State Key Laboratory of Coal Mine Disaster Dynamics and Control

Strength and deformation behaviors of rockfill materials, key factors for determining the stability of dams, pertain strongly to the grain crushing characteristics. In this study, single-particle crushing tests were carried out on rockfill materials with nominal particle diameters of 2.5 mm, 5 mm and 10 mm to investigate the particle size effect on the single-particle strength and the relationship between the characteristic stress and probability of non-failure. Test data were found to be described by the Weibull distribution with the Weibull modulus of 3.24. Assemblies with uniform nominal grains were then subjected to one-dimensional compression tests at eight levels of vertical stress with a maximum of 100 MPa. The yield stress in one-dimensional compression tests increased with decreasing the particle size, which could be estimated from the single-particle crushing tests. The void ratio-vertical stress curve could be predicted by an exponential function. The particle size distribution curve increased obviously with applied stresses less than 16 MPa and gradually reached the ultimate fractal grading. The relative breakage index became constant with stress up to 64 MPa and was obtained from the ultimate grading at the fractal dimension (α=2.7). A hyperbolical function was also found useful for describing the relationship between the relative breakage index and input work during one-dimensional compression tests.

Abstract Environmental pollution and energy crisis have become major challenges to sustainable development of human society. Solar‐driven photocatalytic technology is regarded as an extremely attractive solution to environmental remediation and energy conversion. Unfortunately, practical applications of traditional photocatalysts are restricted owing to the poor absorption of visible light, insufficient charge separation and undefined reaction mechanism. Therefore, developing novel visible light photocatalysts and exploring their modification strategies are significant in the area of photocatalysis. Bi‐based photocatalysts have attracted wide attention due to unique geometric structures, tunable electronic structure and decent photocatalytic activity under visible light. At present, Bi‐based photocatalysts can be mainly classified as bismuth metal, binary oxides, bismuth oxyhalogen, multicomponent oxides and binary sulfides, and so forth. Although they can be used as independent photocatalysts for environmental purification and energy development, their efficiency is not ideal. Therefore, many efforts have been made to enhance their photocatalytic performance in the past few decades. Significant progresses in determining the fundamental properties of photocatalysts, improving the photocatalytic performance and understanding the photocatalytic mechanism in important reactions have been made benefited from the various new developed concepts and approaches. This review introduces the structural properties of Bi‐based photocatalysts in detail and summarizes the design and modification strategy for improving the photocatalytic performance, including metal/nonmetal doping, construction of heterojunctions, regulation of crystal facet exposure, and structural defects. Furthermore, we discuss the catalysis mechanisms of Bi‐based materials in terms of semiconductor photocatalysis and plasmonic photocatalysis. Finally, the applications, challenges and prospects of Bi‐based photocatalysts are proposed to guide the future work. image

Microbially induced calcium carbonate precipitation (MICP) has attracted great attention recently for its ability to improve the mechanical properties of soils. Calcium carbonate (CaCO3) precipitates that formed at the contact points and on the surface of particles or in the pore space of soil matrixes could increase the bonding strength, friction, and interlocking resistances due to the enhancement of the interparticle bonds, particle roughness, and packing density, and therefore, greatly improve the macroscopic performances of biocemented soils that were subjected to external loading. Strength is one of the key factors when determining the application of biotreatments in geotechnical engineering during the construction and operation periods. This study presented a systematic, objective, and extensive review of the strength of biocemented soils that was based on previous research. The improvement characteristics were comprehensively investigated under compression, tension, and static and cyclic shear conditions, for unconfined compressive (UCS), splitting tensile (STS), yielding, shear, and cyclic resistance strengths. Particle scale regimes were elaborated to interpret the improvement mechanism in the biotreatment and failure modes in biocemented specimens under external loading. Furthermore, the challenges of biocementation were discussed, and future investigations were envisioned.

A bibliometric analysis of published papers with the key words "positive matrix factorization" and "source apportionment" in 'Web of Science', reveals that more than 1000 papers are associated with this research and that approximately 50% of these were produced in Asia. As a receptor-based model, positive matrix factorization (PMF) has been widely used for source apportionment of various environmental pollutants, such as persistent organic pollutants (POPs), heavy metals, volatile organic compounds (VOCs) as well as inorganic cations and anions in the last decade. In this review, based on the papers mainly from 2008 to 2018 that focused on source apportionment of pollutants in different environmental media, we provide a comparison and summary of the source categories of typical environmental pollutants, with a special focus on polycyclic aromatic hydrocarbons (PAHs), apportioned using PMF. Based on the statistical average, coal combustion and vehicular emission, are shown to be the two most common sources of PAHs, and contribute much more to emissions than other sources, such as biomass burning, biogenic sources and waste incineration. Heavy metals were mainly from agricultural activities, industrial and vehicular emissions and mining activities. Quantitative source apportionment on pollutants such as VOCs and particulate matter were also apportioned, showing a prominent contribution from fossil-fuel combustion. We conclude that, aside from natural sources, abatement strategies should be focused on changes in energy structure and industrial activities, especially in China. Source apportionment of typical POPs including polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs), polychlorinated biphenyls (PCBs), halogenated flame retardants (HFRs) and perfluorinated compounds (PFCs) is less comprehensive and further study is required.

A significant pressing issue in microbially induced calcium carbonate precipitation (MICP) is the characterization of the heterogeneous growth mechanics of calcium carbonate (CaCO3) crystals. This study aimed to visualize the bacteria and CaCO3 distributions at the quiescent state through microfluidic chip tests where the bacterial solution (BS) and cementation solution (CS) were initially injected simultaneously from two separate microchannels and subsequently converged in a reaction microchannel. The experiments revealed that the bacterial diffusion within the CS injection area was hindered for a high concentration of calcium chloride (CaCl2) (e.g., 0.5 M), whereas diffusion appeared homogeneous for a low concentration of CaCl2 (0.05 M). In addition, the CaCO3 distribution along the width of the reaction microchannel was more uniform for 0.05 M CaCl2 than for 0.5 M CaCl2. The microfluidic chip tests in this study provided kinetic observations of the MICP process that improved the understanding of the mechanics of bacterial diffusion and CaCO3 crystal growth and their variation with different concentrations of CaCl2.

The selective crystal facet growth of BiOX (X = Cl, Br, I) is very significant since each facet possesses different physicochemical properties.

Rational design of the crystal structures of electrode materials is considered as an important strategy to construct high-performance supercapacitors.

Oxide-derived Cu (OD-Cu) exhibits unique and excellent C2 product selectivity (ethanol, ethylene, etc.) in the field of electrocatalytic reduction reaction of CO2 (eCO2RR), which has a great application value in realizing effective storage of renewable energy and the artificial closed carbon cycle. However, the Cu2O structure encounters complex structure evolution under negative potential conditions, making it difficult to obtain the specific active structures. Here, we found an operando activation strategy for the OD-Cu catalyst based on the cyclic voltammetry (CV) process conducted in CO2-saturated solution. Assisted by an interval eCO2RR, the sluggish octahedral–Cu2O (o-Cu2O) evolves into active Cu/Cu2O–CV, with the formed "metallic Cu" uniformly anchoring on o-Cu2O and accompanied by rich Cuδ+–Cu0 grain boundaries. Combined with in situ and ex situ characterization, compared to o-Cu2O, Cu/Cu2O–CV significantly promoted the formation of C2 products (FEC2 increased from 17.13 to 73.44%). By enhancing the adsorption of CO* and subsequently the formation of O*C*COH intermediates, the Faraday efficiency for ethanol was significantly improved from 5.15% (on o-Cu2O) to 56.56% (on Cu/Cu2O–CV). Our study provides evidence for a previously unexplored function of CO2 in the evolution of o-Cu2O catalysts into highly active structures for the generation of multicarbon products, opening a pathway for the rational design of future catalysts for the electrochemical reduction of CO2.

This paper presents the results of a study on the evolution of particle shape in carbonate sands that underwent different degrees of particle breakage. Carbonate sand specimens with three different initial particle sizes were subjected to impact loadings with different input energies. The particle sizes and shapes of the tested sands were analyzed by dynamic image analysis both before and after each loading. An increase in the input energy resulted in increases in particle breakage, aspect ratio, sphericity, and roundness to steady-state values, whereas convexity was barely influenced in the tests. It was found that the Weibull distribution could be used to describe the cumulative distributions of the particle-shape parameters. A relative shape-variation index for quantitatively describing the change in particle shape was correlated with the relative breakage index, which quantitatively describes the extent of particle breakage. Based on microscopic images of the particles at different loading states, the dominant particle-breakage mode gradually transited from the initial fracture mode to the attrition and abrasion mode with an increase in input energy, leading to the production of much more rounded and spherical particles.

The stress–strain curves for shale specimens under different fluids saturation.

O) gel structure observed by XRD, FTIR and SEM can physically encapsulate the contaminants during geopolymerization. It is finally concluded that heavy metals were immobilized in the fly ash based geopolymer through a combination of chemical bonding and physical encapsulation.

Degradation of geomaterials, that is, particle breakage, can be harmful to the full life-cycle stability of practical engineering; for example, rockfill dam, energy-pile foundation, railway embankment, and retaining wall. A key issue is how to precisely quantify grain crushing during the life-cycle operation of the project that suffers high pressure or dynamic loading. This paper reviews the advantages and limitations of existing particle breakage indices and proposes a new simple breakage index for estimating the evolution of grain crushing. The new index without an integral grading area can be easily and directly obtained from the sieving results and independent of the coordinate of particle size axis. It can also adequately capture the grain crushing at all grain sizes. Moreover, it can be used for uniformly graded, well-graded, and gap-graded crushable soils.

With regard to using the electric energy generated by renewable sources, the CO₂ electroreduction reaction (CO₂RR) for the production of fuels is helpful for creating an artificial carbon cycle.

MnOx-decorated MgAl layered double oxide (M-LDO) was fabricated via merging of memory effect and anion intercalation, accompanied by the reduction/calcination process. The as-obtained nanocomposites were characterized by scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), powder X-ray diffraction (XRD) and N2 adsorption-desorption. To clarify the detailed formation mechanism, optimized calcination temperature/time and temperature for methyl orange (MO) adsorption were investigated. Adsorption experiments showed that the adsorption behaviour fitted well with a Langmuir isotherm and pseudo-second-order model, and the maximum adsorption capacity calculated from the Langmuir model was 555.55 mg g(-1). The adsorption process was exothermic and spontaneous in nature. Moreover, the used adsorbent could be regenerated for at least five cycles (94% removal retained) through a thermal procedure, indicating that the M-LDO hybrid is a promising adsorbent with promising ability to remove anionic dye pollutants from wastewater.

A new numerical method, which is called the General Particle Dynamics (GPD) method, is proposed to investigate the zonal disintegration mechanism of isotropic rock masses around a deep circular tunnel subjected to dynamic unloading as well as the stress distributions. A constitutive model based on the GPD method is developed to simulate the zonal disintegration phenomenon in deep rock masses. The number and size of fractured and nonfractured zones are determined using the nonlinear unified strength criterion. It is shown from the numerical results that the dynamic loads and high in situ stress are two dominant factors for the occurrence of zonal disintegration.

This paper includes an investigation of the thermal conductivity of biocemented soils to better understanding the regimes of heat transmission through soils treated by microbially induced calcium carbonate precipitation (MICP). A series of thermal conductivity tests using the transient plane source method (TPS) was performed on biocemented silica sand specimens with different gradations, void ratios, and MICP treatment cycles. The results showed that MICP treatment greatly improved the thermal conductivity of sand specimens. An increase in uniformity coefficient or a decrease in void ratio of the sand resulted in an increase in the thermal conductivity of MICP-treated specimens for a given MICP treatment cycle. The increment of thermal conductivity of MICP-treated specimens with respect to that of untreated specimens was also affected by gradation, void ratio, and content of calcium carbonate. The greatest improvements in thermal conductivity were achieved for sands having an initial degree of saturation between 0.82 and 0.85. An empirical equation was established to predict the thermal conductivity of MICP-treated silica sand with different variables, which may be useful in designing energy piles in biocemented sand layers.

Halide perovskites are potential humidity-detection materials due to their sensitivity to water, but the instability of traditional lead-based halide perovskites and the toxicity of Pb hinder further application in humidity sensing. Here, lead-free Cs3Cu2Br5 perovskite microcrystals passivated by surface ligands (OLA and OAm) are used to prepare an environmentally friendly humidity sensor. The humidity sensing performance of the prepared sensors was tested, and the effect of surface ligands of perovskites on the performance of humidity sensors was analyzed. The results show that the impedance variations of the manufactured humidity sensors at 12 to 95% relative humidity are 106Ω (OLA) and 105Ω (OAm), respectively. Besides, the sensors demonstrated excellent repeatability, low hysteresis, and considerable stability at different RH values. Furthermore, the analysis of the different ligands attests that short-chain OLA is more conducive to the formation of porous films with stronger water absorption capacity, further improving the responsiveness of the sensor. By contrast, and long-chain OAm is more conducive to the formation of dense films, improving the response ability at low humidity. Additionally, the more hydrophilic OLA contributes to greater responsiveness, while the more hydrophobic OAm helps to shorten the response and recovery time.

Benefiting from the electromagnetic enhancement of noble metal nanoparticles (NPs) and the capture ability of organic frameworks, plasmonic metal–organic framework (MOF) structures have greatly promoted the development of gas detection by surface-enhanced Raman spectroscopy (SERS). In those detections, the kinetic process of gaseous molecules in plasmonic-MOF structures has a great influence on SERS spectra, which is still lacking intensive investigation in previous reports. In this work, the kinetic processes of gaseous thiophenol compounds (TPC) in the plasmonic Zeolitic Imidazolate Framework (Ag@ZIF) core–shell NPs are studied by SERS spectra. The experimental data demonstrate that the SERS intensities of gaseous TPC could be enhanced once more in an H2 mixed gas environment with different functional groups of TPC. Further results reveal that the two-step enhancement of SERS intensities is not only related to the thicknesses of the MOF shell but also affected by the ambient mixed gas. To understand this novel phenomenon, the binding energy between the gaseous molecule and ZIF is calculated based on first-principles computation. In combination with the plasmonic properties of the Ag core, a molecular collision model is introduced here to show the distribution of gaseous TPC molecules in ZIF, which could be responsible for this interesting two-step enhancement of SERS intensities. Furthermore, the H2 assisted kinetic process of gaseous p-aminothiophenol (PATP) is also analyzed by the classical pseudo-first-order kinetic model, which is consistent with our experimental SERS data. Our work not only reveals the novel phenomenon of plasmonic-MOF structures to improve the gas detection by SERS spectra but also enriches the understanding of the microcosmic process of gaseous molecules in the mixed gas environment to optimize MOF structures for gas capture and storage.

Depleted oil fields in the Gulf of Suez (Egypt) can serve as geothermal reservoirs for power generation using a CO2-Plume Geothermal (CPG) system, while geologically sequestering CO2. This entails the injection of a substantial amount of CO2 into the highly permeable brine-saturated Nubian Sandstone. Numerical models of two-phase flow processes are indispensable for predicting the CO2-plume migration at a representative geological scale. Such models require reliable constitutive relationships, including relative permeability and capillary pressure curves. In this study, quasi-static pore-network modelling has been used to simulate the equilibrium positions of fluid–fluid interfaces, and thus determine the capillary pressure and relative permeability curves. Three-dimensional images with a voxel size of 0.65 μm3 of a Nubian Sandstone rock sample have been obtained using Synchrotron Radiation X-ray Tomographic Microscopy. From the images, topological properties of pores/throats were constructed. Using a pore-network model, we performed a sequential primary drainage, main imbibition cycle of quasi-static invasion in order to quantify (1) the CO2 and brine relative permeability curves, (2) the effect of initial wetting-phase saturation (i.e. the saturation at the point of reversal from drainage to imbibition) on the residual-trapping potential, and (3) study the relative permeability-saturation hysteresis. The results improve our understanding of the potential magnitude of capillary trapping in Nubian Sandstone, essential for future field-scale simulations.

Electro-kinetic remediation of Cr-contaminated soil by three-dimensional electrode coupled with a permeable reactive barrier.