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To address the problem that traditional cement-based slurry materials cannot meet the actual demand for grouting and reinforcement of large deformation roadways in coal mines, some high-performance composite slurry materials are obtained by modifying ordinary Portland cement with nano-silica sol, ethylene-vinyl acetate copolymer (EVA) and fly ash. The orthogonal test and extreme difference analysis are used to systematically study the variation of the physical and mechanical properties of the composite slurries, determine the optimal ratio, and further analyze the difference in the physical properties between the optimal ratio of composite slurries and pure cement, construct the hydration reaction mechanism model of the composite slurries, and elucidate the mechanical properties of the composite slurries for reinforcing broken rocks. The results of the study show that the optimum proportion of composite slurry is 0.7 water-cement ratio, 15% fly ash, 2% silica sol and 7.5% EVA. Compared with pure cement, the rheology of composite slurry is slightly decreased, but the stability and mechanical properties of the slurry are significantly improved, with the initial setting time shortened by 38.9%, the final setting time shortened by 53.8%, the precipitation rate reduced by 60%, the stone rate increased by 3.3%, the uniaxial compressive strength increased by 39.1%, the tensile strength increased by 97.2%, and the tensile/compression ratio increased by 41.7%. Silica sol and fly ash undergo volcanic ash reaction with Ca(OH)2 to generate more calcium silicate hydrate (C-S-H) and calcium aluminate hydrate (C-A-H) at different times, which promotes the hydration reaction of the composite slurry and accelerates the film formation of EVA to make the stone body more dense. The injection volume of the composite grout and the uniaxial compressive strength of the bonded body both increase with the increasing grouting pressure. With the increase in the Talbot index, the compressive strength first increases and then decreases. The failure mode is often characterized by bulging, and shear dilation deformation is pronounced. When the grouting pressure exceeds 2 MPa and the Talbot index is 0.5, the bond strength of the grout is higher, and the damage is reduced. This study provides a feasible way for early strength and toughening modification of ce-mentitious composite pastes.

Electrokinetic remediation technology can effectively remove heavy metal ions from contaminated soil in coal mine area. In order to clarify the effect of electric field on the adsorption characteristics of heavy metal ions on the surface of kaolinite, three common heavy metal elements Pb(II), Cd(II) and Cu(II) in mine soil were studied, a three-dimensional visualization model was established, and a stable kaolinite-solution-kaolinite simulation system was optimized. Molecular dynamics simulation method was used. The adsorption mode, atomic density distribution, diffusion coefficient and radial distribution function of heavy metal ions on kaolinite (001) crystal plane under electric field were investigated. The results show that when the electric field direction is +Z, the electric field promotes the complexation between heavy metal ions and siloxane surface, and the coordination number of the first hydration shell of heavy metal ions decreases with the increase of electric field intensity. The adsorption percentage of outer complexes increases with the increase of electric field intensity. When the electric field direction is −Z, the adsorption percentage of the outer complex decreases with the increase of the electric field intensity, the interaction between the kaolinite surface and heavy metal ions weakens, and more heavy metal ions dissociate in the solution and pair with chloride ions; under the action of electric field polarization, there is no obvious boundary between the first and second hydration shells of heavy metal ions, and there is water molecular exchange between the hydration shells; under the action of electric field, the MSD curve of heavy metal ions on kaolinite shows anisotropy. The diffusion coefficient in X and Y direction is larger than that in Z direction, the total diffusion coefficient increases with the increase of electric field intensity, and the diffusion coefficient is not obviously affected by the positive and negative direction of electric field. Pb(II) ion and Cd(II) ion only have outer complexes on the surface of kaolinite, while Cu(II) ions have the adsorption mode of coexistence of inner and outer complexes. The adsorption priority of kaolinite to three heavy metal ions is Pb(II) > Cu(II) > Cd(II).

The development of high-efficient photocatalysts plays an important role in the sustainable utilization of solar energy. Hollow nanostructured photocatalysts are vital for solar light utilization and charge carrier separation in photocatalytic processes. Therefore, the construction of hollow semiconductor photocatalysts is a promising strategy for preparing novel high-efficient photocatalysts. This paper reviews common hollow semiconductor nanomaterials, such as oxides, sulfides, nitrides, C3N4, MOFs, and their composite photocatalysts. The characteristics of hollow-structure photocatalysts, the application of solar energy conversion, and their understanding of the photocatalytic mechanism are also reviewed. In addition, future challenges will be focused on designing and majorizing broadband response hollow-structure photocatalysts to further enhance solar energy conversion. Hollow semiconductor photocatalysts will have potential applications in the natural environment, and these synthesized strategies can also provide new possibilities for synthesizing other high-performance semiconductor photocatalysts.