize the resource utilization of waste. In the early stage, low-grade collophanite as a mineral waste was used for deep phosphorus removal in sewage. This paper was to explore a possibility of simultaneous nitrogen and phosphorus removal in one reactor via physicochemical and biochemical processes. A low-grade collophanite was used as a denitrification filter, which acted as a carrier of denitrification microorganism attachment and growth and provided an apatite crystal seed. Effect of mineral fillers on the simultaneous nitrogen and phosphorus removal was investigated.

Low-grade collophanite, anhydrite and calcined magnesite coarser particles were crushed and classified into smaller particles with the sizes of 2-4 mm. A dynamic heterotrophic nitrogen removal column was constructed with low grade collophanite as a main component and anhydrite and calcined magnesite particles as fillers. The anaerobic sludge was cultured and enriched with heterotrophic denitrifying bacteria in a sewage treatment plant, and the heterotrophic denitrifying bacteria were inoculated for simultaneous nitrogen and phosphorus removal. The effluent nitrogen, phosphorus and other related indexes were monitored regularly to investigate the influence of combined mineral fillers on the nitrogen and phosphorus removal. The feasibility of simultaneous nitrogen and phosphorus removal with different combined filters based on low grade collophanite was verified. The microstructure of fillers, the morphology of minerals and the relationship between minerals and microorganisms were characterized by scanning electron microscopy, transmission electron microscopy and microbial community analysis.

The results show that the phosphorus removal is ineffective when low-grade collophanite is used as a filter because of insufficient calcium ions required for apatite crystallization. The addition of anhydrite to low grade collophanite can obtain efficient simultaneous nitrogen and phosphorus removal. The combined fillers of low-grade collophanite, anhydrite and calcined magnesite have a positive effect on simultaneous nitrogen and phosphorus removal. The effluent total nitrogen concentration is stable (i.e., below 3 mg/L) and the effluent phosphorus concentration is below 0.5 mg/L when the hydraulic retention time is greater than 1 h, meeting the Grade A discharge requirement (GB18918-2002).

The higher pH value is conducive to phosphorus removal, but has no significant inhibition on microbial denitrification and nitrogen removal. All the combined filters can be used as a carrier of heterotrophic nitrogen removal microorganisms, and there is little difference in nitrogen removal efficiency, compared with quartz sand.

The mechanism of efficient phosphorus removal by mineral combination is since anhydrite releases calcium ion and calcined magnesite releases hydroxyl to promote the growth of apatite when using collophanite as an apatite crystal seed. The existence of biofilm has a diaphragm effect on ion diffusion during apatite growth, and the phosphorus removal effect is not as good as that of sterile system.

Effective nitrogen and phosphorus removal in a single reactor was realized when anhydrite, calcined magnesite and low-grade collophanite as a main component of the filter materials were used. The results obtained could provide a promising potential for the resource utilization of low-grade collophanite as waste minerals.

In China, thousands of tons of highly toxic hexavalent Cr slags are produced annually. The existing remediation technologies face challenges due to the facile oxidation, "re-yellowing" effects, and contamination from iron additives, hindering the achievement of sustained governance and resource recycling for Cr pollution. This study conducted microbial mineralization experiments on soil at actual Cr-contaminated sites, delving into the stability, recyclability, and reaction mechanisms of mineralization products. The results indicate that this method can efficiently reduce Cr⁶⁺ and Fe³⁺ in Cr slag to form precipitates. After 60 d extensive air exposure, the mineralized products exhibited little reoxidation or re-decomposition, and demonstrated weak magnetism, indicating a potential for recovery by magnetic separation. This paper was to investigate a low-cost, efficient in-situ, and long-term governance solution for treatment of Cr pollution on-site and facilitation of the recovery and reuse of Cr resources.

Cr-contaminated soil samples were collected in Henan province, China. The pH value, total Cr, and total Fe concentrations of the soil were measured. Shewanella oneidensis MR-1 (S. MR-1) was cultured and acclimated to high concentrations of Cr⁶⁺ and alkaline conditions to enhance its reduction capabilities. In the microbial reduction experiments, S. MR-1 was added into Cr-contaminated soil at different concentrations of Cr⁶⁺, Cr³⁺, and Fe²⁺.

The microbial morphology and surface elemental composition of the samples were determined by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS). The microstructure of the samples was analyzed by transmission electron microscopy with energy dispersive X-ray spectroscopy (TEM-EDS). The concentrations of Cr⁶⁺ and Fe²⁺ were measured by ultraviolet-visible spectrophotometry (UV-Vis). The magnetic properties of the eaction products were characterized by vibrating sample Magnetometry (VSM). The Cr valence states before and after remediation were analyzed by X-ray photoelectron spectroscopy (XPS). The concentrations of Cr and Fe were determined by inductively coupled plasma emission spectroscopy (ICP).

The results show that S. MR-1 significantly reduces Cr⁶⁺ in the contaminated soi and the Cr⁶⁺ concentration decreases to detectable limits for 4 d treatment. Concurrently, the concentration of Cr³⁺ initially increases and then stabilizes, indicating the formation of stable Cr precipitates. The Fe²⁺ concentration increases after most of Cr⁶⁺ reduces, showing the simultaneous reduction of Fe³⁺ in the soil.

Based on the evaluation of the stability of the remediation products for 60 d, the treated soil has a minimal release of Cr³⁺ and no reoxidation to Cr⁶⁺, even when exposed to environmental conditions. This stability is attributed to the formation of stable mineral phases, which are confirmed by VSM and XPS.

The microbial reduction process results in the consumption of soil organic matter, which favors preventing the formation of soluble Cr³⁺ complexes that can be reoxidized. The mineralization control process of Cr-contaminated soil mediated by S. MR-1 can be divided into three stages, i.e., S. MR-1 decomposes soil organic matter, produces OH^-, creates an alkaline environment, and transfers the obtained electrons to the solution and Cr⁶⁺ and Fe³⁺ in the soil, generating Cr³⁺ and Fe²⁺; Microorganisms inhibit the binding of Cr³⁺ with organic matter, engage in ion exchange with the environment, and Fe³⁺, Cr³⁺, and Fe²⁺ are adsorbed on the cell surface or enter the cell body, forming stable minerals under the control of microorganisms, which belongs to the microbial-controlled mineralization mechanism. Microbial secretion of extracellular polymeric substances (EPS) regulates the surrounding environment to achieve mineral precipitation conditions, inducing the mineralization of Cr³⁺, Fe³⁺, and Fe²⁺, which belongs to the microbial-induced mineralization mechanism. The minerals generated in the solution due to their higher density than water deposit at the bottom of the solution, forming a black mineral layer; and S. MR-1 continuously decomposes organic matter in the soil, reducing excess Fe³⁺ to produce Fe²⁺ and maintaining a reducing environment.

This study introduced the use of the dissimilatory metal-reducing bacterium S. MR-1 for the treatment of substantial iron in the existing Cr-contaminated sites. The introduced microorganisms utilized soil organic matters to generate an alkaline environment favorable for mineralization. Within a short time frame, they reduced all Cr⁶⁺ to Cr³⁺ and some Fe³⁺ to Fe²⁺, thereby facilitating the controlled formation of stable phases of Cr³⁺, Fe³⁺, and Fe²⁺, intracellularly and extracellularly. The microbial treatment products exhibited the structural and valence state stability under prolonged oxidative conditions, preventing the release of Cr ions into the environment. Also, the product had a degree of magnetism, offering a cost-effective solution for subsequent resource recovery. This method could overcome the limitations of conventional microbial in-situ remediation technologies (i.e., extended treatment durations, intolerance to high Cr concentrations, and poor product stability). This work could address the challenge of unstable and easily re-oxidized products at Cr-contaminated sites, providing an economically viable solution for Cr pollution remediation in diverse environments, i.e., surface water, groundwater, and soil with varying pollution levels. Moreover, this work could give a basic foundation for low-cost Cr resource recovery.

Electrokinetic remediation is a promising method for Cr(VI) treatment. Electrokinetic remediation operates based on a low-intensity electric field across the soil, which mobilizes contaminants towards the electrodes. Some previous studies tried to improve the mobility and availability of contaminants for extraction. However, the technology faces some challenges such as interference from non-target contaminants. It is thus necessary to develop the electrokinetic remediation with other technologies like chemical agents and permeable reactive barriers. Some minerals can be used to remediate Cr(VI) due to their properties like surface effect and redox effect. The existing researches on minerals for Cr(VI) remediation mainly focus on zero-valent iron (ZVI) materials. ZVI usually requires loading materials to minimize agglomeration. In this paper, a magnetite/pyrrhotite composite material (i.e., pyrrhotite naturally dispersed in magnetite) was introduced to the electrokinetic remediation systems, mitigating shortage of electron donors in Cr(VI) contaminants and stabilizing Cr in the form of Cr-containing minerals. The impacts of mineral filling position and potential gradient on the Cr(VI) remediation performance were investigated, and the Cr-containing products were analyzed.

The mineral enhanced electro-remediation devices consisted of acrylic reactors (length 100 mm, diameter 50 mm), and plate-shaped electrodes (length 80 mm, width 50 mm). The minerals were filled on the both sides or in the middle. The applied potential gradient was 0.2 V/cm or 0.4 V/cm, provided by a model CHI 1000C Electrochemical workstation. In the remediation process, the samples were taken at 12, 24, 36, 48, 72, 96, 120, 144 h, and 168 h, respectively. The concentrations of Cr(VI) were determined by a model Thermo Fisher EVOLUTION 220 UV visible spectrophotometer based on the national standard GB7467-87. The total Cr (TCr) concentrations were determined by a model SPECTROBLUE SOP inductively coupled plasma optical emission spectrometer, in accordance with HJ 776-2015 method. The mineral phase was tested by a model PANalytical X-pert3 powder X-ray diffractometer (XRD), and the element analysis was performed on a model Thermo ARL ADVENT XP+X-ray fluorescence spectrometer (XRF). The scanning electron microscopy images and energy dispersive X-ray spectroscopy mapping of Cr-containing products were performed by a model FEI Quattro S environmental scanning electron microscope (ESEM) at 15 kV. The Raman spectra were determined on a model Renishaw inVia Reflex Laser micro-Raman spectrometer with a 532 nm laser. After remediation, the reaction devices were maintained at room temperature for six months. Subsequently, the contaminated simulated soil underwent a second washing with ultrapure water to mimic leaching of harmful components into the environment under specific conditions. The concentrations of Cr(VI) and TCr were measured to evaluate the stability of the remediation. The electrodes were removed from the devices, weighed, and placed in 250 mL beakers. The volume of leaching agent and water was determined at a liquid-to-solid ratio of 10∶1 (L/kg). After adding the leaching agent, the beakers were sealed with a film and mounted vertically in a horizontal oscillation device (THZ-D). The oscillation settings were adjusted to 120 cycles per minute with an amplitude of 40 mm. The leachates were then filtered through a 0.45 μm microporous membrane, collected and analyzed for Cr(VI) and TCr concentrations. This process assessed the contribution of electrodes adsorption to Cr(VI) removal, following the guidelines of HJ 557-2010.

The XRF and XRD analysis demonstrate that the minerals in magnetite/pyrrhotite composite are mainly composed of 70% magnetite and 26% pyrrhotite. Moreover, the mineral material does not contain other heavy metals. The mineral and electrokinetic remediation both are effective in the treatment of Cr(VI)-contaminated simulated soil. However, reducing the Cr(VI) concentration below 200 mg/L proves a challenge. In contrast, the mineral-enhanced electro-remediation system reduces the Cr(VI) concentration to 200 mg/L within 24 h and progressively approaches zero at seventh day. Also, the removal efficiency of Cr(VI) at both the anode and cathode doubles, compared to electrokinetic remediation. The effects of potential gradient and mineral filling position on the remediation of Cr(VI) were investigated. The results reveal that the experimental systems with a higher potential gradient exhibit the superior removal efficiency for TCr, compared to those with a lower potential gradient. The removal efficiency of TCr in a high potential group exceeds that in a low potential group by more than 10% under identical mineral filling conditions. Moreover, within the same potential gradient, the mineral filling position exerts a minimal influence on the remediation outcome. The stability analysis of Cr-containing products demonstrates a reduction in the Cr(VI) re-dissolution ratio by over 54% in the mineral-enhanced electro-remediation group, compared to the electrokinetic remediation group, indicating that the generated Cr-containing products are relatively stable and resistant to re-dissolution. Based on the analysis by Raman spectroscopy, XRD, and ESEM, Cr in stable mineral phases is correlated to Fe distribution.

Mineral-enhanced electro-remediation was the most effective approach for Cr(VI) removal. After 7 d operation of the device filled with minerals on both the sides and with a potential gradient of 0.4 V/cm, the overall removal efficiency of Cr(VI) and TCr was 100.0% and 95.7%, respectively. A potential gradient is the main factor affecting Cr(VI) treatment. The overall efficiency of total Cr was increased by more than 10% when the potential gradient was increased from 0.2 V/cm to 0.4 V/cm. The results of stability experiment showed that the amount of Cr(VI) re-dissolved from the electrodes, and the simulated soil in the mineral-enhanced remediation was close to zero, indicating that the remediation method had a long-term effect on the Cr(VI) treatment. The replacement of Fe³⁺ and SO₄^2- by Cr(III) and Cr(VI) in minerals was the main reason for maintaining the long-term effect of Cr(VI) treatment. This study could demonstrate the enhanced effect of magnetite/pyrrhotite composite mineral on the Cr(VI) removal, providing an effective approach for the long-term and stable remediation of Cr(VI)-contaminated sites.

Montmorillonite (MMT) nanosheets with large sizes is significant for controllable preparation of MMT functional nanocomposite materials. Compared with MMT, two-dimensional MMT nanosheets have a larger specific surface area, higher aspect ratio and richer hydroxyl groups at the edges. Therefore, MMT nanosheets are widely applied in the fields like environmental remediation, energy storage, flame retardant and membrane materials. The methods for preparing two-dimensional MMT nanosheets include mechanical milling, shearing, intercalation and ultrasonic exfoliation. However, the size of MMT nanosheets can be seriously damaged because of the higher external energy input of these exfoliation methods, thus affecting the applications. It is thus necessary to propose a new method for preparing MMT nanosheets with large sizes. In this paper, a method of MMT exfoliation was investigated based on its nature of osmotic hydration through weakening the interlayer binding energy of MMT. The exfoliation mechanism of MMT based on osmotic hydration was revealed via the conductivity analysis and molecular simulation. In addition, the regulation mechanism of exfoliation was also explored through the regulation of the water consumption and the concentration of MMT suspension during the osmotic hydration.

Sodium-exchanged MMT suspensions were stirred and dispersed. One end of a dialysis bag (a molecular weight cutoff of 3 000 Da) was sealed using a clamp. Subsequently, 100 mL of the suspensions was transferred into the dialysis bag, followed by sealing the other end with another clamp. Afterwards, the dialysis bag was placed in a beaker containing 500 mL of deionized water. The suspensions in the beaker was stirred in a magnetic stirrer at 200 r/min. Within the initial 12 h, the water in the beaker was refreshed every 3 h by pouring it out and replacing it with fresh deionized water. At 24 h and 36 h, the deionized water was replaced once again. At different time intervals, 2 mL samples were extracted from the dialysis bag using a pipette for subsequent test and analysis. These samples were labeled as MMT-t (where "t" represents the osmotic hydration time). The thickness of different two-dimensional MMT nanosheets was characterized by a model Multi Mode 8 atomic force microscope and a model JEM-F200 transmission electron microscope. Besides, the morphology of the two-dimensional MMT was determined by a model JSM 7100F scanning electron microscope.

MMT can be exfoliated into two-dimensional nanosheets during the osmotic hydration. The exfoliation degree of montmorillonite gradually increases with extending the osmotic hydration time to 48 h, which can achieve the thickness of MMT nanosheets similar to that of ultrasonic exfoliation. From the particle size distribution of MMT with dialysis time, the size distribution of MMT-48 is 48% in 0-300 nm and 30% in 300-600 nm, respectively. However, the size of MMT nanosheets using the same raw MMT material prepared by the ultrasonic exfoliation was distributed in the range of 100-300 nm. Therefore, the sizes of two-dimensional MMT nanosheets prepared by the osmotic hydration have more than twice greater than those by the ultrasonic exfoliation, demonstrating the effective preparation of two-dimensional MMT nanosheets with large sizes.

Furthermore, the exfoliation behavior of MMT through the osmotic hydration was investigated. The XRD patterns show that the a plane (001) of MMT appears a broad dispersion when the osmotic hydration time extends to 24 h, indicating that the laminar structure of MMT is destroyed and the exfoliation degree of MMT is increased. As the osmotic hydration time is 36 h or 48 h, the diffraction peaks corresponding to the crystal plane (001) of MMT disappear, exhibiting the emergence of an amorphous diffraction peak. This demonstrated that MMT is effectively exfoliated into nanosheets with a single layer or a few layers. The XRD patterns confirm that the exfoliation of MMT based on the osmotic hydration is achieved via promoting the hydration expansion. In addition, the exfoliation process is relatively slow and gentle, greatly protecting the size of MMT. There is osmotic pressure between MMT and the deionized water because of the concentration gradient between the interlayer cations of MMT and the deionized water in the surrounding environment. In osmotic pressure, more water molecules can penetrate into the interlayer of MMT, thereby promoting a further hydration exfoliation of MMT. The size of montmorillonite cannot be seriously damaged due to the increased hydration expansion force and low external input energy, resulting in the easier preparation of MMT nanosheets with large-sizes.

The thickness of MMT gradually decreased, but the size of MMT was barely damaged during the osmotic hydration, resulting in the effective preparation of two-dimensional MMT nanosheets with large sizes. The conductivity analysis and molecular simulation indicated that the exfoliation of MMT was controlled by the osmotic pressure between the interlayer cations and the external water. The exfoliation degree of MMT could be controllable with the water consumption and suspension concentration. The two-dimensional MMT nanosheets prepared by osmotic hydration had a thickness similar to that by ultrasonic exfoliation, and the size of MMT nanosheets prepared by osmotic hydration was twice greater than that by ultrasonic exfoliation.

The extraction and utilization of coal inevitably lead to the generation of significant solid waste, including coal gangue. This byproduct is rich in kaolin mineral resources, and their effective utilization presents a critical strategy for the management of such a bulk solid waste, offering substantial environmental and economic benefits. The processing methodologies are often hindered by the inherent mineralogical properties of the materials. Kaolinite minerals are central to the chemical reactivity in calcined coal kaolin clay, the content and characteristics of kaolinite can vary significantly in different coal kaolin sources due to the diversity in coal-forming geological conditions. It is thus necessary to clarify the mineralogical properties of kaolinite from various sources for the innovative application of coal gangue. In this paper, a high-iron coal-series kaolin clay was analyzed. In addition, the impact of mineralogical properties on the thermal activation and preparation of calcined kaolin clay was also investigated.

A high-iron coal-series kaolin clay was obtained as a representative sample from Sichuan, China. The chemical composition, phase composition, microstructure, and thermal behavior of the high-iron coal-series kaolinproperties were determined by X-ray fluorescence spectrometry (XRF), X-ray powder crystal diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetry-differential scanning calorimetry (TG-DSC).

The results reveal that the chemical composition of Yibin coal-series kaolin clay is predominantly composed of SiO₂, Al₂O₃ and Fe₂O₃, with small contents of CaO, MgO, SO₃ and TiO₂, accounting for a total oxide mass of 71.84%. This coal-series kaolin clay could be categorized as high-iron coal-series kaolin clay because the content of Fe₂O₃ is 8.54%. The coal-series kaolin clay calciated exhibits a loss mass of 28.14%, which is attributed to the volatile matter and fixed carbon (15% in the mass). The principal minerals of high-iron coal-series kaolin clay along with their respective mass fractions are low-crystallinity kaolinite (56%), quartz (12%), and iron-bearing minerals such as goethite (Gth, 3%), hematite (Hem, 3%), siderite (Sd, 3%), and pyrite (Py, 2%). Furthermore, a small amounts of calcite (Cal, 3%) and anatase (Ant, 1%) also appear. The micro-morphology of the kaolinite is thin flakes or tightly stacked layers of minerals with a diameter of less than 5 μm, having a distinct laminar dissolution, and edges encrusted with small particles of calcite, quartz, anatase and other minerals.

In the calcination process, kaolinite initiates the loss of hydroxyl groups at 413 ℃, and the crystalline layers progressively become disordered at 550 ℃. It completely transforms into amorphous metakaolin at 830 ℃, accompanied by a total weight loss of 26.24%. Hematite is ultimately formed through the oxidation of pyrite and siderite, releasing volatile components such as SO₂ and CO₂. Goethite also converts to hematite, leading to an increased hematite content in the calcined product, which remains more stable at <900 ℃. In the thermal activation experiment, the kaolinite in coal gangue kaolin clay undergoes a maximal transformation into amorphous metakaolin, entailing the removal of a substantial number of hydroxyl groups and the disruption of the alumina octahedral sheet structure. This results in a shift of aluminum coordination to five-fold (Al^V), creating amorphous Al₂O₃, SiO₂, and numerous broken bonds, significantly enhancing chemical reactivity. At 750 ℃, the dissolution rate of Al₂O₃ peaks is 68.47% by mass. These results imply that the structural evolution of kaolinite at elevated temperatures is closely related to the activation process of kaolinite in Yibin coal gangue kaolin clay.

The results showed that heat treatment could transform Yibin coal gangue kaolin clay into calcined kaolin clay as a resource. This synthetic pozzolanic material exhibited favorable hydration properties, rendering it suitable for the fabrication of high-performance building materials, such as thermally insulated walls, thereby contributing to the conservation of resources and energy. This material could also have a potential for the partial substitution of cement in cementitious systems like concrete and geopolymers. This study could provide a mineralogical foundation and offer a developmental guidance for the comprehensive utilization of high-iron coal-series kaolin clay.

Mycotoxins are secondary metabolites with a high toxicity produced by fungi and widely exist in feeding, thus reducing feed quality and affecting human-being and animal health. Montmorillonite as a feed additive can effectively reduce the risk of mycotoxin absorption by organisms, but its surface is highly hydrophilic, and the binding rate with weak/non-polar mycotoxins (such as OTA) is low. In this paper, OTA/montmorillonite composite adsorption material (i.e., CPC-MT) was prepared with pyridine salt CPC as a modifier. Its structure before and after montmorillonite modification was analyzed. The OTA adsorption behavior of modified montmorillonite was investigated through batch adsorption experiments combined with kinetic and isothermal adsorption models, so as to provide a technical scheme for effective adsorption of mycotoxins in feed.

Cetylpyridine chloride (CPC) modified montmorillonite was prepared in water bath under stirring. The modified product was obtained by centrifugal washing, drying, grinding and sieving. The layer spacing, functional groups and hydrophilicity (i.e., contact angle) of montmorillonite before and after modification were determined by X-ray diffraction (XRD), Fourior tranform infrared spectroscopy (FTIR) and contact angle measurement. In a simulated body fluid environment at different pH values, the adsorption effect of montmorillonite on OTA before and after modification was analyzed, and the adsorption mechanism was further discussed through adsorption kinetics and adsorption isotherm.

The XRD analysis shows that the crystal surface spacing of montmorillonite after CPC modification gradually increases from 1.25 nm to 1.52 nm with the increase of the amount of modifie. The layer spacing of montmorillonite at 1.5 CEC is the maximum, and gradually shifts to a lower angle as the amount of modifier increases. These results indicate that the long carbon chains entering the interlayer or CPC of CP⁺ after ion exchange with the interlayer cations of montmorillonite are combined with montmorillonite due to the electrostatic interaction. According to the organic cation chain length, the angle between the layers of montmorillonite and the layer spacing, the CPC is arranged in the interlayer of montmorillonite at an angle of 13.6°. From the FT-IR analysis, the antisymmetric and symmetric tensile vibration and shear vibration of -CH₂ in CPC and the C-H stretching vibration on CPC benzene ring appear in organic modified montmorillonite, and the intensity of the -CH₂/C-H absorption peak of CPC gradually increases, resulting in a certain degree of change in the lattice of montmorillonite. This indicates that CPC and montmorillonite are combined. From the contact angle analysis, the surface of montmorillonite changes from hydrophilic to hydrophobic, and CP⁺ between montmorillonite layers basically reaches a saturation value at 1.5CEC. The TGA analysis shows that CPC-Mt has a mass loss peak with increased decomposition of organic matter, decreased surface adsorbed water, and increased organic carbon content, which is conducive to the OTA adsorption.

The results of batch adsorption experiment show that as the amount of modifier increases the adsorption rate of X-NMt to OTA is 36.0%, and the adsorption rate of 0.5-2.0 CPC-Mt to OTA is 51.3%, 70.0%, 77.1% and 77.5%, respectively. In addition, the adsorption effect of CPC-Mt on OTA at a certain pH value of a simulated intestinal fluid is slightly better than that of gastric fluid, indicating that no OTA desorption occurs during the whole process of a simulated body fluid.

CPC entered the interlayer of montmorillonite, and the montmorillonite changed from hydrophilic to hydrophobic when using CPC modified montmorillonite. When CPC-Mt was used to adsorb OTA in simulated animal body fluids, the adsorption rate of CPC-Mt increased from 36.0% to 77.5%, compared with that of X-NMt. The adsorption behavior of OTA by CPC-Mt followed the quasi-second-order kinetic adsorption model, indicating that OTA adsorption was controlled by chemical reaction. The adsorption process followed the adsorption/distribution model, and the transformation of CPC-Mt from hydrophilic to hydrophobic played a key role in the adsorption of weak polar OTA. According to the adsorption mechanism analysis, the organic carbon chain of CP⁺ was used as a distribution medium, and the organic part of OTA was absorbed into the modified montmorillonite through hydrophobic distribution when CP⁺ was inserted into montmorillonite. OTA and CP⁺ could adsorb each other due to the electrostatic interaction.

Red mud is a solid waste generated from alumina production, its massive accumulation occupying extensive land areas and leaching alkalis and heavy metals, leading to significant environmental issues such as soil alkalization and groundwater pollution. This study responds to the current demand for sponge city construction via innovatively utilizing red mud as a raw material to produce un-sintered aggregates through a novel pelletization process that leverages similarities between red mud and permeable brick materials. High-strength un-sintered permeable bricks were prepared via integrating mixing, molding, and curing techniques. These bricks improve overall compressive strength and permeability, while drastically reducing energy consumption and environmental impact during production. This approach presents a fresh perspective on red mud utilization and sponge city development, promising the environmental and economic benefits.

The preparation of red mud-based unsintered permeable bricks involved: 1) pelletization, the aged red mud chunks were crushed, then mixed uniformly with P·O 42.5 ordinary Portland cement and water, and fed into a pelletizer for pelletization. The aggregated particles were removed and naturally cured for one week; 2) mixing, different proportions were designed based on a volumetric method, with red mud-based un-sintered aggregates, cement, water, and additives calculated and weighed according to these proportions, then added to a basin and mixed uniformly; 3) pressing, the uniformly mixed slurry was placed and pressed into a mold with the dimensions of 20 cm×15 cm×10 cm by a semi-automatic brick machine; 4) curing, the pressed permeable bricks were demolded and naturally cured for 1-2 d, then placed in a standard curing box for 28 d.

The phase structure and micro-morphology of the material were analyzed by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The heavy metal leaching performance of the permeable bricks was analyzed according to the national standards (HJ557-2010). The concentrations of ten metal elements in the leachate were determined inductively coupled plasma mass spectrometry (ICP-MS). In addition, the environmental risk of heavy metal elements in the leachate was evaluated according to the national standards (GB/T 5085.3-2007).

The bulk density (ρ_bv) of red mud-based aggregates is 1 078.50 kg/m³, with an apparent density (ρ_ap) of 1 724.14 kg/m³ and a porosity (v) of 37.45%. The analysis of the water-cement ratio (w_c) on permeable brick performance reveals that increasing w_c from 0.20 to 0.35 gradually enhances the compressive strength. This improvement stems from the increased fluidity and adhesive properties of the cement paste at a higher w_c, facilitating a better aggregate encapsulation and thereby improving the connectivity. However, increasing w_c beyond 0.35 to 0.40 results in a significant decrease in the compressive strength likely due to excessive fluidity causing settling of the cement paste.

The results of target porosity effect on permeable bricks demonstrate a negative correlation with the compressive strength and a positive correlation with the permeability coefficient. A greater porosity leads to increased interconnected pores within the bricks, enhancing water infiltration but reducing contact points crucial for stress transmission. This leads to localized increases in pressure and higher susceptibility to fracturing, thereby impacting the mechanical properties.

The results of foaming agent content effect on permeable brick performance indicate that increasing the foaming agent from 0% (in mass fraction) to 4% slightly increases the permeability coefficient, while marginally decreasing compressive strength. This effect results from hydrogen peroxide decomposition, creating additional pores within the bricks that weaken aggregate bonding and increase porosity. A further increase in foaming agent content reduces the permeability coefficient, while gradually enhancing compressive strength.

The XRD analysis confirms CaCO₃ as a common component in red mud, cement, aggregates, and permeable bricks. The characteristic peaks of red mud and aggregates remain unchanged, indicating no alteration in primary phases of red mud under the un-sintered process. In the permeable bricks, the characteristic peaks of 3CaO·SiO₂ are absent, whereas the peaks of Ca₅(Si₆O₁₆)(OH)₂ appear. This indicates that 3CaO·SiO₂ undergoes a reaction with water under high alkalinity conditions to produce Ca₅(Si₆O₁₆)(OH)₂, consequently boosting the bricks' strength. The microstructural observation of cross-sections and vertical sections reveals abundant micro-voids crucial for permeability. The cross-sections display flaky hydration gels distributed along aggregate surfaces, while the vertical sections exhibit thinner hydration products and flocculent gels.

The results of heavy metal leaching experiments reveal chromium (Cr) as the maximum concentration metal in leachates from red mud-based un-sintered permeable bricks, exceeding 40 μg/L, while other metals are below 10 μg/L. Leachate toxicity is well below the values of the national standards (GB/T 5085.3-2007), confirming compliance with environmental safety standards and minimal environmental risk for red mud-based un-sintered permeable bricks.

Red mud-based un-sintered permeable bricks were prepared through pelletization, mixing, pressing, and curing. The water-cement ratio affected brick's performance. An increase in the water-cement ratio enhanced the fluidity of the slurry and increased compressive strength, but when the ratio exceeded 0.35, the mechanical properties deteriorated. Increasing the target porosity improved permeability but reduced compressive strength. Adding hydrogen peroxide as a foaming agent effectively increased porosity at levels below 4%, but excessive addition led to the reduced performance. The XRD analysis showed that a high alkalinity of red mud promoted the formation of C-S-H gel, enhancing compressive strength. The SEM images of the cross and vertical sections of the permeable brick revealed flaky and flocculent hydration gel products attached to the surfaces of the aggregates. The results of heavy metal leaching experiments indicated that the leaching risk of heavy metals from the permeable bricks was extremely low. This work could provide an effective approach to simultaneously address the challenges of red mud resource utilization and sponge city construction.

Zearalenone (ZEN) as an estrogenic fungal toxin produced by Fusarium graminearum widely presents in grains, corn, wheat and their by-products. The presence of ZEN seriously endangers the health of animal and humanbeing due to the reproductive toxicity, immunotoxicity, genotoxicity, carcinogenic and teratogenic effects. The adsorption method is the most effective way to remove ZEN, and the commonly used adsorbents are silicate minerals. Attapulgite is an advantageous resource in China, which is used as a feed material to enhance immune function and antioxidant capacity, promote intestinal health, and improve animal production performance and product quality. However, it is difficult to realize the efficient removal of low polarity and hydrophobic ZEN using hydrophilic and negatively charged attapulgite. It is thus indispensable to modify attapulgite with cationic surfactants to enhance their surface hydrophobicity and adsorption property toward ZEN. Imidazole ionic liquid surfactant C_nmimBr has lower critical micelle concentration, higher adsorption efficiency and better surface properties than conventional surfactants with the same carbon chain length. In this paper, attapulgite was modified with ionic liquid surfactant C_nmimBr for the efficient adsorption of ZEN.

APT (25.0 g) was dispersed in 250 mL distilled water at a stirring rate of 540 r/min to form a uniform suspension, and different types of C_nmimBr (i.e., C₁₂mimBr, C₁₄mimBr, C₁₆mimBr, and C₁₈mimBr) were added into the suspension with different concentrations (i.e., 0.5%, 1.0%, 2.5%, 3.0%, and 5.0%), respectively. The mixtures of C_nmimBr and APT were stirred at room temperature for 4 h, and then the solid products labeled as C_nmimBr-APT nanocomposites were centrifuged, washed with deionized water until no bromine ions, dried at 105 ℃ for 4 h, and ground to the fine particles below 75 µm.

The removal ratio of C_nmimBr-APT nanocomposites toward ZEN was determined via batch experiments. The influences of C_nmimBr amounts and carbon chain length on the adsorption performance for ZEN were investigated. 1.0% C₁₆mmBr-APT, 2.5% C₁₆mmBr-APT, and 5.0% C₁₆mmBr-APT were selected as adsorbents to investigate the effect of adsorption condition (i.e., adsorbent dosage, contact time, pH value, initial concentration, and coexisting nutrients) on the adsorption performance of ZEN. The adsorption process was analyzed using kinetic and thermodynamic models.

According to the Fourier transform infrared spectra, the relative intensity of C―H bonds at 2 930 cm^-1 and 2 865 cm^-1, and C=N at 1 630 cm^-1 gradually increases with the increase in the carbon chain length and added amount of C_nmimBr, indicating that C_nmimBr is anchored on the APT surface to realize the organic modification. Meanwhile, the organicization degree also increases with the increase in the carbon chain length and C_nmimBr dosage. Furthermore, the modification process does not change the crystal structure of APT, but the specific surface area reduces with the increase in the hydrophobicity, which is beneficial to the efficient removal of ZEN through hydrophobic interaction.

The in-vitro adsorption experiments indicate that the adsorption performance of C_nmimBr-APT nanocomposites is positively associated with C_nmimBr dosage and carbon chain length. The adsorption process follows the pseudo second order kinetic model and Langmuir isotherm. When the modified amount of C₁₆mimBr is 5.0%, the maximum adsorption capacity of C₁₆minBr-APT nanocomposites to ZEN is 7.45 mg·g^-1. Furthermore, pH value and co-existed nutrients (e.g., amino acids, vitamins and minerals) have little effect on the adsorption performance of ZEN.

The novel ZEN adsorbents were prepared based on the organic modification of APT using C_nmimBr with different carbon chain lengths. The results indicated that C_nmimBr modification did not change the crystal structure of APT, while the surface hydrophobicity increased with the increase in the carbon chain length of C_nmimBr. Meanwhile, the adsorption capacity of C_nmimBr-APT nanocomposites toward ZEN increased with the increase in the C_nmimBr dosage, carbon chain length, adsorbent dosage, and initial solution concentration. The adsorption mechanism was mainly due to the hydrophobic interaction between the long organic carbon chains of C_nmimBr and ZEN molecules, and C_nmimBr-APT nanocomposites presented a considerable application potential for the removal of ZEN adsorbents due to the good selective adsorption in the presence multiple nutrients.

Sulfate radical-based advanced oxidation processes (SR-AOPs) are a highly promising technology for water treatment, and their processing capacity is affected by the catalyst. However, the existing catalysts are mostly powder-based and cannot meet the requirements of recovery and mass transfer in practical applications. Catalytic filtration membrane is a functional membrane that combines catalysis and filtration. It provides a support for the catalyst to ensure its recovery, and restricts the reaction to pores, facilitating a close contact between pollutants and active sites, thereby achieving efficient utilization of peroxymonosulfate. Sepiolite is an excellent catalyst carrier because of its excellent thermal stability, great adsorption capacity, and abundant acid-base sites. In addition, sepiolite is a high-quality film-making material with fibers interwoven into a mesh structure in the same or different directions. In the paper, we prepared a CuO/sepiolite catalytic filtration membrane (CuO/sepiolite) with excellent catalytic performance via impregnation-filtering coating-drying-calcination. In addition, the performance and activation mechanism of catalyzing peroxymonosulfate method were also investigated.

0.1g sepiolite was dispersed in 20 mL of 20 mmol/L Cu(NO₃)₂ solution to obtain a suspension A. The suspension A was heated at 30 ℃ and stirred continuously for 3 h. The mixed suspension was filtrated through polyethylene (PE) microfiltration membrane (0.45 μm) and dried at 60 ℃ for 12 h to obtain a precursor. The dried precursor was placed in a muffle furnace and heated at 400 ℃ for 2 h to obtain a catalytic membrane. The catalytic membrane was cut into a circle with a diameter of 50 mm (named CS). A series of catalytic membranes were prepared at different calcination temperatures (i.e., 300, 400, 500, 600 ℃ and 700 ℃) (named CS-X, where X represents the calcination temperature).

The chemical composition of the samples was determined by X-ray fluorescence spectroscopy (XRF). The Cu content was quantitatively measured by an acid dissolution method combined with inductively coupled plasma atomic emission spectroscopy (ICP-AES). The crystal structure was analyzed by X-ray powder diffraction (XRD). The functional groups on the surface of catalytic filtration membranes were detected by Fourier transform infrared spectroscopy (FTIR). The microstructure and structural characteristics of the membrane material were determined by scanning electron microscopy (SEM) and high-resolution transmission electron microscopy.

A lab-scale catalytic filtration system was established to evaluate the catalytic performance of the CS. The inside diameter of filtration is 50 mm and the valid test area of CS is 19.6 cm². The simulated wastewater flowed through the catalytic filtration from top to bottom at a certain flow rate. Before catalytic degradation, a feed PNP solution firstly flowed through the catalytic filtration system to achieve adsorption-desorption equilibrium, and then the catalytic reaction was started by adding a specific mass of peroxymonosulfate (PMS). After a specific interval, filtrate was collected for measurement of absorbance, ion leaching concentration and TOC in alkaline conditions. The removal ratio (R) is calculated by

The catalytic filtration membrane (CS-400) has the optimum catalytic performance when the calcination temperature is 400 ℃ and the concentration of copper nitrate solution is 20 mmol/L. After the continuous catalytic degradation of 15 L of p-nitrophenol solution at a concentration of 10 mg/L, the performance of CS-400 catalytic filtration membrane does not show any degradation, and its structure is not damaged. Hydroxyl radical is the main reactive oxygen species for the degradation of p-nitrophenol in this catalytic reaction system. The CuO/sepiolite catalytic filtration membrane is a potentially valuable peroxymonosulfate catalyst with the promising applications in wastewater treatment.

A novel CuO/sepiolite catalytic filtration membrane was prepared according to the process route of impregnation-filtering-forming-drying-calcination for activating peroxymonosulfate. When the calcination temperature was 400 ℃ and the concentration of Cu(NO₃)₂ was 20 mmol/L, the prepared catalytic filter membrane (CS-400) had the best catalytic performance. After the continuous catalytic degradation of 15 L of p-nitrophenol solution at a concentration of 10 mg/L, the performance of the CS-400 catalytic filtration membrane did not show significant degradation, and its structure was not significantly corroded. The hydroxyl radical is the main reactive oxygen species for the degradation of p-nitrophenol in this catalytic reaction system, and the CuO/sepiolite catalytic filtration membrane is a potentially valuable peroxymonosulfate catalyst for the application in wastewater treatment.

Tourmaline is a kind of borosilicate mineral with complex structure and composition, which is used in the fields of functional materials, environmental protection and healthcare. Since the positive and negative charge centers of tourmaline do not coincide, tourmaline has a natural spontaneous polarization that is one of the most important properties, having its application in various fields. In previous studies, the changes of element occupancy, valence proportion of key elements and crystal structure parameters in tourmaline cause the lattice distortion, resulting in a change of spontaneous polarization intensity. It is thus of great significance to reveal the relationship among the composition, structure and property of tourmaline. In this paper, the control path along iron speciation-microstructure-spontaneous polarization of Fe-Mg tourmaline was investigated to clarify the structure-activity relationship dominated by cation occupancy in Y-site of tourmaline and propose the optimal configuration of tourmaline with the excellent performance.

Six single crystals of tourmaline samples with different Fe contents were collected from different locations in China (i.e., Hebei province, Xinjiang province, Yunnan province and Guangxi province), respectively. After digestion, the chemical compositions of the samples were determined by ICP. The natural tourmaline was crushed by a model RH-800 high-speed multifunctional pulverizer (Zhejiang Ronghao Industry and Trade, China), and ground by a model XPM-Φ100×4 planetary muller (Wuhan Prospecting Machinery Factory, China). The composition of tourmaline was determined by a model 7700x inductively coupled plasma optical emission spectrometry (ICP-OES, Agilent Co., USA). The crystallographic structure of tourmaline was examined by a model X'Pert PRO X-ray diffractometer (XRD, PANalytical B.V., the Netherlands) with Cu K_α radiation over a 2θ range between 3° and 80°. The occupancy of Fe²⁺ and Fe³⁺ at Y and Z sites of tourmaline was characterized by a model MVT-1000Mossbauer spectrometer (Wissel Co., Germany). The crystal structure of tourmaline was characterized by a model Smart APEX-CCD X-ray single-crystal diffractometer (Bruker Co., Germany) with Mo Kα radiation, and the structure refinement was completed by a crystallography software named SHELXS-97. The spontaneous polarization intensity was measured quantitatively and indirectly by an alkali solution method.

The structure difference due to different composition of tourmaline is mainly caused by the element change in Y site, in which Fe element plays a crucial role. Based on the calculation of intrinsic electric dipole moment, the spontaneous polarization intensity of tourmaline along the c-axis is more intense than that in other directions (cylinder), and the T polyhedron is the largest contributor to the intrinsic electric dipole moment of tourmaline. The intrinsic electric dipole moments generated by each polyhedron along the a and b axes cancel each other due to the toroidal symmetrical structure of tourmaline, resulting in a small total intrinsic electric dipole moment.

The intrinsic electric dipole moment and the spontaneous polarization intensity of the six tourmaline samples are in the order GX-1>YN-1>XJ-1>HB-1>XJ-2>HB-2. The more intense the polyhedral distortion is, and the larger the intrinsic electric dipole moment and the more intense the spontaneous polarization will be. For tourmalines with Fe content that is higher than Mg content, the polyhedron distortion of tourmaline and the intrinsic electric dipole moment increase with the increase of Fe²⁺ content and iron atom in Z site. For tourmalines with Fe content that is lower than Mg content, the structure distortion and the intrinsic electric dipole moment decrease with the increase of Fe content, and increases with the increase of Fe²⁺ content.

For the Fe-Mg tourmalines, the Y site is mainly occupied by Fe atoms and Mg atoms, and the change of Mg/Fe molar ratio directly affects the expansion and deformation of Y polyhedron, resulting in the change of tourmaline structure. After the intrinsic electric dipole moment of tourmaline is analyzed at different Mg/Fe ratios, the intrinsic electric dipole moment of tourmaline decreases with the decrease of Fe content when the molar ratio of Mg/Fe is less than 1. This is due to the decrease of Fe²⁺ content, leading to the weakening of structural distortion. The intrinsic electric dipole moment of tourmaline increases with the decrease of Fe content when the Mg/Fe molar ratio is greater than 1, which is consistent with the previous results. For tourmaline with Fe content that is lower than Mg content, the lower the Fe content is, and the more intense the structural distortion and the greater the inherent electric dipole moment will be. When the Mg/Fe molar ratio is greater than 2, the intrinsic electric dipole moment and the spontaneous polarization intensity of tourmaline at different Mg/Fe molar ratios become stable.

For tourmalines with Fe content that was higher than Mg content, the cell volume increased with the increase of magnesium content, and the polyhedron distortion of tourmaline and the intrinsic electric dipole moment increased with the increase of Fe²⁺ content and iron atom in Z site. For tourmalines with Fe content that was lower than Mg content, the cell volume increased with the increase of Fe content, the structural distortion and the intrinsic electric dipole moment decreased with the increase of Fe content, and increased with the increase of Fe²⁺ content. The results of spontaneous polarization test showed that the characteristic properties of tourmaline were consistent with the intrinsic electric dipole moment. The configuration structure-function relationship of tourmaline with Fe as a main factor was revealed via analyzing the variation trend of intrinsic electric dipole moment under the dominance of Y-end positive ion. The performance of tourmaline decreased with the decrease of Fe content when the Mg/Fe molar ratio was less than 1. The performance of tourmaline increased with the decrease of Fe content when the Mg/Fe molar ratio was greater than 1. The spontaneous polarization increased when the Mg/Fe molar ratio was greater than 2.

Hydrophobic organic pollutants in industrial wastewater and oil spillage have attracted wide attention. It is thus important to develop a variety of adsorbents like activated carbon, biochar, zeolite, graphene, etc.. However, carbon-based porous materials exhibit poor thermal stability and flammability, having secure risks during high-temperature applications and thermal regeneration processes. Silicon-based porous materials like zeolite are complex to prepare and difficult to effectively remove multiple organic pollutants simultaneously. Montmorillonite-based adsorbents become popular due to their low cost and environmental friendliness. However, montmorillonite as a powder has challenges in practical applications such as clogging, leakage, and recovery difficulties. It is thus effective in converting montmorillonite into fixed-form aerogel materials.

Polyurethane sponge (PU) as an ideal substrate for developing porous aerogels can enhance the mechanical properties of the adsorbents due to its biodegradability, affordability, low density, and customizable dimensions. In this paper, low-density, recyclable, and cost-effective organic montmorillonite/polyurethane sponge composite aerogels were prepared via ultrasonic swelling and freeze-drying. The composite aerogel was evaluated for its adsorption/absorption capabilities towards benzene, bisphenol A, nitrobenzene, oils, and organic solvents. In addition, the reusability and flammability characteristics of the aerogel were also analyzed.

An organic montmorillonite (i.e., C16Mnt) was prepared with cetyltrimethylammonium bromide to modify montmorillonite. 1 g C16Mnt was added to 20 mL organic solvent (the mass ratio of cyclohexane to tertiary butanol is 9∶1) to prepare a suspension C16Mnt. Chitosan sol was then introduced into the suspension C16Mnt and agitated in a water bath at 50 ℃ for 3 h, yielding a homogeneous sol. Subsequently, PU was immersed in the sol for 5 min to ensure a complete absorption. The sol-loaded PU was subsequently aged at 25 ℃ for 12 h, facilitating the transformation of the sol into a gel. The organic montmorillonite/polyurethane sponge composite aerogel (i.e., PU/CS-C16Mnt) was fabricated via freezing the gel in liquid nitrogen for 10 min and subsequently freeze-drying for 48 h. The composite aerogels, differing in densities (PU25 and PU35), were denoted as PU25/CS-C16Mnt and PU35/CS-C16Mnt, respectively.

PU has a three-dimensional porous network structure and a smooth surface on its skeleton. The pore structure of PU undergoes a significant change after loading with CS-C16Mnt. The pores are filled with numerous organic montmorillonite clusters, resulting in a rougher surface, which is favorable for enhancing the adsorption performance. The incorporation of CS-C16Mnt also improves the hydrophobicity of PU. Furthermore, the infrared spectroscopic analysis reveals that CS-C16Mnt is loaded onto the PU skeleton through covalent bonds and hydrogen bonds formed between PU and CS-C16Mnt.

The PU/CS-C16Mnt exhibits exceptional adsorption capabilities for organic pollutants, based primarily on organic distribution and pore-filling mechanisms. The adsorption results indicate that PU25/CS-C16Mnt has the maximum static adsorption performance for benzene (i.e., 682.3 mg/g). This superior performance can be attributed to the intense interactions with the benzene molecules and C16Mnt, as well as the presence of an abundance of macropores. Besides, PU25/CS-C16Mnt has excellent adsorption properties for bisphenol A and nitrobenzene, achieving adsorption capacities of 339.8 mg/g and 137.0 mg/g, respectively. The infrared spectroscopic results show that O―H and N―H in PU25/CS-C16Mnt participate in the adsorption process. The cyclic adsorption results show that the adsorption capacity of PU25/CS-C16Mnt for bisphenol A decreases from 208.4 mg/g to 154.7 mg/g, and the adsorption capacity of nitrobenzene decreases from 57.9 mg/g to 41.6 mg/g, which is still higher than that of original PU25.

Furthermore, PU25/CS-C16Mnt has good hydrophobicity and lipophilicity, which can selectively absorb oil and organic solvents with the maximum absorption capacity (i.e., 20.8~37.0 g/g) of xylene, gasoline, liquid paraffin, dimethyl silicone oil and carbon tetrachloride. After 10 repeated experiments, the absorption capacity can still maintain 82.8% of the first absorption capacity. Also, PU25/CS-C16Mnt has a good absorption performance (i.e., 7.12 g/g) for grease in actual sewage, and it is easily recyclable. The combustion behavior of PU25/CS-C16Mnt reveals that the incorporation of organic montmorillonite significantly enhances the flammable retardancy of pure PU.

Organic montmorillonite/polyurethane sponge composite aerogel with low-density (i.e., 34.61 mg/cm³), highly hydrophobic and low flammability was synthesized via ultrasonic swelling and freeze-drying. The montmorillonite/polyurethane sponge composite aerogel exhibited exceptional adsorption capabilities for organic pollutants, relying primarily on organic distribution and pore-filling mechanisms. The aerogel demonstrated a static adsorption capacity of 682.3 mg/g for benzene vapor and respective adsorption capacities of 339.8 mg/g for bisphenol A and 137.0 mg/g for nitrobenzene. The absorption capacity for various oils and organic solvents ranged from 20.8-37.0 g/g, with the excellent reusability. Furthermore, montmorillonite/polyurethane sponge composite aerogel exhibited a good adsorption/absorption performance (i.e., 7.12 g/g) for organic contaminants in actual wastewater. This aerogel could be used as a promising montmorillonite-based adsorption material for the treatment of organic pollution.

The utilization of HNT is undergoing a rapid expansion with forthcoming research prospects. In China, high-purity HNT deposits are notably scarce, with most deposits primarily consisting of mixed halloysite-kaolinite deposits. Consequently, there exists a pressing necessity for the advancement of efficient HNT beneficiation or purification methodologies to segregate HNT from kaolinite. Also, there is a growing emphasis on exploring the assembly of HNT into nanomaterials with diverse functional properties, alongside a concerted effort to unravel the influence of HNT surface characteristics, morphology, and structural attributes on the performance of composite materials. Furthermore, it is imperative to align research endeavors with national strategic imperatives, bolstering the development of HNT-based composite functional materials in harmony with the national non-metallic mineral development strategy, particularly within sectors such as information technology, biotechnology, and new energy applications.

The great interest in application of halloysite as an environmental mineral material is due to its unique physicochemical properties such as tubular structure, hydrophilicity, high specific surface area, high stability, ion exchange capacity and negatively charged external surface. The application performance of halloysite in environmental pollution control fields such as water treatment and air pollution control can be greatly improved through surface modification or nanoparticle loading. However, it is necessary to address the corresponding science and technique problems. For instance, it is difficult to achieve 100% pollutant removal efficacy by halloysite in actual complex and diverse natural environments. The recovery and regeneration of halloysite powder after use should be also considered. The large-scale purification technology and surface modification technology of halloysite need to be further optimized. The future development direction in this area includes understanding the interfacial interaction mechanism, optimizing the production process, expanding the application field, and strengthening the combination with other technologies to improve the treatment efficacy. Halloysite is a promising and cost-effective material in pollutant treatment, and future studies should pay more attentions to the improvement of operability, regeneration and processing capacity in practical applications.

Bi₂Te₃-based alloys are the most well-known thermoelectric materials for room-temperature applications. The existing Bi₂Te₃-based thermoelectric materials produced commercially are prepared by a zone melting method, resulting in highly oriented materials with high thermoelectric properties. However, the ingots produced by the zone melting method are prone to disintegration due to the weak van der Waals forces between the layers of Te atoms, leading to the poor mechanical properties and the proclivity for fracture during processing and practical applications. It is thus important to improve the mechanical properties and machinability of Bi₂Te₃-based materials with the excellent thermoelectric properties. This work was to prepare a n-type Bi₂Te_2.7Se_0.3 thermoelectric material via spark plasma sintering combined with hot extrusion (SPS+HE). The parameters affacting hot extrusion process and preparation of n-type Bi₂Te_2.7Se_0.3 materials under different process conditions were optimized, and the thermoelectric performance and mechanical properties were investigated. In addition, the machinability of the extruded Bi₂Te_2.7Se_0.3 material was also analyzed.

The commercial zone-melting crystal rods were pulverized and sintered via spark plasma sintering (SPS) at 350 ℃ and 20 MPa for 5 min. The ingot was then put into a hot extrusion mold, and treated at 390-550 ℃, extrusion speed of 0.05-0.50 mm/s, extrusion ratio of 9∶1, and extrusion angle of 30°. Under the determined hot extrusion parameters, n-type Bi₂Te_2.7Se_0.3 materials were prepared by different processes, i.e., the raw materials were ground for 1 h and then sintered by SPS and subsequent hot extrusion (HE); the raw materials were melted at 700 ℃ for 5 h and then cold-pressed (MT), and sintered by subsequent hot extrusion (HE); the raw materials were melted and cold-pressed, followed by annealing and hot extrusion (MT+AN+HE); and the raw materials were ground for 1.5 h and cold-pressed, followed by hot extrusion (BM+HE). The phase structure was analyzed by X-ray diffraction (XRD, D8 Advance, Bruker Co. Ltd., USA) at room temperature. The microstructure and fracture morphology were determined by scanning electron microscopy (SEM, Supra 55, ZEISS Co., Germany). The electrical conductivity and the Seebeck coefficient were measured by ZEM-3 (ULVAC Co. Ltd., Japan). The thermal diffusivity (λ) was measured by a laser flash method (LFA457, Netzsch Co., Germany). The thermal conductivity was calculated according to κ=λρC_p, where C_p was the heat capacity according to the Neumann-Kopp rule, and the density ρ was measured based on the Archimedes prinicple.

The results show that n-type Bi₂Te_2.7Se_0.3 thermoelectric materials can be prepared under optimum process conditions (i.e., extrusion temperature of 400 ℃ and extrusion speed of 0.05 mm/s). The XRD patterns of all the hot-extruded samples agree well with a rhombohedral structure (JCPDS 50-0954) of Bi₂Te_2.7Se_0.3. No impurity peaks appear. The SEM images reveal that Bi, Te, and Se are homogeneously distributed in the materials without any impurity phases. The electrical conductivity σ of all the samples decreases with increasing temperature, having a metallic conduction behavior. The σ of the MT+AN+HE sample is the maximum value of 1.4×10⁵ S/m. All the samples have negative Seebeck coefficients S, indicating that electrons are the major charge carriers. The S of the SPS+HE sample is the maximum value of 191.0 μV/K. At 300 K, the SPS+HE sample has the maximum power factor PF of 37.0 μW/(cm·K²). However, the PF of the material gradually decreases with the increase of temperature, which is consistent with the change of electrical conductivity and Seebeck coefficient due to the intrinsic excitation. The lattice thermal conductivity of MT+HE sample is the minimum value (i.e., 0.9 W·m^-1·K^-1). The maximum zT value reaches 0.83 at 400 K for SPS+HE sample and its Vickers hardness is 602.5 N/mm², which is twice greater than that of the zone-melting sample. This is mainly due to the dynamic recrystallization process of grain refinement during the hot extrusion process. The machinability of the extruded Bi₂Te_2.7Se_0.3 material are improved. The thermoelectric micron-sized particles with a minimum size of 147 μm can be achieved, providing a promising material for the development of Bi₂Te₃-based thermoelectric micro-devices.

The optimal hot extrusion process parameters for n-type Bi₂Te_2.7Se_0.3 thermoelectric materials were obtained (i.e., extrusion ratio 9∶1, extrusion angle 30°, extrusion temperature 400 K and extrusion speed 0.05 mm/s). A series of n-type Bi₂Te_2.7Se_0.3 thermoelectric material samples were prepared via hot extrusion under the optimum process conditions. The Bi₂Te_2.7Se_0.3 sample prepared by SPS and sebsequent hot extrusion (SPS+HE) had the maximum zT value 0.83 at 400 K, and its mechanical properties were improved. The Vickers hardness of the SPS+HE sample could reach 602.5 N/mm², which was twice greater than that of the zone-melting Bi₂Te_2.7Se_0.3 material. In addition, the machining performance was also improved, and the thermoelectric micron-sized particles with the minimum size of 147 μm could be machined for the extruded Bi₂Te_2.7Se_0.3 sample, providing a promising material for the Bi₂Te₃-based thermoelectric micro-devices.

Silicon is considered as one of the most promising lithium anode materials due to its high lithium storage capacity. However, the volume expansion effect and semiconductor properties of silicon hinder its practical application. Two effective strategies exist for mitigating this issue, i.e., reducing the size of silicon to nanoscale; and introducing non-active matrices to improve stability and conductivity. In recent decades, the incorporation of iron silicide (FeSi₂) with silicon (Si) has attracted much attention due to its high conductivity, mechanical hardness and environmental friendliness. Unfortunately, the Si/FeSi₂ nanocomposites are mainly prepared by high-energy ball milling, which has some drawbacks such as low purity, large particle size, and uncontrollable morphology, making it difficult to achieve the commercial application. Porous silica derived from clay minerals is extensively investigated for the preparation of silicon nanoparticles by magnesiothermic reduction. In addition, porous silica has a large specific surface area, which facilitates the effective dispersion and loading of iron oxides. The reduction of iron oxide and silica dioxide to Fe and Si can be achieved by magnesium. In this paper, a natural montmorillonite (Mnt) with a high content of silica (65%, in mass) was utilized as a raw material. Silicon/iron silicide (Si/FeSi₂) nanocomposites were synthesized via modification of Mnt (including acid etching and iron loading) and molten salt-assisted magnesiothermic reduction.

A porous silica (SiO₂) was prepared via leaching Mnt at a high concentration of HCl. Subsequently, a iron oxide was loaded on SiO₂ via precipitation in different Fe/Si mass ratios (i.e., 0, 10%, and 20%). Modified SiO₂ (Fe-SiO₂) was mixed with Mg and NaCl in a mass ratio of 1.00∶0.85∶3.00. Afterwards, the mixture was heated in an inert atmosphere at 650 ℃ for 5 h in a heating rate of 5 ℃/min. After cooling naturally, the product was washed with 1 mol/L HCl and 1% (in mass) HF in sequence to remove the by-product. Finally, it was rinsed with ultra-pure water until neutral and dried at 80 ℃. The sample were named as Si, Si/FeSi₂-1, and Si-FeSi₂-2, corresponding to the Fe/Si mass ratio of 0, 10%, and 20%, respectively.

The XRD patterns show that Si/FeSi₂ nanocomposites are consisted of Si and ɑ-FeSi₂. An increase in Fe content in precursors leads to a higher α-FeSi₂ content in the product. Based on the results of RIR value method and elemental composition analysis, the mass ratio of FeSi₂ to Si in Si/FeSi₂-1 and Si/FeSi₂-2 is 5% and 10%, respectively. The average grain sizes of Si, Si/FeSi₂-1, and Si/FeSi₂-2 are 20, 40 nm, and 48 nm, respectively, according to Scherrer's equation,. The grain size of silicon increases with the augmentation of Fe content in the precursor. This phenomenon analyzed by both transmission electron microscopy and scanning electron microscopy images is since the melting temperature of silicon nanoparticle is lower than that of bulk silicon (~1 410 ℃), the addition of iron greatly increases the local temperature (ΔH_Fe2O3= -309 kJ/mol vs. ΔH_SiO2= -130 kJ/mol), and the addition of Fe can effectively reduces the melting point of nanocrystalline grains in Fe/Si eutectic alloys. Moreover, the specific surface areas of Si, Si/FeSi₂-1, and Si/FeSi₂-2 are 89, 42 m²/g, and 33 m²/g, respectively. The gradual decrease in specific surface area coincides with the concurrent increase in grain size.

As anode electrodes, Si/FeSi₂ nanocomposites exhibit a higher initial coulombic efficiency, compared with Si due to the smaller specific surface area. The rate performance show that Si exhibits higher capacity than Si/FeSi₂-1 and Si/FeSi₂-2 at a low current density of 0.1 A/g. However, when the current density increases gradually, the capacity of Si is lower than that of Si/FeSi₂-1 and Si/FeSi₂-2. This phenomenon indicates that the incorporation of ɑ-FeSi₂ enhances both electron conduction and ion diffusion rates. After undergoing 500 cycles at a current of 1 A/g, the capacities of Si, Si/FeSi₂-1, and Si/FeSi₂-2 are 417, 781 mA·h/g, and 561 mA·h/g, respectively. The corresponding capacity retention rates are 35%, 77%, and 50%, respectively. The cycling performance demonstrates that Si/FeSi₂ nanocomposites have a more robust structure, compared to the Si electrode. In addition, the cyclic stability of Si/FeSi₂-1 is inferior to that of Si/FeSi₂-2, potentially due to the reduced structural stability resulting from a larger particle size.

The Si/FeSi₂ nanocomposites were prepared via modification of montmorillonite and molten salt-assisted magnesiothermic reduction. This method utilized magnesium powder to reduce Fe₂O₃ and SiO₂ for the in-situ formation of Si/FeSi₂ nanocomposites. The composition of Si and FeSi₂ nanocomposites could be adjusted via altering the ratio of Si/Fe in the precursor. Moreover, the reduction of Fe₂O₃ resulted in an increase in grain size and a decrease in specific surface area of silicon nanoparticles. As anode materials, Si/FeSi₂ composites demonstrated the superior rate performance and cycle stability, compared to Si. This phenomenon could be due to the incorporation of ɑ-FeSi₂, effectively enhancing the kinetics of lithium ions and electrons on the electrode. In addition, as an inert substance, FeSi₂ could reduce the volume expansion effect of silicon, thereby maintaining the stability of electrode structural. The structural stability of the Si/FeSi₂-2 electrode was relatively weaker than that of the Si/FeSi₂-1 electrode. Therefore, Fe content in the precursor could be of paramount importance for achieving high-performance silicon-based nanocomposite anodes.

The gyroscope operation relies on the electrostatic actuation and capacitance detection between the resonator and the planar electrode, with a typical gap ranging from 20-150 µm. When organic impurities adhere to planar electrode's surface, gap's capacitance changes, leading to fluctuations in the excitation detection signal and thereby affecting the accuracy and reliability of the gyroscope. TiO₂ thin film can effectively degrade organic pollutants through photocatalytic reactions. However, little research on its application on the surface of high-precision devices has been reported yet. The thickness of the TiO₂ thin film affects the generation and effective separation of photo-generated electron-hole pairs, thereby influencing the photocatalytic performance of the TiO₂ thin film. It is thus necessary to determine the thickness of the TiO₂ thin film on the surface of the planar electrode through experiments. In this paper, a TiO₂/Au composite thin film was designed to reduce the adsorption of organic substances on the surface of planar electrode and improve the thin film quality on the planar electrode surface.

TiO₂ thin films with different thicknesses were prepared on fused quartz substrates via radio frequency magnetron sputtering. The films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), UV-visible spectrophotometry (UV-Vis), and photocatalytic reaction analysis. The crystalline structure, grain size, surface morphology, and optical absorption characteristics of the TiO₂ thin films were analyzed to assess their impacts on the photocatalytic performance. The optimal thickness of the TiO₂ thin film suitable for the surface of the planar electrode was determined to be 240 nm. Finally, the planar electrode with a TiO₂/Au composite thin film was fabricated. The surface film layer of the planar electrode was characterized by nanoindentation, nano-scratching, and photocatalytic reaction equipment. The exceptional performance of the TiO₂-coated planar electrode in terms of adhesion, friction resistance, and photocatalytic self-cleaning properties was validated. The final step involved assembling the prepared flat electrode with a hemispherical resonator and using a capacitance meter to validate the superior performance of the TiO₂/Au composite film structured planar electrode for reducing the impact of organic impurities on the gap capacitance between the resonator and the planar electrode.

The XRD patterns show that the crystalline integrity and grain size of the film gradually increase as the thickness of TiO₂ thin film increases. The SEM and AFM images reveal that the surface roughness increases with the enlargement of grains as the film thickness increases. Based on the analysis of the properties of the TiO₂ thin film, TiO₂ thin film with a thickness of 240 nm exhibits the smallest bandgap width and the optimal photocatalytic performance. For the mechanical properties of the surface film layer on the planar electrode, the abrasion resistance of the planar electrode coated with the TiO₂ thin film is higher than that of the electrode uncoated with the thin film. Also, the adhesion between TiO₂ thin film and Au film on the surface of the planar electrode is comparable to the adhesion between Au film on the surface of the uncoated planar electrode and the substrate. The planar electrode undergoes photocatalytic self-cleaning experiments, TiO₂/Au composite film structured flat electrode can reduce the impact of organic impurities on the capacitance uniformity between the resonator and the flat electrode, thereby contributing to the enhanceed performance of the hemispherical resonant gyroscope.

The crystallinity, grain size, and surface roughness of the TiO₂ thin film increased with increasing TiO₂ film thickness. The TiO₂ thin film with a thickness of 240 nm exhibited the smallest bandgap width and appropriate grain size, thus demonstrating the optimal photocatalytic activity. The experimental verification of mechanical, photocatalytic, and capacitive performance of planar electrodes coated with TiO₂/Au composite films revealed that the adhesion of the TiO₂ thin film on the planar electrode met practical application requirements. Leveraging the excellent hardness and elastic modulus of the TiO₂ thin film significantly enhanced the abrasion resistance of the surface film layer on the planar electrode. Also, the efficiency of photocatalytic degradation of organic impurities on the planar electrodes coated with TiO₂ thin films was 1.6 times higher than that of the electrodes uncoated with the thin film. For assembling the prepared flat electrode with a hemispherical resonator and conducting capacitance meter testing, the TiO₂/Au composite film structured flat electrode could degrade organic impurities and reduce their impact on the gap capacitance between the resonator and the flat electrode under UV light exposure. It was evident that the TiO₂/Au composite film could have a promising practical application in the fabrication of resonant gyroscope flat electrodes.

β-Ga₂O₃ as a ultra-wide bandgap semiconductor material with a great development potential has a bandgap width of 4.8 eV, and a theoretical breakdown electric field of 8 MV/cm. Its Baliga advantage value of β-Ga₂O₃ is also several times greater than that of silicon carbide (SiC) or gallium nitride (GaN). However, the low thermal conductivity of β-Ga₂O₃ seriously affected the device's heat dissipation and the application in the high-power field. Wafer bonding is an indispensable key technology in semiconductor devices, which enables the formation of new structures, efficient fabrication, device integration, and cost reduction. The silicon substrate with the advantages of low cost and high thermal conductivity is an important substrate material for heterogeneous integrations. SiO₂ layer is easily formed on the surface of silicon, and the surface structure of SiO₂ consists of a Si-O-Si three-dimensional network structure together with an unsaturated Si-O structure, and the existence of this structure is conducive to reducing the probability of bubble generation, thus improving the quality of the bonding bonding interface, so it is easier to realize the bonding of silicon and β-Ga₂O₃ by using SiO₂ as an intermediate layer. This paper was to analyze the effect of O₂ plasma activation on the wafer surface, including changes in contact angle, roughness, and surface chemical composition. In addition, the effect of annealing temperature on the strength and thermal stability of the bond structure and the structure and composition of the β-Ga₂O₃/SiO₂ bond interface was also discussed.

SiO₂/Si substrate with the thickness of 550 μm and β-Ga₂O₃ single crystals sunstrate with the thickness of 650 μm were prepared. The two wafers were cleaned with alcohol and acetone via ultrasonic cleaning , and isopropanol for 10 min, then rinsed with deionized water and blown dry with N₂. Also, β-Ga₂O₃ and SiO₂/Si substrates were processed by oxygen plasma in a reactive ion etching (RIE) equipment (PlasmaPro 100 Cobra, Oxford Instrument Co., UK) at 50 mtorr and 300 W. The two activated wafers to be bonded were initially aligned and bonded, and pressure was applied to the wafer surface with tweezers to fully expel the gas from the bonding interface and make the bonding closer. Finally, the bonded wafers were placed on a pressurized platform for pressurized resting to complete the pre-bonding process. The pre-bonded wafers were placed in the annealing furnace for low-temperature annealing to enhance the bonding strength. A testing machine was used to determine the bond strength of the bonded pairs at different annealing temperatures. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to determine the bonded interface images and elemental distribution.

The contact angle and hydroxyl density with treatment time were investigated via adjusting the treatment time of O₂ plasma. The hydrophilicity of SiO₂ and β-Ga₂O₃ wafers greatly enhances, and the hydroxyl density on the wafer surface improves as the O₂ plasma activation time increases. O-H in β-Ga₂O₃ is produced by the breakage of oxygen atoms (O_w) in water that combines with surface Ga atoms (Ga_s) to form Ga_s-O_wH_w, and H combines with surface oxygen atoms (O_s) to form O_s-H_w. The effect of annealing temperature on the surface quality and bonding strength was also investigated. The results indicate that the bonding strength increases with the increase of annealing temperature. When the annealing temperature increases to 500 ℃, the bond strength increases to 7.31 MPa. However, this process leads to the cracking of the β-Ga₂O₃ substrate. Some cracks in β-Ga₂O₃ occur due to the thermal stress resulting from the different thermal expansion coefficients between SiO₂ and β-Ga₂O₃. β-Ga₂O₃ and SiO₂ surfaces are atomically bonded with no interfacial voids or cracks. The bonding interface's elements O, Ga, and Si are fully diffused during annealing.

In this study, a high-strength bonding of β-Ga₂O₃ and SiO₂ substrates was achieved at low temperatures via O₂ plasma activation. The FTIR analysis showed an increase in the hydroxyl density of the β-Ga₂O₃ and SiO₂/Si surfaces with the increase in plasma treatment time. The XPS and FTIR analysis demonstrated the changes in the hydrophilic functional groups on the surfaces before and after the plasma treatments. The bond strength gradually increased with the annealing temperature and reached 7.31 MPa, but unbonding and cracking also occurred at the edges of the bonded regions. The SEM and TEM images of the bonding interface demonstrated the existence of tight bonding between β-Ga₂O₃ and SiO₂ with full diffusion of elements Ga, O, and Si. In addititon, a model for direct bonding of oxygen plasma-activated β-Ga₂O₃/SiO₂/Si was also proposed.

Relying on their advantages of high water reducing rate, low dosage, and strong molecular structure design ability, polycarboxylate superplasticizers (PCEs) have become the most widely used admixture in the field of concrete admixtures. Adsorption of PCEs onto the surfaces of cement particles is the prerequisite for the dispersing performance of PCE molecules. Therefore, the influences of PCE molecules with different structures on the dispersion properties of cement slurry can be understood by revealing the adsorption process of PCE and the conformation characteristics of PCE after adsorption.

It should be noted that both the adsorption process and the conformation of the adsorbed PCE involve interfacial interactions between the organic and inorganic phases, which is the dominant factor determining the overall properties of the material. Recently, molecular dynamics (MD) simulations have been applied to the PCEs to elucidate its working mechanism. However, the molecular size of these model PCEs was much smaller than those typically used for industrial applications in order to reduce computation cost. Furthermore, only pure water was used, or only Na⁺, Ca²⁺ and Cl^- were additionally added to mimic a cement pore solution. The above methods make the results unable to accurately reflect the adsorption mechanism of PCE. Therefore, to better understand and effectively control the performance of PCE, more in-depth studies at the atomic and molecular scales are needed. Our research team innovatively used MD simulations in which the molecular size of the model PCE is consistent with that of PCE commonly used for industrial applications and simulates cement pore solutions. In addition, the adsorption mechanism of sulfonation modification of PCE was studied by combining the structure, dynamics and stability of interfacial connections.

The MD simulations used the Gromacs-4.6.7 software package and a conventional oplsaa force field with RESP charges. The UFF force field was used for the substrate. The equilibrium MD simulation was conducted under the NPT ensemble for a total run time of 20 ns at a relaxed liquid configuration (25 ℃). The solution environment simulations were performed using 3000 water molecules. A relaxation system was selected and the energy was minimized by the steepest descent method with a termination gradient of 100 kJ/(mol∙nm) before the relaxation. The system temperature maintained constant through a Nosé-Hoover thermostat, and periodic boundary conditions were applied to all three dimensions. Long-range electrostatics within a relative tolerance of 1×10^-6 is calculated by the particle mesh Ewald method and a cut-off distance of 1 nm was used as the Ewald interaction and van der Waals interactions. The bond lengths of hydrogen atoms were constrained by the LINCS algorithm. A leap-frog algorithm was used with a time step of 1 fs.

Under cement solution conditions, the side chains of PAA-g-PALS molecules were not entangled with the backbone (present a network-like conformation), while a small part of the side chains of PAA-g-HPEG molecules will curl onto the backbone (most of the side chains curled into a mushroom shape). In addition, the rotation radius of PAA-g-PALS (7.8 nm) was significantly larger than PAA-g-HPEG (7.1 nm) due to the large amount of —SO₃^- with strong electrostatic repulsion.

Part of the backbone of PAA-g-HPEG was adsorbed to the particles (the side chains curl and wrap the backbone), while PAA-g-PALS was adsorbed to the substrate surface by the "flat" mode of the individual side chains (the backbone and other side chains extend into the solution). Compared with PAA-g-HPEG, the binding point of sulfation modified PCE and the substrate is relatively scattered and increases the binding surface with the substrate, which is consistent with the calculation of binding force PAA-g-PALS (174.3 kJ/mol)> PAA-g-HPEG (134.5 kJ/mol).

The vertical heights of the individual PAA-g-HPEG and PAA-g-PALS molecules on the substrate surface were 6.8 nm and 19.7 nm, respectively, and the coverage rate was 26.4% and 21.2%, respectively. When considering the polymer cross-dimensions parallel and perpendicular to the particle surface, the penetration volume formed by PAA-g-PALS on the substrate surface increased by 132.64% relative to PAA-g-HPEG.

The main conclusions of this paper are summarized as following. PAA-g-HPEG and PAA-g-PALS tend to be comb and network conformations in cement slurry environment, respectively. Sulfonated modification dispersed the distribution of binding points between PCE and the substrate, improved the binding force between PCE and the substrate, extended the polymer far away from the substrate, and significantly increase the permeability volume (by about 132.64%). The present results not only provide new insights into the action mechanism of PCE at the atomic level, but also provide a theoretical basis for promoting the development of high performance cement-based materials.

White light emitting diodes directly driven by alternating current (AC-LEDs) become increasingly popular in lighting. However, the harmful flicker occurs because the blue LED chips only work over the threshold voltage. Transparent afterglow phosphor-glass composites are thus proposed as excellent color converters to eliminate the flicker. In this paper, Gd_2.94Al₂Ga₃O₁₂:0.06Ce³⁺-SiO₂ (GdAGG:Ce-SiO₂) glass ceramics were prepared via cold isostatic pressing molding and pressureless sintering at a low temperature. The transparency, structures, microscopic morphologies and luminescence properties were investiagted. Besides, the samples were assembled on the commercial blue LED chips or blue laser diodes (LDs) to explore the potential application.

For the preparation of GdAGG:Ce phosphor, stoichiometric Gd₂O₃, Al₂O₃, Ga₂O₃ and CeF₃ (99.9%) were weighed and placed in a mortar. After fully ground for 30 min, the obtained powder was transferred into a 20 mL corundum boat and placed in a tube furnace. The gas flow of 95%N₂/5%H₂ (in volume ratio) was introduced, and the temperature was hold at 1 450 ℃ for 4 h. After cooling to room temperature, the powder was ground in a mortar.

For the preparation of GdAGG:Ce-SiO₂ glass ceramics, 0.9 g GdAGG:Ce phosphor and 9.1 g amorphous SiO₂ nanoparticles were weighed and fully ground in a mortar for 30 min. The obtained powder was sieved with a 200 mesh standard sieve. Then, 0.8 g sieved powder was poured into a stainless-steel mold with an inner diameter of 20 mm, and pressed at 40 MPa for 30 s. The obtained blocks were placed in a cold isostatic press and kept at 250 MPa for 5 min. The green compacts were sintered in a muffle furnace in air at 600-800 ℃ for 5 h. After cooling down to room temperature, the samples were double-side polished.

For the preparation of lighting devices, Gd₃Al₂Ga₃O₁₂:Ce-SiO₂ glass ceramics of different thicknesses were encapsulated on the surface of 1 W commercial 450 nm LED lamp to assemble white LED devices. Besides, 1.0 mm thick Gd₃Al₂Ga₃O₁₂:Ce-SiO₂ glass ceramic was excited by a power-adjustable 450 nm laser to simulate a reflective white LD device.

The translucent GdAGG:Ce-SiO₂ glass ceramics are yellowish green, and the color becomes lighter with increasing sintering temperature. The transmittance of glass ceramics (1.0 mm thickness) in the visible region is approximately 60% due to the mismatch of refractive index between GdAGG:Ce phosphor and SiO₂. The X-ray diffraction patterns show that the glass ceramics exhibit both bulge peak of glass phase and diffraction peaks of Gd₃Al₂Ga₃O₁₂ (JCPDS 46-0448). The scanning electron microscopy images and laser scanning confocal microscopy images indicate that GdAGG:Ce phosphor powders with the sizes of 1-10 μm are uniformly dispersed in SiO₂ glass matrix. The transmission electron microscopy image indicates that the interfacial reaction is well suppressed at a low sintering temperature.

Under 450 nm excitation, the glass ceramics show typical Ce³⁺: 5d₁→4f broadband emissions peaked at 536 nm, whose luminescence characteristics are similar to those of GdAGG:Ce phosphor. The luminescent intensity firstly increases and then decreases, reaching the maximum value at 700 ℃. After removing the excitation source, the glass ceramics show a bright yellowish green afterglow. The longest afterglow appears from GdAGG:Ce-SiO₂ glass ceramic obtained at 700 ℃. Besides, the lifetime when the afterglow intensity decays to 80% of initial one is 27 ms, which meets a requirement of AC-LED devices (no less than 0.4 ms).

The internal quantum efficiency of glass ceramics is 63%, which meets the practical application standard of white LED devices (no less than 60%). The emission intensity at 150 ℃ maintains 85.3% of that at room temperature, indicating that the glass ceramics have an excellent thermal stability.

In coupling the glass ceramic with a 450 nm blue chip, the resulting white LED device exhibits a luminous efficiency (LE) of 81.7 lm/W, a correlated color temperature (CCT) of 5 805 K and a color rendering index (CRI) of 70.8 when driven by 150 mA direct current (DC). Besides, the flicker index decreases to 68.9% when driven via alternating current (AC). Coupled with a 450 nm blue laser, the white LD device shows the LE of 132.6 lm/W, the CCT of 6 528 K and the CRI of 70.6.

Translucent GdAGG:Ce-SiO₂ glass-ceramics were prepared via cold isostatic pressing and low temperature sintering (i.e., 700 ℃/5 h). The self-made GdAGG:Ce afterglow phosphor was uniformly embedded in SiO₂ glass matrix. The glass ceramic retained the luminescent properties of GdAGG:Ce phosphor due to little interfacial reaction. The glass ceramic exhibited a broad emission band peaked at 536 nm, whose quantum efficiency was 63% after excited at 450 nm. The emission intensity at 150 ℃ was 85.3% of that at room temperature. Besides, the glass ceramic exhibited a bright yellowish green afterglow, and the lifetime was 27 ms when the intensity decayed to 80% of initial one. The glass ceramic based white LED device had the LE of 81.7 lm/W, the CCT of 5 805 K, and the CRI of 70.8 when driven by 150 mA DC, and the flicker index reduced to 68.9% when driven by AC. The white LD device showed the LE of 132.6 lm/W, the CCT of 6 528 K and the CRI of 70.6. The results indicated that GdAGG:Ce-SiO₂ glass-ceramic could have a great application potential for AC-LEDs.

As a kind of high-energy electromagnetic radiation, gamma rays can lead to radiation effect and environmental pollution. To ensure the reliability and safety utilization of gamma radiations in different areas, materials with reliable gamma shielding performances should be developed. The existing efforts are to use glasses as alternative for the conventional radiation shielding materials. As a typical window material, glass itself has attracted wide attention due to its unique chemical and physical advantages. Among them, lead-based radiation shielding materials are widely used in the field of ionizing radiation protection due to their reliable physical properties. In the nuclear industry and high energy physics laboratories, different materials can be used for temporary or permanent shielding. The lead-based glass doped with heavy metal oxide PbO is widely used in the field of radiation shielding for a long time with reliable light transmission properties, which facilitates the observation and monitoring of radiation areas. In this paper, three kinds of transparent silicate glass with different PbO contents were prepared by a high-temperature melting forming method. The gamma-rays protection abilities of the three kinds of glass were investigated through experimental and thermotical methods. The chemical and thermal stability of the glass were also analyzed. In addition, the influence mechanism of the structure and performance differences of the three kinds of glass was also discussed.

Analytical pure quartz sand (SiO₂, purity 99.5%, in mass, the same below), lead monoxide (PbO, purity 99.0%), potassium nitrate (KNO₃, purity 99.0%) and sodium nitrate (NaNO₃, purity 99.0%) were selected as raw materials for preparation of three kinds of gamma-rays shielding glass materials by a high-temperature melting method. An appropriate amount of raw materials was thoroughly mixed and added to 3 L quartz crucible and heated in air at 1 200 ℃. Then the raw materials were melted at 1 250 ℃ for 14 h. The uniform melt was quickly poured into the 150 mm×150 mm×50 mm stainless steel mold preheated at 750 ℃. Finally, the quenched glasses were annealed at 450 ℃ for 12 h and cooled naturally to room temperature.

The density of the three glass samples was tested based on the Archimedes principle. The thermal expansion coefficient of glass samples was measured by a model Netzsch DIL 402 expansion coefficient tester. The infrared spectra were measured by a model Perkinelmer Spectrum 100 FTIR Spectrometer. The Raman spectra were tested by a model HORIBA LabRAM HR800 high-resolution Raman spectrometer. The gamma ray shielding test was completed in China Academy of Engineering Physics. The chemical stability test was completed in Chengdu Guangming Glass Co., LTD. The acid stability and moisture stability of the glass samples were tested according to the national standards GB/T 7962.14-2010 and GB/T 7962.15-2010, respectively. The thermal stability of the galss was also determined.

Glass structure becomes more compact with the exchange of Pb alternatives of Si, K and Na. Increasing the density of glass is conducive to improving its shielding performance, but this leads to significant changes in the optical properties, thermal properties and chemical stability of glass due to the increase of heavy metal content. The preparation of high transmittance glass is more difficult. The coefficient of thermal expansion of glass samples gradually decreases from 103.6 × 10^-7 ℃^-1 to 89.2 ×10^-7 ℃^-1, and the values of T_g and T_f also decrease with the increase of mass fraction of PbO in glass components. The change of the thermal properties of the three glass samples is a result of the joint action of PbO, Na₂O and K₂O. The FTIR spectra show that the added PbO is transformed into [PbO₄] units with 4 coordination numbers into the network under the condition of sufficient free oxygen as PbO content in the glass increases. These [PbO₄] units participate in the formation of silicate networks. The Raman spectra indicate that the silicate network structure is de-polymerized as PbO content is increased, and the enhancement of the characteristic vibrational peaks corresponding to the Pb-Si-O indicates an increase in the degree of participation of the [PbO₄] units in the formation of silicate network. The ion packing density of the glass sample gradually increases with the increase of PbO content, which shows that the compressible free volume per unit volume of the glass sample becomes smaller. PbO with a high concentration (x = 0.50 and x = 0.66) is used as a glass-forming agent, and the [PbO₄] structural units can form a connection structure with the silicon oxide tetrahedron, which plays a role in repairing the glass network.

The permeability of the glass can be improved via strictly controlling the iron content of the introduced raw materials and making full use of the double alkali effect of the glass. The actual shielding performance of glass is not a result of simple addition of various components. This can be affected by the actual composition content of the glass, melting process and endoplasmic uniformity. The influence of glass expansion coefficient on the thermal stability is much greater than that on its chemical stability.

PbO with a high concentration (x = 0.50 and x = 0.66) was used as a glass-forming agent, and the [PbO₄] structural units could form a connection structure with the silicon oxide tetrahedron, playing a role in repairing the glass network. The measured shielding rate of ⁶⁰Co gamma-ray could be 50% and the glass with 50% PbO content (in mass fraction) exhibited a linear transmission rate of more than 85% in the range of 400-800 nm. In addition, the reliable thermal and chemical stabilities were also reflected in the glass.

The thermoelectric cooling technology has a potential in the field of refrigeration for 5G chips, infrared detector, and temperature controlling, etc.. To improve the efficiency of thermoelectric refrigeration and enhance the competitiveness of thermoelectric refrigeration technology, it is of great significance to develop high-performance thermoelectric refrigeration materials. However, the refrigeration temperature of the first-stage refrigerator is 230 K based on commercial Bi₂Te₃-based alloy, and the refrigeration temperature of the multi-stage refrigerator is as low as 150 K, while the thermoelectric performance of the commercial Bi₂Te₃-based alloy is sharply reduced at below room temperature, which is difficult to meet the needs of low-temperature refrigeration. It is thus necessary to develop high-performance low-temperature thermoelectric cooling materials to meet the low-temperature refrigeration in the future.

SiOC-based anode materials have a great potential for lithium-ion batteries, but the poor conductivity is the main problem that make it difficult to commercialize. The SiOC/C anode materials combine the high conductivity of carbon materials with some advantages of high capacity, stability, and mechanical flexibility of SiOC. Among them, SiOC/nanocarbon composite materials are developed due to their superior electrochemical performance. Although some progresses are achieved in the design of SiOC/C anode for the lithium-ion batteries, some challenges still remain in practical application. The main problems existing in SiOC/C anode materials are that the size of SiOC is larger, resulting in a lower utilization of active sites. The preliminary research conducted on nitrogen-doped carbon indicate that more active sites can be obtained via utilizing the defects. However, it is still necessary to explore the effect of other doping elements or through multi-component composites. To further enhance the feasibility of electrochemical performance, the lithium ions storage mechanism of SiOC anode materials still needs a further research. The detailed structure evolution of SiOC can be revealed during lithium ions storage process through some advanced in-situ characterization techniques. The lithium ions storage mechanisms can be further clarified, and, the electrochemical performance of SiOC-based anode materials can be improved more effectively. Improving the electrochemical performance and safety of lithium-ion batteries is a goal pursued by many researchers. Overcoming the above problems can lead to the widespread application of SiOC-based anode materials in high energy lithium-ion batteries, even in areas such as lithium sulfur batteries, sodium ion batteries, and potassium ion batteries.

The power generation of reforming CH₄ based on SOFC has great advantages in energy conversion efficiency, material flexibility and environmental protection. However, it faces some problems such as carbon accumulation and poor stability in practical application. At present, four typical anti-carbon anode materials, such as Ni-based anode doped with precious metals, CeO₂, barium oxide and Ni-free anode, can effectively improve the anti-carbon stability. Although these materials show a good carbon resistance, they have some problems such as high cost of precious metals, easy sintering of cerium oxide, poor chemical stability of barium oxide and low catalytic activity of Ni-free anode. Improving SOFC operating conditions and optimizing anode materials (i.e., modification of existing catalysts, design of anode microstructure and eforming catalysts) are the keys to achieving the efficient and stable reforming of methane. The development of anode catalysts with low cost, high chemical and mechanical stability, anti-coking and high catalytic activity is an urgent need for sustainably converting carbon-based fuels by SOFC. In addition, the internal anode elementary reactions involved in the process of SOFC reforming methane are complex and mostly exothermic reactions, accompanied by a large amount of heat generation, so it is also necessary to conduct electrochemical and thermodynamic coupling studies, combined with cogeneration technology to further improve energy conversion efficiency. In summary, it is still necessary for the commercial development of green power generation by CH₄-based SOFC to investigate the influence mechanism of CH₄-based SOFC reforming reaction, anode catalyst material optimization, and develop new research directions.