Tensile softening (σ-w) curve is a critical parameter necessary to model the non-linear fracture behavior of concrete structures by the finite element method. The uniaxial tensile test is the most direct approach to determine the softening curve, but it is a challenge due to its insufficient stiffness of the loading machine, eccentricity, asymmetric fracture modes, and multiple cracking. Alternatively, a softening curve can be derived via minimizing the deviation between the predicted and experimental results based on the load-crack mouth open displacement (F-l_CMOD) curve measured by the bending or wedge-splitting tests. Inverse analysis methods are commonly used to derive σ-w curve include the J-integral, poly-linear, and global optimization. Although the J-integral method is computationally least demanding, it requires conducting the tests on two specimens with different notch sizes for deriving each σ-w curve, yielding a lower precision and a higher dispersion. For the given test data, the poly-linear method can produce a unique solution without any pre-assumptions regarding the softening curve's shape. However, it is sensitive to arbitrarily small measurement errors, yielding a softening curve with severe oscillation, and accumulating all previous errors in the current analysis step. The global optimization technique is not easy to converge when there are many fitting variables, and it needs to pre-assume the shape of the softening curve. There is no guarantee that the outputs of this technique will be globally optimal. Therefore, this paper proposed a self-modifying inverse analysis method to determine the softening curve of concrete after combining global best-fitting with an automatic correction technique.

The self-modifying inverse analysis method belongs to the global optimization technique with more additional constraints. This method consists of two modules, i.e., global best fitting and parameter self-modifying. The former mainly focuses on the optimum fitting of the F-l_CMOD curve to minimize the cumulative deviation between the simulated and measured values. For this purpose, a computational program was developed a software named MATLAB. In this program, the ability to define search boundaries for each control variable increases the robustness of the fitting algorithm and lessens the likelihood of finding a pseudo-optimal solution. Despite, the optimal solution may be still the local minimum in some situations, so it is also necessary to check whether the local error requirement is satisfied at each discrete point and to find out the maximum load deviation as the second criterion for evaluating the prediction accuracy. Thus, the role of the second module is to automatically modify the optimal value of the fitting parameter when the second criterion is not met. After providing the corrected parameter values (including the boundaries) to the first module, the global optimization procedure is executed again until the load tolerance error is satisfied. The current model cannot accurately simulate the crack propagation process if the load condition cannot be satisfied after the maximum number of iterations. It is required to add a new line segment to the current softening model and conduct the global fitting procedure again with the model containing additional variables until the load criterion is satisfied or the maximum number of line segments is reached. In this algorithm, it is possible to output a precise global optimal solution even when the initial estimate of fitting parameters differs from the ideal solution or the initial softening model is relatively simple.

For the sample, in all regions of the F-l_CMOD curve, the simulated responses match well with the experimental results, and the maximum relative error between the calculated and measured loads is less than 5%. This indicates that the developed method can accurately simulate the crack propagation process of concrete, and this method is highly versatile, applying to different specimen forms and various concrete materials. The fracture energy determined by the F-l_CMOD curve is in a reasonable agreement with that by the σ-w curve, and their deviation does not exceed 2%, further confirming the rationality of the recommended technique. Concrete exposed at different humidities exhibits a similar shape to the softening curve, consisting of a fast descending, a slow descending, and a tail. The tensile strength (f_t) increases with decreasing age while critical crack width (w_c), finally tending to their stabilizing values. For a given age, f_t and w_c decrease with reducing ambient humidity, and this decrease is more significant in the later stages, which is due to the lack of sufficient water in the pores for hydration reaction, the non-uniform shrinkage deformation between aggregate and mortar, and the disturbance of local structure of C-S-H.

Although there are multiple "optimal" solutions at different initial fitting parameters, the ideal σ-w curve is rather narrow, implying that the algorithm converges to the similar solutions. The determined softening curve is independent of the initial estimate, and the algorithm is robust. In the case of different initial models, the optimal σ-w curve is similar with only some minor differences in the tails. This demonstrates that the softening model's initial form has little effect on the optimization outputs, and trustworthy optimal solutions can be obtained even by a simple beginning model.

The self-modifying inverse analysis method could consider the effect of local response on the softening curve, allow the definition of searching boundaries of the fitting parameters, and eliminate the need to predefine the final shape of the softening curve, reducing the probability of obtaining a "pseudo-optimal solution" and weakening the dependence of the optimization output on the initial guesses. In all the region of the F-l_CMOD curve, the calculated load was correlated well with the experimental result, and the fracture energy determined by the F-l_CMOD curve differed by no more than 2% one by the σ-w curve. The proposed method was highly robust and versatile. It could accurately determine the σ-w curve of various concrete materials with different specimen configurations, and the resultant optimal solution was independent of the initial estimate of fitting parameters and the initial shape of the softening model. Concrete exposed at different humidities exhibits a similar shape to the softening curve. The f_t increased with decreasing age while critical crack width w_c, finally tending to their stabilizing values. f_t and w_c decreased as the ambient humidity decreased, and this reduction was more pronounced in the later age.

Although different experiments on the co-corrosion of concrete vulcanization and carbonation are performed, the data are scattered and are not systematic. There are little reports on the mechanism of the performance degradation of cement-based materials due to the coupled effects of high temperature, high humidity, SO₂ and CO₂. It is thus of a great theoretical and practical significance to scientifically evaluate the durability of industrial building concrete structures and investigate the durability damage mechanism and performance degradation of industrial building concrete structures.

In this paper, the neutralization process of cement-based materials under the coupling action of high temperature, high humidity, SO₂ and CO₂ was investigated with the three levels of cement paste, mortar and concrete. The appearance, neutralization depth, and quality change rules of cement-based materials with different water-cement ratios were analyzed. The porosity and pore solution of cement-based materials were determined by nuclear magnetic resonance (NMR) and electrochemical impedance (EIS). In addition, the neutralization mechanism of cement-based materials was discussed, and a prediction model for the neutralization depth of cement-based materials was also established.

The cement used was P.O 42.5. The fine aggregate was a natural river sand with a fineness modulus of 2.34, and the coarse aggregate was a granite crushed stone with a continuous gradation of 5-25 mm. Three types of samples were cement paste, mortar, and concrete. In the test, a prism-shaped sample of 100 mm×100 mm×400 mm was used to test the neutralization depth of the sample, and a cubic sample of 100 mm×100 mm×100 mm was used for quality and microscopic tests, with 3 samples in each group. The tests began after 28 d of standard curing of the samples.

A concentration ratio of CO₂ and SO₂ in the workshop was approximately 20∶1, and the temperature and humidity were at 50 ℃ and 70%, respectively. The rapid carbonation test method based on the Chinese National Standard GB/T50082—2009 was used. The ambient temperature of the vulcanization test box was 50 ℃, the relative humidity was 70%, and the SO₂ concentration was 0.9% (the maximum concentration of SO₂ in this test box was 0.9% due to the limit of the SO₂ sensor). For the carbonization box, the ambient temperature was 50 ℃, the relative humidity was 70%, and the CO₂ concentration was 20%. The samples were covered with epoxy, leaving only two sides. The sample was placed on a bracket in the vulcanization box, and the distance between each sample was not less than 50 mm. The sample was vulcanized for 1 d and carbonized for 1 d as one cycle. The samples were tested when the cycles reached 0, 2, 4, 7 and 14. The appearance, quality and neutralization depth of cement-based materials were examined. The pore characteristics and pore solution changes in the samples before and after corrosion cycles were analyzed by NMR and EIS.

Based on the analysis of cement slurry, mortar, and concrete samples, the neutral depth of cement pure pulp is the largest, and the neutral depth after 14 cycles is approximately 35 mm. The neutral depth of the mortar sample after 14 cycles is approximately 13 mm. The overall neutralization depth of the concrete is the smallest, and the difference is not large. The neutral depths after 14 cycles are 6.42, 6.95 mm and 8.19 mm, respectively. The depth of the neutral depth of the ingredients on the cement base is obvious. The aggregate can reduce gas transmission in the sample. The maximum neutral depth of mortar and concrete is decreased by 59.85% and 77.52%, respectively, compared with cement paste.

The pore rate for paste is increased by approximately 3%. For mortar, the pores increase slowly. After 7 cycles, the pore rate is increased rapidly by approximately 8%. For concrete, the pores decrease first and then increase slowly by approximately 1%. For different materials under the common action of carbonization and vulcanization, the pore rate of cement base materials is generally increased.

The initial proportion of harmful pores in concrete is larger than that in paste and mortar. However, the increase in harmful pores in mortar and cement paste is significantly larger than that in concrete as corrosion cycle increases. The harmful pores of concrete increase slowly, and the harmful pores decrease significantly after the 14th cycle. Concrete harmful pores are increased by approximately 0.4%. The harmful pores of the mortar are increased by approximately 0.8%. The harmful pores of the cement paste are increased by approximately 0.6%.

In the early stage of the corrosion cycle, the concentration of CO₂ was relatively high, and the reaction was mainly carbonization. In the middle of the corrosion cycle, CaCO₃ filled in the pores of the sample so that the reaction slowed down and the mass increased slowly. SO₂ could react with calcium-containing substances, resulting in expansion cracks. SO₂ could also lead to decalcification of CSH, further increasing the porosity and accelerating the transmission of gas inside the sample. In the later stage, the carbonization reaction speed accelerated, and the sample mass began to increase again. The neutralization depth of different samples changed approximately in the same manner, i.e., firstly increasing rapidly and then increasing slowly as the number of corrosion cycle increases. The porosity changes in the sample at all levels were similar, and the less harmful pores gradually increased and decreased after 14 cycles. For harmful holes and more harmful holes, the cement paste and mortar samples increased gradually, while the concrete samples firstly increased and then decreased after 14 cycles.

The superior performance of foam concrete has promising applications in the fields of building energy saving, roadbed and mine filling. Although the effects of foaming agents and foam stabilizers on the bubble performance are investigated, the bubble performance by different matrix materials and slurries still needs to be further improved, achieving a synergistic enhancement of matrix and bubbles. The large-volume utilization of solid waste matrix materials in foam concrete is a key to realizing the promotion of foam concrete considering the wide range and low price of solid waste materials. The durability of foam concrete still needs to be systematically discussed. In addition, it is also necessary to conduct in-depth exploration of the green multi-purpose application of foam concrete to provide theoretical and experimental supports for the high-quality development of building materials.

Using as supplementary cementitious materials (SCM) is one of the most important research topics in the resource utilization field of steel slag. However, the iron oxide content in steel slag is greater than that of other cementitious materials (i.e., clinker, granulated blast furnace slag, and fly ash). The solid solution formed by FeO and CaO-MnO-MgO (RO phase), hematite, wustite, Ca₂Fe₂O₅(C₂F) and other Fe-bearing phases have little contribution to the activity of ground steel slag. Some researchers use reductants such as H₂, CO, anthracite, silicon carbide, and carbon powder to reduce iron oxides from molten steel slag into ferroalloys. Aluminosilicate melt is quenched and resultant residual used as SCM. These methods have a challenge of high cost of reducing agents and difficulty in industrial utilization. This paper used residual carbon in coal gangue as a reductant to reduce iron oxides of steel slag. The remaining aluminosilicate was quenched to prepare slag with a high hydration activity, which could achieve the synergistic disposal of two types of industrial solid waste.

Based on the chemical composition of steel slag and coal gangue, as well as the fixed carbon content of coal gangue, the amount of coal gangue required for the sufficient reduction of iron oxide in the two raw materials was determined. After mixing ground coal gangue and ground steel slag thoroughly, the mixture was heated to 1 200, 1 300, 1 350, 1 400, 1 450 ℃ and 1 500 ℃ at 40 ℃/min in an argon atmosphere (3 L/min), and then quenched with water after holding for 30 min. The resultant strip off iron particles, and the remaining aluminum silicate is called water quenched residue (WQR). The iron recovery rate was determined according to the chemical composition of the WQR. The mineral phases were determined by an X-ray diffractometer (XRD, Rigaku Co., Japan), and the glass content in water quenched residue was calculated using the Rietveld quantitative analysis method.

The paste and mortar samples were prepared by adding 30% (in mass fraction) WQR into the reference cement. The cross-sectional morphology was determined by a model GeminiSEM 500 scanning electron microscope (Zeiss Co., Germany). The elements distribution of the paste samples was analyzed. The heat release curve of hydration for the first 72 h was recorded with a model TAM-Air-8microcalorimeter (TA Instruments Co., USA). The thermal behavior of the pure slurry after hydration for 3 d, 7 d and 28 d were analyzed by a model TGA/DSC1/1600 thermogravimeter (TG, Mettler Toledo Co., USA). The mortar specimens with a dimension of 40 mm×40 mm×160 mm were used for testing flexural and compressive strength after standard curing to the specific age.

The reduction temperature is an important factor affecting the iron recovery rate in steel slag and the vitrification of WQR. When the reduction temperature exceeds 1 300 ℃, the reduction rate significantly increases. When the temperature exceeds 1 350 ℃, the Fe₂O₃ content decreases from 20% in the steel slag raw material to less than 2% in the WQR. The main mineral phases in the reduced residue at 1 100 ℃ are merwinite and gehlenite. When the temperature rises to 1 350 ℃, the diffraction peaks of gehlenite disappear. At 1 450 ℃, the diffraction peaks of merwinite almost disappear. When the reduction temperature is less than 1 300 ℃, the glass content in WQR is less than 60%. When the temperature reaches 1 350 ℃, the glass increases rapidly, approaching 80%. The glass exceeds 90% with further increasing the reduction temperature to 1 450 ℃. The fusion temperature is an important factor for the degree of vitrification of WQR.

The hydration heat release curve of cement paste shows that the second exothermic peak of sample prepared with WQR generated at 1 500 ℃ is similar to the peak of the reference cement, but the exothermic peak attributed to the formation of the second ettringite decreases. The second exothermic peak of cement with WQR at 1 400 ℃ is 1 mw/g lower than that of WQR cement at 1 500 ℃. A lower heat release rate is due to the presence of crystalline phases in the WQR at 1 400 ℃. After 72-h hydration, a higher cumulative heat of the paste prepared with WQR at a higher melting temperature occurs. The cumulative heat of WQR cement at 1 400 ℃ and 1 500 ℃ is 71.65% and 85.64% of the reference cement, respectively. This is due to the high reduction temperature leading to a high degree of vitrification, thereby improving the hydration activity of the WQR.

The XRD and TG results indicate that the Ca(OH)₂ content in the paste gradually decreases with the increase of steel slag reduction temperature and the hydration time of WQR cement. This is because the glass content and pozzolanic activity of WQR increase with the increase of reduction temperature. Consequently, the Ca(OH)₂ content of WQR cement decreases.

The strength results of the mortar show that the 3-d flexural strength of cement with 30% WQR is almost equivalent to that of the reference cement. The growth rate of flexural strength of WQR cement is higher than that of reference cement with curing time, and its strength reaches 130% of reference cement strength at 28 d. The compressive strength of WQR cement at 3 d is 60% of the reference cement. The compressive strength development rate of WQR cement is higher than that of reference cement. After 28-d hydration, the compressive strength of cement prepared with WQR at 1 400 ℃ reaches 90% of the reference cement strength.

The recovery rate of Fe could reach 63%~94% by using carbon in coal gangue as a reducing agent to reduce iron oxide of steel slag. The reduction rate increased as the reduction temperature increased. When the reduction temperature was below 1 300 ℃, the mineral phases of the WQR mainly consisted of merwinite and gehlenite. The crystalline phase gradually decreased as the temperature increased. When the reduction temperature was >1 450 ℃, the glass content maintained at 91%. The glass phase content and the pozzolanic activity in WQR increased as the reduction temperature increased. The cement prepared with WQR had good mechanical properties. After 28-d hydration, the flexural strength and compressive strength of WQR cement reached 130% and 90% of the reference cement, respectively.

Graphene is a novel two-dimensional carbon material composed of sp and sp² hybrid carbon atom topologies. This material has attracted widespread attention in various fields such as materials, chemistry, physics, information, biology, and the environment due to its high conjugation, abundant acetylene bonds, regular ordered pores, and adjustable electronic structure, which still has many challenges and opportunities in the future.

1) Developing large-scale, high-quality, and low-cost synthesis technology can provide a solid material foundation for theoretical research and practical applications. The preparation methods for other types of graphene (such as GY, GY-3, and GY-4) are still in the exploratory stage. Obtaining novel graphene materials will expand the application field and clarify the structure-activity relationship.

2) The alkyne bonds of graphene provide more designability. Designing chemical reactions based on alkyne bonds is of great significance for improving the performance of non-metallic catalytic materials. Synthesizing graphene and its derivatives with precise structures, controlling the degree of reaction and functionalization of alkyne bonds can effectively expand the scope and depth of "alkyne chemistry".

3) A more precise manipulation of the pore structure of graphene is needed. The precise regulation from molecular pores to nanopores will deepen the understanding of the atoms/ions transport and anchoring in GDY, and fully leverage its structural advantages. Accurately controlling the anchoring points, atomic numbers, and atomic types of metal elements is crucial for developing atomic catalytic materials, enhancing catalytic activity, selectivity and stability.

The unique rich alkyne bond and pore structure of graphene provide infinite possibilities for the precise synthesis and controllable preparation. This review can provide a reference to understand the development of graphene materials for various applications.

Carbon dioxide emissions generated during the production of cement-based materials are one of the important sources of global greenhouse gas emissions. Various technological innovations and improvement measures are introduced to reduce carbon emissions in cement industry. Among these, CO₂ can be fixed in concrete to form a stable calcium carbonate by solidifying CO₂ or accelerating carbonization, thereby reducing the release of CO₂ into the atmosphere. This carbonization process can effectively reduce the carbon dioxide produced by concrete and improve the comprehensive performance of concrete to a certain extent. However, the carbonization process is complicated due to the diverse components of concrete materials. The existing studies indicate that the components such as calcium silicate hydrate, ettringite, and calcium hydroxide in the concrete can participate in the carbonization reaction, and different components have different effects on the formation process of calcium carbonate. Therefore, this paper investigated the nucleation and growth process of calcium carbonate in confined space of different components by a molecular dynamics simulation method to reveal the formation mechanism of calcium carbonate in confined space. In addition, the structural characteristics of each component in concrete and the mechanism of their interaction with carbon dioxide were also analyzed.

The adsorption models of calcium carbonate in C-S-H, AFt, CH and SiO₂ confined space were established, respectively, to investigate the cluster formation process at the interface between calcium carbonate and different components of concrete. For C-S-H, the model includes C-S-H matrix and aqueous solution containing calcium carbonate. The C-S-H substrate with a Ca/Si ratio of 1.7 was used as a substrate model, and the supercell was cut along the crystal plane parallel to (001) to form the surface of the C-S-H substrate. The overall model size is 43.20 Å×45.04 Å×80.00 Å, and the pore size of the substrate is 4 nm. A total of 60 CO₃^2-, 60 Ca²⁺ and 2 000 water molecules were randomly placed in the pores, and the ion concentration in the solution was 1.4 mol/L. The other three matrices have the same size as the C-S-H matrix, and the concentration of Ca²⁺ and CO₃^2- in the pores is the same as that of the above C-S-H system. Also, four matrix models with confined space of 3 nm and 5 nm were established, respectively, to explore the influence of pore size on calcium carbonate. Before the formal simulation, the conjugate gradient method was used to minimize the energy, and then the isothermal isobaric ensemble (NPT) was used in the simulation process. The temperature was set to 300 K, the running time was 10 ns, and the time step was set to 1 fs. The clay force field (ClayFF) was used to simulate the C-S-H, AFt, CH, and SiO₂ matrix, respectively, and the carbonate solution used a separate force field parameter. The application of the mixed force field to different components in the model could more accurately simulate the dynamic characteristics and interactions between the components.

In the case of bonding and local structure, the C-S-H, AFt and CH matrix form a stable and strong bonding structure between the interface region and the ions in the solution. Especially in the C-S-H system, Ca_c and CO₃^2- in the pores form more bonds with the ions at the interface of the matrix and have a stronger interaction. In contrast, the adsorption capacity of the ions in the pores is obviously weak, and only a small amount of ions are adsorbed due to the lack of calcium ions on the surface of the SiO₂ matrix.

The nucleation mechanism of calcium carbonate clusters is more consistent with the pre-nucleation theory. The whole simulation process can be divided into three stages, i.e., rapid agglomeration, cluster growth and cluster densification. The stronger interaction between the ions at the interface of the C-S-H matrix and the free ions in the solution lead to the aggregation of calcium carbonate clusters at the interface, providing more nucleation sites for the further nucleation and growth of calcium carbonate. Therefore, calcium carbonate has the optimum nucleation and agglomeration effect in the C-S-H matrix. Also, the pore size of the confined space has a great influence on the formation process of calcium carbonate. When the pore size is 3 nm, the surface of the C-S-H, CH and AFt matrix has a stronger attraction to the free ions in the solution, which is conducive to promoting the rapid nucleation and growth of calcium carbonate. When the pore size increases to 5 nm, the nucleation and growth process of calcium carbonate clusters slows down due to the weakened effect of the matrix interface on the ions in the solution.

The ions at the interface of the matrix had a great influence on the formation of calcium carbonate clusters. For different components of concrete, calcium carbonate and matrix surface ions attracted each other to form ionic bonds, which were then adsorbed at the interface for nucleation and growth. It was easier to bond with carbonate and calcium ions in the pores because C-S-H had more free hydroxyl groups and calcium ions at the interface, providing more nucleation sites for the agglomeration and growth of calcium carbonate at the interface. Also, the attraction of the substrate surface to the free ions in the solution was stronger when the pore size was 3 nm promoting the nucleation and growth of calcium carbonate. The nucleation mechanism of calcium carbonate clusters in the matrix pores did not follow the classical nucleation theory, but calcium ions and carbonate ions combined in the form of ionic bonds to form smaller clusters and then aggregated to grow and nucleate. In this process, it was unnecessary to overcome a large nucleation energy barrier, which was consistent with the pre-nucleation mechanism.

It is necessary to explore efficient and environmentally friendly energy storage devices due to the rapid consumption of fossil fuels and increasing environmental pollution. Among various energy storage devices, supercapacitors have some advantages of high power density, short charging and discharging time, good cycle stability, safety and reliability. The related studies focused on transition metal oxides and sulfides. However, their conductivity and cycle stability are rather poor. Compared with transition metal oxides and sulfides, transition metal selenides as an advanced multifunctional material dominate the field of energy storage and conversion by virtue of their high theoretical capacity, good electrical conductivity, and good cycling stability. Also, the coexistence of different metal cations with multiple valence leaps enables multiple redox reactions and enriches structural defects, and the coupling between the bimetals favors the regulation of the electronic structure and improved electrical conductivity, resulting in better electrochemical activity than monometallic selenides. Transition metal selenide electrodes for electrochemical studies are usually prepared with polymer binders by conventional slurry coating methods, which increases the dead volume of the active transition metal selenide surface and decreases the contact with the electrolyte. Therefore, transition metal selenides can be designed and prepared on a conductive substrate with an ideal porous network to obtain better charge storage performance. In this paper, NiMo precursor was firstly synthesized on a nickel foam substrate by a hydrothermal method, and then NiSe/Mo₁₅Se₁₉ electrode materials were prepared via in-situ selenation reaction of this precursor with Se powder. In addition, the effect of NiMo ratio on their electrochemical properties was also investigated.

A 2 cm × 4 cm nickel foam (NF) substrate was firstly pretreated with 2 mol/L HCl, acetone, anhydrous ethanol and deionized water, and then 6 mmol of Ni(NO₃)₂-6H₂O and 3 mmol of Na₂MoO₄-2H₂O were dissolved in 60 mL of deionized water. The dissolved mixture and 1 block of pre-treated NF were added into a PTFE-lined reactor, and the hydrothermal reaction was carried out at 150 ℃ for 5 h. The effect of nickel and molybdenum molar ratio (i.e., 1∶1 and 3∶1) on the electrochemical performance was investigated. Finally, the precursor and 0.13 g of Se powder were placed at the two ends of a quartz boat into a tube furnace in Ar gas as a protective gas at 350 ℃ for 2 h. After natural cooling, NiSe/Mo₁₅Se₁₉ was obtained. The crystal structure of the samples was determined by a model D8AA25 X-ray diffractometer (XRD, Bruker). The microstructure of the samples was observed using a model S-4800 scanning electron microscope (SEM, Hitachi Co., Japan). The morphology, lattice, and lattice spacing of the samples were analyzed by a model F30G2 transmission electron microscope (TEM, Tecnai). The molecular structure, elemental valence states and chemical bonding were analyzed by a model Xi+ X-ray photoelectron spectroscope (XPS, ESCALAB). The electrochemical properties of the samples in the three-electrode system and the two-electrode system were tested by a model CHI660E electrochemical workstation (Chenhua Co., China) under an electrolyte of 6 mol/L KOH. Three-electrode measurements were carried out using Pt as a counter electrode and saturated calomel as a reference electrode. The ASC devices were made with NiSe/Mo₁₅Se₁₉ as a positive electrode and activated carbon (AC) as a negative electrode in the two-electrode system.

The SEM images show that the Ni∶Mo molar ratio has an effect on the morphology of the samples. When the Ni∶Mo molar ratio is 1∶1, the sample morphology is the coexistence of flower-like microspheres composed of nanorods and nanosheets, and the disorganized molecular pore arrangement is not conducive to the flow of electrolyte ions. The diameter of the microspheres composed of nanosheets is approximately 1 μm, the thicknesses of the nanosheets are 30-40 nm, the diameters of the nanorods are 150-200 nm, and the length of the nanorods is approximately 2 μm. When the Ni∶Mo molar ratio is 2∶1, the morphology of the sample is nanorods, and they are grown vertically oriented on the NF substrate, with the lengths of the nanorods of 1.0-1.5 μm, and the diameters of the nanorods of 50-120 nm. At the Ni∶ Mo molar ratio of 3∶1, the morphology of the sample is flower-like microspheres composed of nanosheets, the diameters of the microspheres are 1.5-2.0 μm, and the thicknesses of the nanosheets are 20-30 nm. The electrochemical test shows that the sample has the optimum electrochemical performance when the molar ratio of Ni∶Mo is 2∶1. The specific capacitance of the sample is 940.9 F/g at the current density of 1 A/g, and the specific capacitance of the sample is 940.9 F/g when the current density increases from 1 A/g to 10 A/g. The electrode with n(Ni)∶ n(Mo) of 2∶1 still maintains a specific capacitance of 75.5% when the current density increases from 1 A/g to 10 A/g. This is since the rod-like nanostructure possesses a large specific surface area, thus providing more active sites for the electrochemical reaction and being beneficial to the energy storage device. From the TEM images, NiSe/Mo₁₅Se₁₉ nanorods have a porous structure due to the release of gases during the calcination process. This unique porous structure can provide more transport channels for electrolyte ions and a large number of active sites in the Faraday reaction.

NiSe/Mo₁₅Se₁₉ composites had an optimum electrochemical performance at a Ni∶Mo molar ratio of 2∶1. The sample-specific capacitance was 940.9 F·g^-1 at a current density of 1 A·g^-1. In addition, this electrode material exhibited good multiplication properties and cycling stability. The NiSe/Mo₁₅Se₁₉//AC hybrid supercapacitor (ASC) made from NiSe/Mo₁₅Se₁₉ and activated carbon (AC) had a high energy (i.e., 46.5 Wh·kg^-1) and a power density (i.e., 800 W·kg^-1), indicating that NiSe/Mo₁₅Se₁₉ composites have a promising application potential in energy storage devices.

Graphite carbon nitride (g-C₃N₄) composite manganese cobalt based prussian blue (MnCoPBA/g-C₃N₄) catalyst was prepared by a self-assembly method, a coprecipitation method and a high-temperature annealing method. The catalyst prepared was used to analyze the catalytic degradation of rhodamine B (RhB) in the SR Photo Fenton like system. The MnCoPBA/g-C₃N₄ catalyst has a degradation efficiency of 96% for RhB within 10 minutes and exhibits a good cyclic stability. The catalyst also has a good catalytic degradation performance for RhB at pH values of 1-9, indicating a superior applicability in acidic, neutral, and weakly alkaline environments.

Catalytic performance test is an important indicator for evaluating MnCoPBA/g-C₃N₄ catalysts. A certain amount of MnCoPBA/g-C₃N₄ (0.05-0.20 g/L) catalyst was added into 100 mL of RhB (5-20 mg/L) solution. The suspension was stirred magnetically for 30 min to achieve adsorption-desorption equilibrium. Subsequently, 3 mL of suspension was taken and centrifuged to add the supernatant to a colorimetric dish. The data were recorded using a UV spectrophotometer. Subsequently, in a xenon lamp (350 W, >420 nm), a certain amount of PMS (5-60 mg/L) was added and 3 mL of suspension was treated by centrifugal force every 5 minutes to obtain the supernatant. The data were recorded in a UV spectrophotometer until the solution become colorless and the UV absorption spectrum data unchanged.

The cyclic stability of catalysts is an important indicator for evaluating their practical application. To reduce the possible experimental errors caused by catalyst loss in the cyclic experiment, the cyclic experiment was designed as a parallel experiment, where each cyclic experiment was conducted independently. Sampling was no longer conducted during the n-1st cycle before the n-th cycle experiment, and sampling was conducted again during the n-th cycle experiment. The experimental operation was the same as the catalytic experiment. The waste liquid was collected and centrifuged, and the product was washed and dried with deionized water and ethanol. The UV spectrophotometer was used to test the data and collect records.

Based on the analysis of the results, a possible catalytic degradation mechanism for the Photo-Fenton like system was proposed. The photocatalytic excitation of g-C₃N₄ semiconductor material in the Photo-Fenton like system generates photo- generated electrons and hole pairs, which are captured by metal ions in MnCoPBA and undergo a reduction reaction, achieving an effective separation of photo-generated carriers in the photocatalytic system and overcoming the defect of high photo-generated carrier recombination efficiency in g-C₃N₄ photocatalytic system. Simultaneously achieving a closed loop cycle of Fe(Ⅲ)/Fe(Ⅱ), Mn(Ⅲ)/Mn(Ⅱ) and Co(Ⅲ)/Co(Ⅱ) ions in the Fenton like system is obtained. An energy support for the Fenton like system is provided. The rate limiting step is broken through, and the defect of ion deficiency in the Fenton like system is overcome. Also, photo-generated electrons can directly activate PMS to generate SO₄^·-, triggering chain reactions to produce ·OH, and reacting with O² to form ·O₂^-. Various strong oxidizing radicals efficiently degrade RhB, thus improving the catalytic degradation performance.

MnCoPBA/g-C₃N₄ catalyst was prepared by a coprecipitation method combined with a high-temperature calcination method. The effect of catalytic condition on the catalytic degradation performance of RhB was investigated. The results indicated that when MnCoPBA/g-C₃N₄-2.5 had the optimal catalytic degradation efficiency for RhB under the optimum condition (i.e., the catalyst dosage of 0.1 g/L, RhB concentration of 10 mg/L, PMS dosage of 0.15 g/L, and pH values of 1-9). The catalytic degradation mechanism indicated that Mn and Co metal ions in MnCoPBA acted as mediators for photocatalytic and the Fenton like connections, capturing photo-generated electrons to slow down the rate of photo generated electron hole recombination. Also, the reduced metal ions could promote the Fenton like reaction to decompose PMS, producing the more intense oxidizing free radicals and accelerating the catalytic degradation of RhB. The catalytic degradation efficiency of RhB was 90% within 2 min, and 96% within 10 min. In addition, the catalyst also exhibited a good cycling stability.

Ga₂O₃ is an ultra-wide bandgap semiconductor, which has a direct bandgap of 4.9 eV. Also, it has the superior thermodynamic and chemical stability, making it suitable for the development of deep ultraviolet optoelectronic devices. Ga₂O₃ exhibits the superior photosensitive and resistive properties, which has a promising application in sensor-memory integrated optoelectronic devices. In this paper, the crystal structure, composition, and morphology of the Ga₂O₃ thin film grown via pulsed laser deposition (PLD) was discussed, and then an optoelectronic device with Pt/Ga₂O₃/NSTO/In structure was designed and constructed. The physical mechanism of the Ga₂O₃-based device was investigated. The device process was optimized to achieve both high sensitivity ultraviolet photo-response and stable resistive switching characteristics. This work can provide theoretical guidance and technical support for the development of novel Ga₂O₃-based multifunctional optoelectronic devices.

Ga₂O₃ thin films were grown on (100) Nd∶ SrTiO₃ (NSTO) substrates by the PLD method. The target material used was a pure Ga₂O₃ ceramic target prepared by a solid-state method. Before thin film deposition, the ceramic target was pre-ablated for 3 min to remove surface contaminants. The film deposition was performed at pulse laser energy of 300 mJ, O₂ partial pressure of 3.0 Pa, and substrate temperature of 650 ℃. The target rotation speed was 5 r/min, the substrate rotation speed was 10 r/min, the pulse laser frequency was 5 Hz, and the deposition time was 30 min. Based on the deposited Ga₂O₃ thin films, a device with metal/Ga₂O₃/electrode sandwich structure was further constructed. At room temperature, Pt metal dot electrodes were fabricated on the surface of Ga₂O₃ thin films by a DC magnetron sputtering method as a top electrode of the device, and then weld the metal indium (In) directly onto the back of the NSTO substrate as a bottom contact electrode. The above Pt metal electrode preparation process was run at DC source power of 100 W, working pressure of 1.5 Pa, Ar flow rate of 10 mL/min, substrate rotation of 10 r/min, and sputtering time of 60 s.

The structure of Ga₂O₃ thin films was characterized by a model D8 Discover type high-resolution four circle single crystal X-ray diffractometer. The elemental composition of Ga₂O₃ thin film material was analyzed by a model Escalab 250Xi X-ray photoelectron spectroscope. The surface and cross-sectional morphology of the films was characterized by a model Sigma 500 field emission scanning electron microscope. A semiconductor electrical performance testing system was constructed by a model Keithley 2635 digital source meter, probe station, and electromagnetic shielding dark box, to examine the I-V scanning loop, multi-level resistive state, retention, and fatigue resistance characteristics of the device. A 255 nm LED light source was driven by a digital signal generator to test the time-dependent UV photoresponse characteristics. A Omni-λ 3027 setup consisting of monochromator, 150 W xenon lamp light source, chopper, collimating light converter, and phase-locked amplifier, was utilized to measure the dark current, spectral response, UV-visible suppression ratio, and detectivity of the photodetector.

The deposited β-Ga₂O₃ film with small particles and a flat and dense surface exhibits (004) plane preferential orientation. The Pt/Ga₂O₃/NSTO/In device with both fast self-driven ultraviolet photoresponse and stable resistive switching characteristics was fabricated. Under illumination, the photocurrent of the device rapidly increases to its maximum value and then gradually decreases to a steady state possibly due to the reduction in the Schottky junction built-in electric field caused by the injection of photogenerated carriers into the barrier region. The self-driven photoresponse is attributed to the efficient separation of photo-generated carriers by a built-in electric field formed at the Pt/Ga₂O₃ interface. On the other side, the device exhibits a stable bipolar resistive switching behavior. Alternating -5 V and +3 V pulse voltages with a 10 ms pulse width results in a resistive switching ratio of nearly 10⁴. A rapid switching between multi-level resistance states occurs at different pulse voltages. The intrinsic oxygen vacancy defect in Ga₂O₃ thin film as the trap center dominates the capture/release process of charge carriers, thereby maintaining the resistance state. Changing the pulse voltage can control the amount of electron injection, thus affecting the height of the interface barrier, which can explain the multi-level resistive characteristics of the device. The resistance state shows a good retention, and there is no significant degradation within 10⁴ s, showing the nonvolatile characteristics. In addition, the device also exhibits stable and fast switching characteristics after multiple repeats, indicating potential applications in memory devices. The mechanism of resistive switching effect can be attributed to the interface type resistance mechanism. The variation of the Schottky barrier caused by external electrical injection and the carrier trapping/detrapping process caused by the oxygen vacancy defect trap center jointly determine the resistive switching effect.

The fabricated device had a fast UV photoresponse (τ_r/τ_d=60 ms/120 ms) with a peak responsivity of 13.4 mA/W and 1.49×10¹¹ Jones (λ=250 nm) at 0 V bias. According to the analysis, the Schottky contact formed at the Pt/Ga₂O₃ interface resulted in a fast self-driven photoresponse at 0 V bias. In addition, the fabricated device also exhibited a stable bipolar resistive switching behavior with a high/low resistance ratio of 10⁴. The fast switching between multiple resistance state was achieved with the superior anti-fatigue and retention characteristics at different pulse voltages. The external electric field and oxygen-vacancy trap centers was considered as the main origin of resistive switching effect in Ga₂O₃-based optoelectronic device.

Photocatalytic oxidation degradation of cyanide is an effective technology to treat cyanide wastewater. TiO₂/SiO₂ is a common catalyst. A preliminary research indicates that the pore structure of SiO₂ has a certain influence on the degradation of cyanide and the removal of zinc and copper. If TiO₂ particles are only loaded on the surface of mesoporous SiO₂, the contact between the surface of SiO₂ and the target substance in wastewater is reduced, thus affecting its adsorption performance. In this study, a macroporous SiO₂ was prepared, and TiO₂ particles were loaded on the surface and in three-dimensional interconnected channels of SiO₂, thus increasing the adsorption sites on the surface of SiO₂ and improving the adsorption performance of target pollutants, and enhancing its efficiency of treating cyanide in wastewater.

Gravity self-assembled polystyrene microspheres (PS) were used as hard templates, impregnated in silica sol for 8.0 h, dried in an oven at 60 ℃, and roasted in a Muffle furnace at 550 ℃ for 10 h to obtain macroporous SiO₂. SiO₂/TiO₂ precursors were prepared by a sol-gel method and roasted at 500 ℃ for 90 min. SiO₂/TiO₂ composites with a three-dimensional interconnected macroporous structure were prepared. The wastewater and materials were placed and mixed in a beaker in a certain proportion. After stirring magnetically for a period of time, a small air pump was used to pump air into the bottom of the beaker at room temperature, and a high-pressure mercury lamp was used as the light source for photocatalytic oxidation of the wastewater. The effects of TiO₂ particle loading mass, catalyst dosage, catalytic time, adsorption time on the treatment of cyanide wastewater were investigated. N₂ adsorption-desorption, scanning electron microscopy (SEM), X-ray diffraction spectroscopy (XRD), Fourier transform infrared spectroscopy (FTIR) and other characterization techniques were used to determine the structural characteristics of the material and its adsorption-catalytic degradation mechanism.

PS presents a monodisperse, independent and spherical structure with a particle size of 1.65 μm. PS templates are arranged in an orderly manner, independent of each other but closely connected, and they do not show a large continuous structure. SiO₂ is a three-dimensional ordered macroporous structure with a pore size of 1.2 μm, which is smaller than the diameter of microspheres, indicating that the skeleton structure shrinks during the roasting process. SiO₂ particle is broken mainly because of mechanical grinding. The long distance of the channels is orderly, the large holes are uniform and interconnected through small holes. The sizes of the small holes are 170-220 nm, the holes are formed due to the accumulation of microspheres. TiO₂ particles are fragmented and loaded on the concave surface of SiO₂. The particle size of TiO₂ is uneven, and smaller than the pore size of SiO₂. TiO₂ particles are evenly dispersed on the surface of SiO₂ or in the physical structure of the cavity, which eliminates the agglomeration of TiO₂. N₂ adsorption-desorption test shows that the SiO₂/TiO₂ material has a large pore structure, and the specific surface area is increased by 5 times, compared with TiO₂ nanoparticles. The thermogravimetric curve shows that the materials have less weight loss at 250-800 ℃. The X-ray diffraction pattern of the material shows that the diffraction peak intensity of SiO₂ loading with TiO₂ particles decreases. The experimental results show that the degradation efficiency of total cyanide and the removal efficiencies of copper, iron and zinc are 98.79%, 99.10%, 100.00% and 92.26%, respectively, under the optimum conditions (i.e., 10% of TiO₂ particle loading mass, 0.35 g of the material mass when treating 100 mL cyanide wastewater, 1.0 h of dark adsorption and 4.0 h of illumination time). The material was regenerated in a sulfuric acid solution by ultrasonic treatment. Under the same experimental conditions, the total cyanide degradation efficiency is reduced by 4.95% after three catalytic cycles, indicating that the material has strong stability and reusability. The XRD results before and after adsorption-catalysis show that ZnO, CuSCN, Cu₂Fe(CN)₆ and Fe₂O₃ are adsorbed on the surface of the material. The FTIR results show that a characteristic peak of C≡N appears on the surface of the material after 1-h adsorption and a characteristic peak of NO₃^- appears after 4-h catalysis. The EDS of the material after 1-h adsorption shows that cyanide is adsorbed on the surface of the material, and metal ions are uniformly distributed on the surface of the material. The EDS of the material after 4-h illumination shows that the metal content is higher than that after 1-h adsorption, and the distribution of Si and Ti is uniformly crossed. The results of free radical quenching experiment show that electron capture by oxygen is the main factor to improve the catalytic effect.

Macroporous SiO₂/TiO₂ materials were prepared by PS self-assembly template, impregnation, roasting and loading, which were used to treat cyanide wastewater. Under optimal experimental conditions, the degradation efficiency of total cyanide and the removal efficiencies of copper, iron and zinc were 98.79%, 99.10%, 100.00% and 92.26%, respectively. The three-dimensional ordered pore structure of macroporous SiO₂ made TiO₂ particles evenly dispersing on its surface and inside the cross-linked pore. The mechanism indicated that the cyanide was degraded into non-toxic nitrogen oxides and carbon oxides, and the metals were removed by precipitation.