It is well known that crude oil is one of the most important energy sources. The oil-in-water emulsion is often produced during oil exploitation due to waterflooding and groundwater. This emulsion causes damage to the transmission pipeline and environment. Therefore, the separation of oil and water is an essential step in the petroleum industry. Chemical demulsification is currently the most widely employed due to its convenient operation and quick response. However, the extensive use of chemical emulsifiers has brought potential harm to the environment, so it is necessary to explore novel environmentally friendly demulsifiers. Recently, nanoparticle (NP) demulsifiers have been widely concerned in the application of demulsification for crude oil emulsion. NP demulsifiers usually refer to chemically synthesized nanoparticles or modified natural nanoparticle minerals. While graphene oxide and reduced graphene oxide are reported to exhibit an excellent demulsification performance of more than 99.9%, the high cost of raw materials limits their widespread use. As a result, economical mineral materials such as attapulgite, kaolinite, and nano-silica are employed to develop NP demulsifiers.

Ordinary mineral nanomaterials typically consist of a single hydrophilic part (e.g., quartz, silicate, etc.). Therefore, they require complex surface modifications to adjust their hydrophilicity and hydrophobicity, enabling them to be excellent demulsifiers. Recently, researchers found a novel mineral material called Micro-nano silicon-carbon ore (Si-C). The Si-C particles consist primarily of hydrophilic quartz and hydrophobic carbon, so it is expected that they can be used to prepare a novel NP demulsifier.

The Nano silicon-carbon ore utilized was sourced from a mining site named Shilukeng in Fengcheng City, Jiangxi Province, China. Initially, bulk samples of Si-C were ground, and the resulting mineral particles were subsequently screened to obtain samples less than about 1 um. The demulsifiers (OSi-C) were prepared through a simple oxidation treatment.

The major elemental composition of the Si-C includes O (40.35%), Si (35.33%), C (9.15%), Al (2.18%), Fe (1.3%), K (0.33%), and the loss on ignition is 9.57%. The average particle size of Si-C was 343.4 nm. The Zeta potential of OSi-C was considerably lower than that of the Si-C for all pH conditions. This is due to the introduction of oxygen-containing functional groups on the OSi-C surface after oxidation treatment. The content of C-OH, C-O-C, and O=C-O increased compared to that of the Si-C, suggesting that the OSi-C was successfully oxidized, resulting in increasing oxygen-containing functional groups. After oxidation, the obtained OSi-C nanoparticles showed good amphiphilicity, interfacial activity, and low interfacial tension (IFT) properties, which enable the particles easily to arrive at the oil-water interface. And it was believed that the self-assembly behavior of OSi-C at the oil-water interface is due to its good interfacial activity and the ability to reduce the oil-water IFT. At a demulsifier dosage of 1000 mg/L, OSi-C exhibited a demulsification efficiency exceeding 98.94% at pH 6, with the oil concentration in the separated water less than 97.33 mg/L.

An OSi-C nanoparticle demulsifier was prepared by a simple oxidation treatment of natural Si-C nanoparticles to achieve highly efficient demulsification for the crude oil-in-water emulsion at room temperature (25 ℃). The OSi-C nanoparticles exhibit superior demulsification performance than the original Si-C at the optimal conditions, and have a demulsification efficiency of 98.94% at pH 6. The mechanism behind emulsion breaking was revealed through analyses of Zeta potential, interfacial activity, surface wettability, dynamic IFT, self-assembling at the oil-water interface, and microscopic observation of the demulsification process. On the one hand, the OSi-C nanoparticles have good amphiphilicity, interfacial activity and the ability to self-assembly at the oil-water interface, which makes it easy to arrive at the oil-water interface. On the other hand, the OSi-C material has abundant Oxygen-containing functional groups and aromatic ring structures, which can promote the binding of nanoparticles with emulsified molecules of asphaltenes and resins at the oil-water interface through hydrogen bonding and π-π interactions. Furthermore, with the help of external forces such as stirring and oscillation, the protective film at the oil-water interface ruptures, thereby achieving oil-water separation. Therefore, the OSi-C nanoparticles can rapidly break the emulsion with high efficiency at room temperature. Due to the natural composition advantage and nontoxicity of the raw Si-C, this work provides a new approach for synthesizing environmentally friendly natural mineral NP demulsifiers.

Hardness testing is crucial for evaluating the mechanical properties of ceramics, especially in applications involving wear and scratch resistance. The widely used Vickers hardness test is often affected by an indentation size effect (ISE), resulting in hardness values deviating from their true values under lower loads. Moreover, significant discrepancies in hardness values obtained between the Vickers hardness testers and micro-/nano-indentation instruments at low loads for identical samples persistently cause a confusion. The conventional theories presume that the ceramic materials' indentation dimensions remain unaltered before and after unloading. However, these dimensions often exhibit variations in practice. The existing models and methodologies fail to universally accommodate diverse materials, making it essential to clarify these issues for the accurate assessment of ceramic material hardness. This study was to explore the origins of the Indentation Size Effect (ISE) and the patterns of indentation deformation via comparing the Vickers hardness data with micro-/nano-indentation results under varying loads, thereby furnishing a theoretical foundation for the standardization of ceramic hardness testing.

Three representative ceramic materials (i.e., Al₂O₃, ZrO₂, and (Hf_0.5Zr_0.5)C) were investigated to evaluate their load-dependent mechanical responses. After being sequentially sectioned, ground, and polished, the specimens were subjected to a series of Vickers hardness tests at different loads. The Vickers hardness values were determined via optically measuring the diagonal dimensions of residual indentations using a metallographic microscope. Simultaneously, micro-/nano-indentation tests were performed by a nanoindenter equipped with a Vickers indenter. The pre-unloading hardness values were calculated based on the changes in depth after loading. Subsequently, the post-unloading hardness values were obtained via measuring the indentation sizes after unloading using scanning electron microscopy (SEM). Through a comprehensive analysis of the variations in indentation sizes before and after unloading, this study could elucidate the characteristics of load-dependent mechanical responses in those ceramic materials.

The three ceramic specimens display pronounced load-dependent characteristics according to the Vickers hardness data. Three specimens exhibit significant hardness declines in a low-load regime (i.e., decreased by 3 4.44% for Al₂O₃, decreased by 22.85% for ZrO₂, and decreased by 29.44% for (Hf_0.5Zr_0.5)C), and stabilize at characteristic plateau values (i.e., 15.6 GPa, 12.9 GPa, and 18.6 GPa, respectively) beyond critical threshold loads (i.e., 3-5 N) as the load increases. This behavior is attributed to the predominance of elastic recovery mechanisms during low-load indentation, which results in measured values that exceed the true hardness of the materials. As the load further increases, the plastic deformation becomes a dominant mechanism, leading to stabilized indentation dimensions and hardness values that more accurately reflect the intrinsic properties of the ceramics.

A comparative study is conducted to evaluate the pre-unloading hardness values derived from depth changes during loading and the post-unloading hardness values calculated from residual indentation dimensions as using the micro-/nano-indentation system. This investigation reveals three distinct types of indentation behavior among the materials tested. For Al₂O₃, the Vickers hardness tester obtains significantly higher results than the micro-/nano-indentation tester at low loads. This discrepancy is since the indentation diagonal exhibits a rebound pattern after unloading, resulting in a minimal residual deformation and consequently an overestimated hardness value. In contrast, ZrO₂ demonstrates the opposite trend. Ceramic materials exhibit a localized microplastic deformation at indentation edges. For ZrO₂ under low loads, the phase transformation-induced expansion at an indentation periphery creates an extrusion effect, increasing residual indentation dimensions and resulting in extrusion-type morphology. The results of Vickers hardness values measured by the tester that are lower than those obtained from micro-/nano-indentation tests. For (Hf_0.5Zr_0.5)C, a stress is alleviated due to the formation of micro-cracks around the indentation. Since there is no significant change in indentation size after unloading, the testing methods both yield comparable hardness results.

A further analysis indicates that minor deviations in indentation size (Δd) have a significant effect on the low-load hardness calculations. For instance, in the case of ZrO₂ at a load of 0.01 N, a small Δd of only 0.24 μm can lead to a relative error of 20%, due to the extremely small indentation size of 1.20 μm, which results in a substantial 57% deviation in hardness measurements. The critical load is the threshold above, which the plastic deformation dominates and elastic recovery is negligible, leading to stable test results. The differences between the results by the Vickers hardness testers and by the micro-/nano-indentation testers can be attributed to several factors, i.e., a) indenter precision: Nano-indenters have sharper tips, allowing for more accurate contact area calculations at low loads; b) load range: Nano-indenters are designed for ultralow loads (< 1 N), but are more prone to ISE. The Vickers testers require loads of 5 N or greater to minimize errors; and c) test objective: Nano-indentation primarily reflects the properties of individual grains, while Vickers testing reflects a combined response of multiple grains and their grain boundaries. These factors contribute to the differences in hardness results obtained from the two testing methods, highlighting the importance of choosing an appropriate technique based on the specific material characteristics and testing goals.

For reliable mechanical characterization of advanced ceramics, an empirical minimum applied load of 5 N was established as a critical threshold in Vickers hardness testing. This threshold was essential for eliminating load-dependent artifacts and ensuring the reproducibility of measurements. This protocol effectively suppressed elastic recovery contributions to indentation work, obtaining the hardness values that accurately reflected a bulk plastic deformation behavior. Three distinct indentation morphologies were categorized based on the systematic analysis of dimensional recovery characteristics, a) stable type: This could align with conventional assumptions regarding indentation behavior; b) rebound type: This morphology resulted in higher Vickers hardness values due to the rebound effect during unloading; and c) extrusion type: This morphology resulted in lower Vickers hardness values. At low loads, elastic deformation could dominate, while plastic deformation could remain minimal. This scenario caused the calculated hardness that was greater than the true value. As the load further increased, the irreversible residual indentation size became significantly larger than the minor elastic recovery deformation, leading to a stabilization of the calculated hardness value. This phenomenon could be a primary reason for the load effects obtained in hardness testing.

Functional coal-based carbon materials demonstrate an enormous application potential in the field of electrochemical energy/matter conversion and storage due to their abundant raw materials, low cost, and adjustable structure. This review systematically summarizes the research progress on the preparation methods and electrochemical applications of functional coal-based carbon materials, and explores the intrinsic relationships between material structure and electrochemical performance. Based on the existing research status of the preparations and electrochemical applications of functional coal-based carbon materials, we propose some prospects for their future research directions, i.e., 1) Simple and environmental-friendly physical activation methods need to be developed, such as supercritical CO₂-assisted activation and microwave carbonization, which achieve controllable pore structure construction through radical reactions and interfacial energy regulation. Low-energy technologies such as photothermal-driven carbonization and plasma pulse activation should be developed to utilize non-equilibrium thermodynamics to regulate the degree of graphitization and defect quantity of carbon layers, thereby reducing carbon emissions from the preparation process. In addition, machine learning can be also used to optimize preparation parameters (such as temperature field, pressure field, atmosphere composition, etc.) to achieve accurate prediction and targeted control of materials' morphology, structure, and chemical composition, 2) The structure-property relationship and performance improvement mechanism of materials need to be analyzed. In-situ characterization techniques (such as electrochemical-synchrotron radiation coupling technology and in-situ aberration-corrected electron microscopy) can analyze the material structure and composition during electrochemical processes, clarify the mechanisms of material performance degradation under complex conditions, and develop modification strategies. In addition, it is also necessary to develop kilowatt-scale industrial electrochemical devices suitable for functional coal-based carbon materials to promote the practical application of coal-based carbon materials and 3) Some precise coal quality analysis methods and standardized coal processing methods need to be establised and the continuous, large-scale production equipment needs to be developed, thereby addressing the impact of coal raw materials on product structure and performance consistency. For instance, establishing a rapid analysis of coal quality (i.e., combining near-infrared spectroscopy with Raman spectroscopy)-three-dimensional structural simulation (i.e., Material Studio)-process parameter feedback system ensures that the structural parameters of coal raw materials from different production areas remain within a certain range. The design of a modular mobile doping-activation-pyrolysis integrated system is expected to enable the continuous conversion of coal raw materials into functional coal-based carbon materials, thus addressing the impact of conventional batch preparation process on the product performance. These technologies can contribute to the large-scale production and application of high-performance functional coal-based carbon materials.

Hard optical fiber imaging components as two-dimensional array imaging materials comprised of tens of millions to billions of micro- and nano-scale optical glass fibers have extensive applications in numerous optical systems, including low-light-level image intensifiers and space target detection systems. Resolution and contrast are crucial indicators affecting the performance of these components. Elemental diffusion at the core-clad interface results in a gradient distribution of material refractive index rather than the ideal abrupt distribution, thereby degrading the resolution and contrast of the components. It is necessary for the demands for refined manufacturing processes of these components to gain a comprehensive understanding of the diffusion behavior and distribution status of elements at the core-clad interface. At present, energy dispersive spectrometry (EDS) is often employed as a characterization tool for elemental distribution status, yet it suffers from a low image resolution (20 nm) and lacks corresponding quantitative calculation methods. In this study, high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) was utilized to acquire high-precision images of elemental spatial distribution. Furthermore, a multi-model fusion machine learning approach was proposed to address the challenges of characterization and quantitative analysis in the study of elemental migration at the core-clad interface of hard optical fiber imaging components.

In this study, monofilaments undergoing various thermal processes were fabricated by a drawing technique. High-Angle Annular Dark-Field (HAADF) images were captured and utilized to train Tree-SVM/LDA models. These models enabled pixel-level core-clad classification and x-y two-dimensional spatial classification, thereby yielding quantitative results on elemental interface diffusion. In addition, the reliability of the models was also analyzed.

The Tree-SVM/LDA model is grounded on the following assumptions, i.e., element Si as a key component in the formation of both core and cladding glass network structures remains stable during the diffusion process. The deviation distances of other elements are benchmarked against that of Si, the average deviation (D) is defined as an arithmetic mean of the migration distances of all elements within the tested range, serving to characterize the overall diffusion behavior of elements rather than individual extreme values, elements undergo unidirectional migration, consistent with the direction of the concentration gradient, manifesting as the perpendicular direction to the interface in monofilament samples, the transition zone at the core-cladding interface is formed through the superposition of diffusion behaviors of different elements, and the algorithmic procedure of model encompasses the following steps (i.e., constructing training and prediction datasets; training the decision tree model; developing a labeled prediction dataset; and obtaining classification hyperplane parameters).

The results obtained by SVM and LDA models both indicate the thermodynamic principles at higher resolutions, with the deviation D_K∈[10, 40]nm, D_Ba∈[0, 11]nm, and D_Ti∈[0,13]nm. At lower resolutions, where the width of a single pixel in the raw data is 3 nm, the computational error of the models is amplified threefold, leading to the results that deviate from actual principles. At 810 ℃, the SVM model exhibits a poor data separability due to the low content of Ti in the cladding region, resulting in abnormal calculation results. This phenomenon underscores the superiority of the LDA model over SVM in terms of training set diversity, demonstrating a greater generalization capability. The calculation results of the SVM model and LDA model show a good consistency, while also presenting regular differences, i.e., the boundaries obtained by the LDA model tend to skew towards the cladding region relative to those of the SVM model. This regularity may be associated with differences in model characteristics and the element distribution patterns in the HAADF images of the core and cladding regions, having a further in-depth research. In general, the SVM model achieves higher accuracy than the LDA model. However, the LDA model possesses a better generalization capability.

The migration capabilities of the elements K, Ti, and Ba intensified as the wire drawing temperature increased. Specifically, the average migration distance of element K could range from 10 nm to 40 nm, while that of elements Ti and Ba could span from 0 to 13 nm. Affecting the reliability of models were since the spatial resolution of the raw data could be in atomic or sub-atomic scale, models could be sensitive to data anomalies, thus requiring repeated training, elements with great diffusion capabilities could decrease the accuracy of the model, while simultaneously enhancing its generalization capability. The SVM model demonstrated superior accuracy, compared to the LDA model, having a weaker generalization capability. The SVM model could be recommended at a high quality of the raw data, whereas the results of the LDA model could be more realistic at a low quality of the raw data.

Building a clean, low-carbon, safe, and efficient energy system and implementing renewable energy substitution actions become important issues to promote sustainable energy utilization. As a representative of clean and sustainable energy, the use of solar energy can greatly reduce carbon emissions, while meeting the growing demand for energy consumption. Since 2009, CH₃NH₃PbI₃ perovskite has been used as a light absorbing layer, achieving a photoelectric conversion efficiency of 3.8%. The organic-inorganic hybrid perovskite material has attracted much attention as a solar cell light absorbing material. However, lead halide perovskite materials are highly susceptible to various external environmental factors such as dopants, heat, light, humidity, etc., which can cause failures in the chemical or physical structure during their application, greatly restricting the commercial application of the devices. It is thus of great significance for the practical application of lead halide based perovskite devices to investigate the intrinsic relationship among the structure, properties and stability. This study employed methylammonium (CH₃NH₃⁺, MA), formamidinium (CH (NH₂)₂⁺, FA), and Cesium (Cs) as A-site ions to construct three perovskite configurations (i.e., MA_1-xFA_xPbI₃, MA_1-xCs_xPbI₃, and Cs_1-xF A_xPbI₃). The structure, stability, electronic and optical properties were investigated, and the theoretical basis for further experimental optimization and exploration of efficient and stable perovskite solar cell materials was also discussed.

The structure and optoelectronic properties of A-site modified lead halide A'_1-XA''_XPbI₃ (where A' and A'' are any of MA, FA, and Cs) perovskite configurations were investigated based on density functional theory by using CASTEP module under the Perdew Burke Ernzerhof exchange correlation functional of generalized gradient approximation via optimizing the structure and calculating the formation energy, band structure, density of states and absorption coefficient. After structural convergence testing, the energy cutoff of the plane wave was selected as 600 eV, and the Monkhorst-Pack scheme was used to mark the Brillouin zone by using a 2×3×2 k-point grid. The energy convergence standard of the system was set at 10^-5 eV/atom. The maximum force was limited to 0.03 eV/Å with the maximum stress of 0.05 GPa, and the maximum displacement of 0.01 Å.

The optimized crystal structures of MA_1-xCs_xPbI₃, MA_1-xFA_xPbI₃ and Cs_1-xFA_xPbI₃ (x=0.125, 0.250, 0.500) perovskite configurations show that the cell volume of Cs_1-xFA_xPbI₃ and MA_1-xFA_xPbI₃ increases while MA_1-xCs_xPbI₃ decreases with increasing the doping content due to the atomic distance of FA group with 3.996 A, MA group with 3.009 A and the radius of Cs⁺ only 1.88 A. Meanwhile, the doping ions at A-site can cause the distortion of Pb-I octahedron, resulting in variations on bond length, bond angle and torsion of octahedron, and MA_0.875FA_0.125PbI₃ demonstrates a slight distortion. The formation energy of MA_1-xCs_xPbI₃, MA_1-xFA_xPbI₃ and Cs_1-xFA_xPbI₃ configurations is negative. As the Cs/MA, FA/MA, and FA/Cs ratios increase, the formation energy becomes more negative, indicating the doped groups can enter the lattice spontaneously and smoothly. The formation energy of MA_1-xFA_xPbI₃ is minimum (i.e., -521.77, -1042.79 eV and -1824.49 eV correspond to x=0.125, 0.250 and 0.500), compared to that of MA_1-xCs_xPbI₃ (i.e., -492.58, -984.86 eV and -1722.95 eV) and Cs_1-xFA_xPbI₃ (-28.87, -57.79 eV and -101.61 eV), due to the large energy difference in MA and FA groups and the resulting strong force between atomic groups. This indicates that FA groups can enter MAPbI₃ lattice more easily and form a more stable structure. The energy band structure calculated shows that the conduction band minimum (CBM) and valance band maximum (VBM) of MA_1-xCs_xPbI₃, MA_1-xFA_xPbI₃ and Cs_1-xFA_xPbI₃ are located at the same high symmetric point G(0, 0, 0), thus determining direct band gap semiconductors. Furthermore, Pb 6p orbital and I 5p orbital dominate in CBM and VBM, respectively. Except that, the electron orbital of FA contributes to CBM significantly, mainly situating at 3.33 eV. The contribution of MA and Cs is primarily at -4.60 eV and 5.35 eV away from the Fermi surface, hence leading to a relatively large band gap in MA_1-xCs_xPbI₃. As for Cs_1-xFA_xPbI₃, Cs and FA orbital overlap at the conduction band (CB, 2.0-4.0 eV), and a great covalent bond can be formed between C-Cs, which facilitates the new energy orbital formed and thus more stronger orbital hybridization with Pb and I, and eventually in turn causes CB to shift upward and the band gap increases. However, compared with Cs, the interaction of MA and FA electron orbital at CB reduces, and MA_1-xFA_xPbI₃ shows a relatively small band gap. MA_0.875FA_0.125PbI₃ exhibits a decent band gap and a decreased energy band dispersion at CBM, promoting the transition of charge carriers and improving light absorption. Also, the real part of the dielectric functions ε₁(ω) peak for MA_0.875FA_0.125PbI₃ demonstrates a red shift from 533 nm to 572 nm, and ε₁(ω) is optimal with the increase of wavelength. The widened wavelength response range and high ε₁(ω) endow MA_0.875FA_0.125PbI₃ with an optimal light absorption capacity in the visible light range of 380-780 nm.

The optoelectronic properties of lead iodide-based perovskite A'_1-XA''_XPbI₃ were predicted by using first-principles via the structural optimization and the calculation of formation energy, band structure, density of states, absorption coefficient. The results indicated that MA, FA groups, and Cs ions could spontaneously enter the A-site of lead iodide A'_1-XA''_XPbI₃ perovskite to form a stable structure. Compared with MA_1-xCs_xPbI₃ and Cs_1-xFA_xPbI₃, MA_1-xFA_xPbI₃ configuration displayed a minimum distortion of Pb-I octahedral and a more stable structure. In addition to the contribution of I 5p orbitals to VBM and Pb 6p orbitals to CBM, the electronic orbitals of FA in the CBM resulted in a dramatical decrease in band dispersion, which was conducive to light absorption. The absorption peak of MA_0.875FA_0.125PbI₃ at 500nm showed a significant red shift. The widened wavelength response range and increased light absorption coefficient endowed MA_0.875FA_0.125PbI₃ with an optimal light absorption ability in the visible light range, making it a promising solar cell photovoltaic material.

Systematic statistical analysis reveals that distinct doping elements exert element-specific regulatory effects on the key performance metrics of layered oxide cathodes for sodium-ion batteries (i.e., capacity, rate capability, long-cycle stability, and structural integrity). Electrochemically inactive dopants enhance structural stability at the expense of reducing the number of redox-active sites due to lattice occupation, leading to capacity decay. Conversely, electrochemically active dopants improve capacity through redox reactions yet modify electron cloud distribution (i.e., exacerbating electronic disorder and altering localization/delocalization behavior), concurrently inducing lattice distortion and additional stress that compromise structural stability. Consequently, synergistic modification strategies integrating high-entropy design with doping effects emerge as a pivotal approach to transcend comprehensive performance limitations. However, this strategy confronts triple challenges, i.e., 1) synthesis requiring prolonged high-temperature annealing with precise multicomponent stoichiometric control, significantly amplifying manufacturing complexity and cost; 2) cost escalation from precious/rare-earth dopants restricting industrial scalability; and 3) insufficient mechanistic understanding of the synergistic interactions between dopant elements. A future research must prioritize developing low-cost facile synthesis techniques, advancing computational materials science-guided elemental combination optimization, and elucidating multiscale synergistic mechanisms, thereby establishing definitive composition-structure-property relationships to direct targeted fabrication of high-performance materials.

Formaldehyde as a volatile organic compound (VOCs) is one of the main indoor gas pollutants produced by building materials, furniture and interior decoration industry. The excessive exposure to formaldehyde can affect human-being health, and lead to nerve damage. Inhaling lower concentrations of formaldehyde can cause cough, allergies, headaches and other symptoms. It is thus of great significance to monitor formaldehyde efficiently, control indoor environmental pollution and maintain human health. In recent years, spinel oxides have some potential application prospects in the field of gas sensing due to their stable crystal structure and good gas sensing performance. CdGa₂O₄ is a kind of wide-band gap semiconductor spinel structure oxide, which has a good gas sensitivity to formaldehyde gas, but it has some problems such as complex preparation process, low yield, high working temperature and low response. Some studies show that metal oxides modified with two-dimensional materials can effectively improve the performance of gas sensors. MXene, represented by Ti₃C₂T_x, is a class of two-dimensional transition metal carbides or carbonitrides, which is widely concerned because of its unique layered structure, large specific surface area, rich functional groups and good electrical conductivity. In this paper, CdGa₂O₄ nanomaterials were prepared by a solvothermal method. On this basis, Ti₃C₂T_x-CdGa₂O₄ composites with different proportions were prepared by a hydrothermal method. The morphology, surface chemical composition and valence state of the elements were investigated, and the gas-sensitive properties of the composite were analyzed.

Ti₃C₂T_x was prepared by using the mixed solution of concentrated hydrochloric acid and LiF (AR, Shanghai Aladdin Reagent Co., China) as an etching agent, and the Al atomic layer in Ti₃AlC₂ was removed by HF generated. CdGa₂O₄ was prepared from Cd (NO₃)₂·4H₂O (AR, Shanghai Sarn Chemical Technology Co., China) and Ga (NO₃)₃·xH₂O (AR, Shanghai Maclin Chemical Technology Co., LTD., China). The Ti₃C₂T_x-CdGa₂O₄ composite was prepared by mixing CdGa₂O₄ with Ti₃C₂T_x magnetically in different proportions, and then reacting at 180 ℃ for 12 h by a hydrothermal method. The phase composition of the materials was analyzed by a model D8 Advance X-ray diffractometer (XRD, Bruker Co., Germany, 40 kV, 40 mA, Cu K_α, λ=0.154 06 nm, 5°-70°) and analyzed by a model JSM-7800F scanning electron microscope (SEM, accelerated voltage 15 kV). The elemental composition of the material was analyzed by a model ESCALAB 250 XI X-ray photoelectron spectrometer (XPS, Thermo Co., USA, accelerated voltage 15 kV), and the specific surface area and pore size distribution of the material were determined by a model ASAP2010C nitrogen adsorption and desorption instrument (Micromeritics Co., USA, accelerated voltage 15kV).

To determine the gas-sensitive properties of Ti₃C₂T_x-CdGa₂O₄ composite material, the sample was ground into a pulp with turpentine permeation alcohol, uniformly coated on the outer wall of alumina ceramic tube. After drying, Ni-Cr heating wire was installed and welded into para-heated components. The working temperature was controlled via adjusting the power added at the both ends of the heating wire and tested after calcination at 170 ℃ for 4 h. The sensitivity was defined as a ratio of the material stability resistances in air and a target gas, and the relative humidity of the test environment was constant (i.e., 50%).

The SEM images show that granular CdGa₂O₄ accumulates on the surface of Ti₃C₂T_x with a layered structure. The EDS spectra show that there are elements Cd, Ga and O in the composites, and the ratio is 1∶2∶5∶7, which may be caused in the presence of Ga₂O₃ components in the composites. According to the adsorption desorption isotherm analysis of XPS and N₂, the functional groups (—O, —OH, —F) in Ti₃C₂T_x provide additional active sites for the adsorption of gas molecules. The addition of Ti₃C₂T_x builds the mesoporous structure, and also increases the specific surface area of the composite, exposing more gas adsorption active sites, thus improving the gas sensitive performance of the sensor. The maximum response value of sample TC-3 to 0.01% formaldehyde at 110 ℃ is 105, which is 9.4 times greater than that of pure CdGa₂O₄. The selectivity and sensitivity of the sensor to different gases at 110 ℃ are investigated. The results show that the sample TC-3 has good selectivity and detection limit for formaldehyde, and the lowest detection limit is 0.00001%, which proves that the prepared sensor TC-3 has a great practical application potential.

In this paper, CdGa₂O₄ nanomaterial was prepared by a solvothermal method, Ti₃C₂T_x with a layered structure was prepared with LiF and concentrated hydrochloric acid system, and then Ti₃C₂T_x-CdGa₂O₄ composite was prepared by a hydrothermal method. The gas sensitive properties of CdGa₂O₄ and a series of Ti₃C₂T_x-CdGa₂O₄ composites were investigated. The results showed that at 110 ℃, the response value of sample TC-3(7% Ti₃C₂T_x-CdGa₂O₄) composite to 0.01% formaldehyde gas was 105, the lowest detection limit was 0.00001%, compared with pure CdGa₂O₄, thus improving the sensitivity and reducing the operating temperature. The combination of appropriate amount of Ti₃C₂T_x could be conducive to improving the gas sensitivity of CdGa₂O₄ material to formaldehyde gas.

Refrigeration technology is widely used in military, commercial, industrial, and civilian fields. However, the existing mechanical compression refrigeration technology faces limitations such as large volume, high energy consumption, low cooling efficiency, and environmental unfriendliness, making it unable to meet the growing demands of emerging technological fields. The electrocaloric effect (ECE), which refers to the alignment of dipoles in polar materials under an electric field, leading to changes in entropy (ΔS) and temperature (ΔT), offers a promising alternative. Solid-state electrocaloric coolers based on the ECE are directly driven by electrical energy, which can achieve heat transfer and cooling. They exhibit some advantages such as high energy efficiency, ease of miniaturization and integration, and environmental friendliness, making them a highly potential and efficient refrigeration technology. Barium titanate (BaTiO₃)-based ceramics have attracted extensive research attention in the electrocaloric field due to their excellent polarization strength and rich phase structures. However, some challenges such as low breakdown electric fields, high sintering temperatures, and the inability to simultaneously optimize working temperature ranges and polarization strength hinder their practical applications. To address these issues, this work was to incorporate sintering additives CuO/Li₂CO₃ into lead-free Ba_0.97Ca_0.03Sn_0.1Ti_0.9O₃ ceramics to promote dense grain growth and optimize the breakdown electric field. The dielectric constant was improved, while maintaining the broad temperature range and continuous phase transition characteristics of BCST ceramics, ultimately achieving a large electrocaloric temperature change of 3.37 K (@55 ℃, 160 kV·cm^-1).

Ba_0.97Ca_0.03Sn_0.1Ti_0.9O₃ powder was synthesized by a conventional solid-state reaction sintering method at 1200 ℃ with BaCO₃, CaCO₃, SnO₂, and TiO₂ as raw materials in a stoichiometric ratio. The ceramic powder was then pressed into disks with the dimensions of φ13 mm×1 mm and sintered at 1350-1500 ℃ for 3 h to obtain dense ceramic samples. After sintering, the ceramic samples were polished, and gold electrodes were sputtered onto their surfaces. The polarization-electric field hysteresis loops (P−E loop) at room temperature were recorded by a model FETS-2000 ferroelectric tester (Wuhan Yanhe Technology Co., Ltd., China) under a frequency of 10 Hz. The values of ΔT were tested through a model RdF P/N 27134-3 heat flux sensor. The dielectric properties were obtained by a model PK-CPT1705 test system (PolyK Technologies Co., USA) with a testing temperature range from 25 to 150 ℃ and a frequency range from 100 Hz to 100 kHz. The microstructure of the grain was determined by a model GeminiSEM 300 scanning electron microscope (SEM) (Zeiss Co., Germany) and a model 7000 S/L X-ray diffractometer (XRD) (Shimadzu Corp., Japan).

The XRD patterns reveal that all ceramic samples exhibit a pure perovskite structure, indicating that Cu²⁺ and Li⁺ ions diffuse into the BCST lattice to form a solid solution. The addition of CuO/Li₂CO₃ causes the XRD diffraction peaks shifting to lower angles, indicating that Li⁺(the radius of 0.73 Å) and Cu²⁺(0.71 Å) substitute the B-site Ti⁴⁺(0.61 Å) and Sn⁴⁺(0.71 Å), leading to a lattice expansion. The SEM images demonstrate that the incorporation of CuO/Li₂CO₃ results in significant grain growth and well-developed, highly dense microstructures in the ceramic samples. The grain size increases from 7 μm to 46 μm due to the low melting points of CuO/Li₂CO₃, which induces liquid-phase sintering effects during the early stages of the sintering process, thus promoting mass transfer and facilitating grain growth and ceramic densification. Dielectric temperature spectra indicate that the addition of CuO/Li₂CO₃ significantly enhances the dielectric constant of BCST ceramics. This improvement can be attributed to two factors, i.e., the increase in grain size; second, the aliovalent acceptor doping of Cu²⁺ and Li⁺ substituting Ti⁴⁺ and Sn⁴⁺, which generates lattice defects and oxygen vacancies . These defects coupled to form dipole clusters, thereby enhancing the dielectric constant. Also, the local random electric fields caused by the charge mismatch between Cu²⁺/Li⁺ and Ti⁴⁺/Sn⁴⁺, as well as the average ionic size effect, due to the reduction in the phase transition temperature. Polarization-electric field (P-E) loops show a significant increase in the polarization strength of the ceramic samples with the addition of CuO/Li₂CO₃, which can also be attributed to the role of dipole clusters. The electrocaloric performance of the material is greatly enhanced, with the BCST-CL ceramic achieving a giant electrocaloric temperature change of ΔT = 3.37 K (i.e., at 55 ℃, E = 160 kV·cm^-1).

The Ba_0.97Ca_0.03Sn_0.1Ti_0.9O₃ (BCST) ceramic samples with varying amounts of CuO/Li₂CO₃ sintering additives exhibited a single perovskite structure, characterized by large, well-developed grains and a dense microstructure. The addition of CuO/Li₂CO₃ sintering agents enhanced the dielectric constant of the material, while preserving the broad continuous phase transition temperature range of BCST. During the sintering process, Cu²⁺ and Li⁺ ions entered the grains, leading to lattice expansion and increased ferroelectric displacement. Also, as acceptor dopants, they formed defect dipole clusters with oxygen vacancies, thereby improving the material's polarization strength. The direct measurement tests demonstrated a significant enhancement in the electrocaloric temperature change (ΔT) of the ceramic samples, while maintaining excellent operational stability. The BCST-CL composition achieved a maximum ΔT of 3.37 K (at 55 ℃, 160 kV·cm^-1), providing a feasible strategy for further improving the performance of electrocaloric ceramic materials.

The generation of biological wastes such as cow dung and aloe vera waste (AVW) causes a serious ecological pollution. The microbial electrolytic cell coupled with anaerobic digestion (MEC-AD) system can make a rational utilization of these biodegradable organic wastes, which is of vital importance for alleviating environmental deterioration and reducing resource waste. Electrode materials and accelerants are the two major factors that affect methane production in the MEC-AD system. They affect microbial attachment and electron transfer in the MEC-AD system. Bio-based carbon materials are carbon materials prepared from biomass as raw materials. They have characteristics such as a rich pore structure, good chemical stability, biocompatibility, and controllable surface properties, which can be used as accelerants and electrodes in the MEC-AD system to optimize its performance. This study was to investigate the influence of biomass-derived carbon as an electrode and accelerant on the performance of the MEC-AD system, and the mechanism for increasing the production of biogas and methane was also analyzed, thus providing a basis for the multifunctional application of biomass-derived carbon in the MEC-AD system.

A series of experimental methods were adopted to study the MEC-AD system. Two types of bio-based carbon, i.e., aloe vera waste derived spherical carbon (AVW-SC) and porous carbon (AVW-PC), were synthesized via hydrothermal carbonization. The raw AVW material was washed with water, dried, ground, and subjected to hydrothermal treatment to obtain AVW-SC. After activating AVW-SC with KOH, it was carbonized in a tube furnace to obtain AVW-PC.

In the preparation of the electrodes, bio-based carbon (AVW-SC and AVW-PC) was mixed with 5% polytetrafluoroethylene powder in ethanol and deionized water, and then ground in a ball mill for 4 h to form a slurry. The slurry was evenly sprayed on the Ti mesh, dried and sintered in N₂ atmosphere at 360 ℃ to obtain Ti-SC and Ti-PC electrodes.

Four groups of experiments were conducted to determine the optimal voltage, compare different carbon electrodes, and explore the optimal coating amount. The MEC-AD reactor adopted 500 mL wide-mouthed glass bottles with a working volume of 400 mL. Each MEC-AD system received a co-substrate mixture of cattle dung and aloe vera waste and inoculum of sewage sludge in a mass ratio of 3∶7. Afterward, they were placed at (36±1) ℃ for 35 d. The biogas was collected by a water displacement method.

The materials were analyzed by characterization techniques such as X-ray diffraction (XRD) and scanning electron microscopy (SEM), and electrochemical tests were conducted on different electrodes. The composition, pH, TS, VS, TCOD and nutrient content of biogas were analyzed by standard chemical methods. Microbial community analysis was conducted using high-throughput sequencing technology. The modified Gompertz model was adopted to predict the kinetic parameters, and the coulombic efficiency and methane recovery rate were calculated according to a specific formula.

The result shows that AVW-SC is spherical and closely aggregated, while AVW-PC has a three-dimensional network structure, with average pore diameter of 9.77 nm. The electron exchange capacity (EEC) of AVW-PC (i.e., 0.75 μmol·e^-/g) is higher than that of AVW-SC (i.e., 0.15 μmol·e^-/g), indicating a better electron exchange capacity. These results indicate that AVW-PC provides more substrate and bacteria accumulation sites, and has better electron-donating and electron-accepting ability, thus improving the digestion efficiency.

In the MEC-AD system, using Ti mesh as an electrode, the effect of different voltages (i.e., 0, 0.4, 0.6, 0.8 V and 1.2 V) on the system performance is investigated, obtaining the optimum biogas production and organic matter degradation rate at 0.8 V. AVW-SC and AVW-PC are respectively coated on Ti mesh as electrodes. The results show that the MEC-AD system with AVW-PC coated Ti mesh as the electrode has a better performance. The electrochemical analysis shows that the electrode coated with AVW-PC has a larger specific capacitance and a smaller charge transfer resistance, indicating that AVW-PC can improve the electrochemical properties and electron transfer ability of MEC-AD system. The influence of coating amount (i.e., 0.025, 0.05, 0.10, 0.15, and 0.20 g) of AVW-PC on the MEC-AD system is investigated. At a coating amount of AVW-PC of 0.1 g, the cumulative biogas production and methane content of the Ti_0.8-PC_0.1 group both reach the maximum values. Different doses of AVW-PC (i.e., 0.10%, 0.15%, 0.20%, and 0.25%) are added as accelerants in Ti_0.8-PC_0.1. At the addition amount of AVW-PC of 0.20%, the Ti_0.8-PC_0.1/PC_0.2 group performs the optimum biogas production (i.e., 633.63 mL/g VS), methane content (i.e., 65.85%), and total nutrient content of biogas residue (i.e., 42.30 g/kg). In Ti_0.8-PC_0.1/PC_0.2, Bacteroidales, Pseudomonadales, Oscillospirales, Methanobacteraceae, Methanospirillaceae, Methanosarcinacea and Methanosaetaceae significantly increase. The increase in microbial diversity promotes interspecific hydrogen transfer (IHT), interspecific acetic transfer (IAT), and direct interspecific electron transfer (DIET), thereby enhancing methanogenic efficiency.

AVW-SC and AVW-PC were utilized as electrodes and accelerants to enhance methane yield in MEC-AD system. The Ti mesh electrode coated with different concentrations of AVW-PC achieved the optimal biogas production at 0.8 V. Specifically, the Ti_0.8-PC_0.1 combination could generate the maximum total amount of biogas and methane proportion. The Ti_0.8-PC_0.1/PC_0.2 combination exhibited the optimum performance (i.e., biogas yield of 633.63 mL/g VS, methane content of 65.85% and total nutritional content of 42.30 g/kg). High abundances of Bacteroidales, Pseudomonadales, Oscillospirales, Methanobacteraceae, Methanospirillaceae, Methanosarcinaceae, and Methanosaetaceae appeared in the Ti_0.8-PC_0.1/PC_0.2 group, compared to other groups. In addition, an increased microbial diversity led to an enhanced methane production through processes like DIET. This research could highlight the potential significance of AVW-PC as both electrode and accelerator for increasing methane production and provide a perspective for improving MEC-AD performance through multiple applications of biomass-derived carbon.

Lithium extraction from salt lake is essential for ensuring lithium resource security in China, but the design of high-performance lithium extraction membranes from salt lake faces significant challenges. Two-dimensional (2D) membranes with oriented nanochannels consist of 2D nanosheets stacked layer by layer. These membranes have nanoscale channel heights that can be precisely controlled at the sub-nanometer level, making them suitable for the selective separation of lithium (Li) and magnesium (Mg) ions. Typically, the Li⁺/Mg²⁺ selectivity of membrane requires surface modification with positive charge due to the inherent charge differences between Li⁺ and Mg²⁺. Interfacial polymerization (IP) is commonly used for the membrane surface modification. However, the excessive IP reactions can result in excess positive charge, reducing the Li⁺ transport efficiency. Therefore, the design and development of 2D selective membranes with optimized IP reactions while maintaining high lithium-ion transport efficiency is of great significance. Layered montmorillonite (MMT) mineral has natural layered structure and it can be easily exfoliated into 2D nanosheets, which are ideal building blocks for the assembly of 2D membranes. In this work, hydrophilic tannic acid (TA) with negative charge is applied to modify the surface of 2D MMT nanosheets, enabling an enhanced Mg²⁺ rejection and suppressed transport resistance of Li⁺ transport. Our results provide a valuable reference for the design and fabrication of novel 2D membranes with high Li⁺/Mg²⁺ selectivity.

The MMT nanosheet suspension was prepared by ultrasonic exfoliation. The suspension mixed with auxiliary membrane-forming agents were scraped coated and dried on a substrate to obtain 2D MMT membranes. For the preparation of TA-modified membranes, TA was added to the MMT nanosheet suspension and coated on substrate using the same protocol. As-prepared membranes were then used for IP reactions. The membranes were first immersed in a PEI solution 45 s. After washing and drying, the membranes were then immersed in a TMC solution for 15 s. As-obtained membranes were dried in an oven for subsequent nanofiltration and characterizations. The morphology and surface roughness of the 2D MMT membranes were characterized by a JSM 7100F scanning electron microscope (SEM) and a Multi Mode 8 atomic force microscope (AFM). The surface chemical analyses was conducted by a K-Alpha X-ray photoelectron spectroscopy (XPS). The alignment and orientation of internal 2D nanochannels of the MMT membrane were analyzed by a D8 ADVANCE X-ray diffractometer (XRD) and Xeuss 2.0 X-ray wide-angle diffractometer (WAXS).

According to the morphological and structural characterizations, the 2D membranes fabricated with bare 2D MMT nanosheets exhibit a well-oriented 2D nanochannel structure. The alignment of TA-modified 2D MMT nanosheets were unaffected during IP reaction, generating a well-preserved membrane structure according to the cross-sectional SEM and WAXS.

With the increasing content of TA, the rejection of Mg²⁺ increased simultaneously and reached up to almost 100% with 1.5% addition of TA. A negative Li⁺ rejection was also achieved correspondingly. However, excess amount of TA resulted in a deterioration of both the rejection of Mg²⁺ and selective transport of Li⁺. In addition to the selectivity, the TA modification significantly promoted the membrane flux up to 22.5 L·m^-2·h^-1, which was 49% higher than that of bare MMT membrane. The TA modified MMT membrane exhibited consistently high Mg²⁺ rejection under various feed conditions and high performance stability during a 120 h long-term operation.

The enhancement in membrane selectivity and flux through TA modification was due to the promoted IP reaction and a narrowed pore size distribution, validated by XPS measurements and molecular weight cut off (MWCO) tests. Furthermore, the role of TA in membrane formation was revealed by AFM and XPS measurements. The TA molecules can connect the adjacent MMT nanosheets via hydrogen bonding between its phenolic hydroxyl groups and the Al-OH on edge surface of MMT. The negative charge on TA provides more anchoring site for the PEI monomers, thereby promoting the IP reaction. Energy barrier calculated by Arrhenius equation further validated that the TA modification can reduce the Li⁺ transport resistance from 20.91 kJ·mol^-1 to 18.38 kJ·mol^-1 in the 2D nanochannels.

In this work, a TA-modification method was applied to enhance the separation performance of a 2D MMT membrane system. The Mg²⁺ rejection of the modified MMT membrane with optimized TA content reached almost 100%, with a corresponding negative Li⁺ rejection of -9%. The membrane flux was 22.5 L·m^-2·h^-1, after TA modification, which was 49% higher than that of bare MMT membrane. Moreover, the TA-modified membranes exhibited consistently high Mg²⁺/Li⁺ selectivity and flux under various feed conditions and excellent stability during long-term operation.

Topographical and surface chemical characterizations revealed the role of TA molecules in forming hydrogen bonding with the hydroxyl groups on edge surface of MMT nanosheets. The enhancement mechanism of membrane selectivity via TA modification was attributed to the additional negative charge from TA. The addition of TA enabled efficient PEI monomers adsorption, which can promote the IP reaction and reduce the average pore size. Conductivity test and energy barrier calculations further validated that the TA modification was able to reduce the transport resistance of Li⁺, thus realizing the enrichment of Li⁺.