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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.

Purposes The situation of post-disaster site of coal mine underground is complex. Aiming at the fact that traditional A* algorithm-based coal mine robot rescue path planning bears path insecurity, low efficiency, and other problems, and by combining with the raster map and the characteristics that the rescue robot can move along any direction, multi-faceted improvement of the traditional A* algorithm is realized. Methods First, the concept of robot size superimposed to obstacles is introduced to ensure the safety of the path. Second, the computational complexity is reduced by optimising the heuristic function to reduce the number of extensions that deviate from the optimal path nodes, and to reduce the redundant nodes and path transitions. Finally, a dynamic adjustment algorithm is used to round the corners of path turns, and the resulting path is smoothed to improve the operability of path. The optimised path with smaller path cost, shorter time consumption, and fewer turns is finally obtained. Based on the improved A* algorithm, the simulation test of rescue robot path planning under different sizes and different obstacle coverages is carried out by using MATLAB. Findings Compared with the traditional A* algorithm, the improved A* algorithm in rugged environment maps reduces the searching nodes by 26.51%, the computation time by 80.42%, the path length by 31.85%, and the number of turns by 44.44%, which improves the search efficiency and smoothness of the path. Conclusions The improved A* algorithm provides a theoretical basis for the rescue work of coal mine robots under complex working conditions.

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).

In view of the problems of low early strength and weak deformation resistance of ordinary cement-based materials, the cement-based materials were modified by nano-silica sol. The nano-silica sol was charasterized by means of electro-hydraulic servo universal testing, X-ray diffraction, and scanning electron microscopy. The fluidity, stone rate, uniaxial compressive strength, elastic modulus, hydration products, and microstructure of cement-based materials with different water-cement ratios were evaluated. The results show that when the content of silica sol is within 0.5% and the water-cement ratio is less than 1.0, the fluidity of cement slurry can be significantly improved, and the maximum increase is 20.24%. The stone formation rate increases with the increase of nano-silica sol admixture, and the silica sol increases the stone formation rate of slurry with water-cement ratio greater than 0.7 significantly, with a maximum increase of 24.49%. When the content of silica sol is 2%, the compressive strength of the stone body increases the most. The effect of increasing the strength gradually weakens. The incorporation of nano-silica sol promotes the early hydration reaction of cementitious, and reacts with the hydration products to produce hydrated calcium silicate gel (C—S—H) and makes the microscopic morphology more dense, so that the early compressive strength and elastic modulus of the stone body are significantly increased. Nano-silica sol promotes the hydration reaction by shortening the induction period and providing nucleation sites for C—S—H in the particle voids, which improves the performance of cementitious materials.

Abstract Hierarchical Bi2Fe4O9/BiOI S-scheme nanoflower heterostructures are prepared by hydrothermal method, which exhibit exceptional photo-piezoelectric catalytic performance. The tight binding between the sheets ensures the efficient electron transport, and provides a large interface area and adequate reaction sites for photo-piezoelectric catalytic reactions. At the same time, because the water flow in the water body produces hydraulic shear force on the material, the material produces piezoelectric effect. Bi2Fe4O9/BiOI exhibit a remarkable degradation efficiency of 99.4% for tetracycline and a hydrogen production rate of 4089.36 µmol h−1 g−1. The observed behavior can be explained by the combined influence of the formation of S-scheme structure and the process of photo-piezoelectric catalysis, confirmed by in-situ XPS, transient/steady-state fluorescence and piezoelectric response force test. The excellent stability of the material suggests its possible use in the sectors of energy and environment. This work introduces novel concepts for the future advancement of photo-piezoelectric synergistic catalysis.

Photocatalysis is an effective way to solve the problems of environmental pollution and energy shortage. Numerous photocatalysts have been developed and various strategies have been proposed to improve the photocatalytic performance. Among them, Bi-based photocatalysts have become one of the most popular research topics due to their suitable band gaps, unique layered structures, and physicochemical properties. In this review, Bi-based photocatalysts (BiOX, BiVO4, Bi2S3, Bi2MoO6, and other Bi-based photocatalysts) have been summarized in the field of photocatalysis, including their applications of the removal of organic pollutants, hydrogen production, oxygen production etc. The preparation strategies on how to improve the photocatalytic performance and the possible photocatalytic mechanism are also summarized, which could supply new insights for fabricating high-efficient Bi-based photocatalysts. Finally, we summarize the current challenges and make a reasonable outlook on the future development direction of Bi-based photocatalysts.

3D flower-like hierarchical mesoporous Bi4O5I2/MoS2 Z-scheme layered heterojunction photocatalyst was fabricated by oil bath and hydrothermal methods. The heterojunction with narrow band gap of ∼1.95 eV extended the photoresponse to near-infrared region, which showed obvious photothermal effect due to the introduction of MoS2 with broad spectrum response. MoS2 nanosheets were anchored onto the surface of flower-like hierarchical mesoporous Bi4O5I2 nanosheets, thereby forming efficient layered heterojunctions, the solar-driven photocatalytic efficiency in degradation of highly toxic dichlorophenol and reduction of hexavalent chromium was improved to 98.5% and 99.2%, which was ∼4 and 7 times higher than that of the pristine Bi4O5I2, respectively. In addition, the photocatalytic hydrogen production rate reached 496.78 μmol h−1 g−1, which was ∼6 times higher than that of the pristine Bi4O5I2. The excellent photocatalytic performance can be ascribed to the promoted photothermal effect, as well as, the formation of compact Z-scheme layered heterojunctions. The 3D flower-like hierarchical mesoporous structure provided adequate surface active-sites, which was conducive to the mass transfer. Moreover, the high stability of the prepared photocatalyst further promoted its potential practical application. This strategy also provides new insights for fabricating layered Z-scheme heterojunctions photocatalysts with highly photothermal-photocatalytic efficiency.

The g-C3N4/BiOI/CdS double Z-scheme heterojunction photocatalyst with I3−/I− redox pairs is prepared using simple calcination, solvothermal, and solution chemical deposition methods. The photocatalyst comprised mesoporous, thin g-C3N4 nanosheets loaded on flower-like microspheres of BiOI with CdS quantum dots. The g-C3N4/BiOI/CdS double Z-scheme heterojunction has abundant active sites and in situ redox I3−/I− mediators and shows quantum size effects, which are all conducive to enhancing the separation of photoinduced charges and increasing the photocatalytic degradation efficiency for bisphenol A, a model pollutant. Specifically, the heterojunction photocatalyst achieves a photocatalytic degradation efficiency for bisphenol A of 98.62% in 120 min and photocatalytic hydrogen production of 863.44 μmol h−1g−1 on exposure to visible light. The excellent visible-light photocatalytic performance is as a result of the Z-scheme heterojunction, which extends absorption to the visible light region, as well as the I3−/I− pairs, which accelerate photoinduced charge carrier transfer and separation, thus dramatically boosting the photocatalytic performance. In addition, the key role of the charge transfer across the indirect Z-scheme heterojunction has been elucidated and the transfer mechanism is confirmed based on the detection of intermediate I3− ions. Thus, this study provides guidelines for the design of indirect Z-scheme heterojunction photocatalysts.

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.

Ti3+ self-doped rutile/anatase/TiO2(B) mixed-crystal tri-phase heterojunctions photocatalysts are fabricated via hydrothermal approach and mechanochemical process, followed by in-situ solid-state chemical reduction approach. The as-prepared samples are characterized by X-ray diffraction, Raman, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and UV–vis diffuse reflectance spectroscopy. The photocatalysts are consisted by anatase/rutile TiO2 nanoparticles and 1D TiO2(B) single-crystalline nanorods, which form rutile/anatase/TiO2(B) tri-phase heterojunctions. The visible-light-driven photocatalytic degradation rates of methyl orange and phenol are up to ∼98 and 97%, which are 2.2 and 1.8 times higher than that of commercial Degussa P25, 2.3 and 2.2 times higher than that of pure TiO2(B) as well. The enhancement can be attributed to the synergistic effect of special nanostructure, tri-phase heterojunctions, oxygen vacancy and Ti3+ self-doping, which facilitates the absorption of visible light and the spatial separation of photo-generated charge carriers. This work provides a new perspective for designing high-active visible-light-driven photocatalyst in future. Keywords: TiO2, Visible-light-driven photocatalysis, Tri-phase heterojunction, Ti3+ self-doped, Pollutants degradation

Nitrogen doped titanium dioxide (N-TiO2) nano-photocatalysts were successfully synthesized in the presence of ammonium chloride. The resulting materials were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and ultraviolet–visible diffuse reflection spectroscopy (UV–vis DRS). The results of XRD, SEM and TEM revealed that the as-synthesized photocatalyst was composed of spheroidal particles, which were smaller than undoped ones. XPS analysis revealed that N was effectively incorporated into the lattice of TiO2 through substituting oxygen atoms, and N might coexist in the form of substitutional N (O–Ti–N) and interstitial N (Ti–O–N). DRS exhibited that the light absorption edge red-shifted to visible region. The enhanced visible light photocatalytic activity for the degradation of RhB was mainly attributed to the smaller crystal size, more surface hydroxyl groups, stronger light absorption in visible region and narrower band gap energy.

Anatase mesoporous titanium dioxide codoped with nitrogen and chlorine (N-Cl-TiO2) photocatalysts were synthesized through simple one-step sol-gel reactions in the presence of ammonium chloride. The resulting materials were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), and ultraviolet-visible diffuse reflection spectrum (UV-vis DRS). XRD results indicated that codoping with nitrogen and chlorine could effectively retard the phase transformation of TiO2 from anatase to rutile and the growth of the crystallite sizes. XPS revealed that nitrogen and chlorine elements were incorporated into the lattice of TiO2 through substituting the lattice oxygen atoms. DRS exhibited that the light absorption of N-Cl-TiO2 in visible region was greatly improved. As a result, the band gap of TiO2 was reduced to 2.12 eV. The photocatalytic activity of the as-synthesized TiO2 was evaluated for the degradation of RhB and phenol under visible light irradiation. It was found that N-Cl-TiO2 catalyst exhibited higher visible light photocatalytic activity than that of P25 TiO2 and N-TiO2, which was attributed to the small crystallite size, intense light absorption in visible region, and narrow band gap.

Fe-N-S-tri-doped TiO2 photocatalysts were synthesized by one step in the presence of ammonium ferrous sulfate. The resulting materials were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and ultraviolet-visible diffuse reflection spectrum (UV-Vis DRS). XPS analysis indicated that Fe (III) and S6+ were incorporated into the lattice of TiO2 through substituting titanium atoms, and N might coexist in the forms of substitutional N (O-Ti-N) and interstitial N (Ti-O-N) in tridoped TiO2. XRD results showed that tri-doping with Fe, N, and S elements could effectively retard the phase transformation of TiO2 from anatase to rutile and growth of crystallite size. DRS results revealed that the light absorbance edge of TiO2 in visible region was greatly improved by tri-doping with Fe, N, and S elements. Further, the photocatalytic activity of the as-synthesized samples was evaluated by the degradation of phenol under visible light irradiation. It was found that Fe-N-S-tri-doped TiO2 catalyst exhibited higher visible light photocatalytic activity than that of pure TiO2 and P25 TiO2, which was mainly attributed to the small crystallite size, intense light absorbance in visible region, and narrow bandgap energy.