The influence of the type of N dopping on the performance of bifunctional N-doped ordered mesoporous carbon electrocatalysts in oxygen reduction and evolution reaction

To develop more ideal bifunctional heteroatom-doped carbon electrocatalysts toward the oxygen reduction reaction(ORR) and oxygen evolution reaction(OER) for regenerative fuel cells and rechargeable metal–air batteries, herein, tobacco-derived N-containing ordered mesoporous carbon(N-OMC) electrocatalysts with different N species distributions are designed. Results indicate that the as-prepared N-OMC with more pyrrolic and pyridinic Ns exhibits much higher activities for the ORR and OER than N-OMC with more graphitic N in both acidic and alkaline media, suggesting that the increase of pyrrolic and pyridinic Ns favors the improvement of ORR and OER activities of the N-containing carbon catalysts, and showing a great potential for the designing of more effective, lower-cost ORR and OER bifunctional electrocatalysts for future regenerative fuel cells and rechargeable metal–air batteries.

Three-dimensional spatial structure of the macro-pores and flow simulation in anthracite coal based on X-ray μ-CT scanning data

The three-dimensional(3 D) structures of pores directly affect the CH4 flow.Therefore,it is very important to analyze the3 D spatial structure of pores and to simulate the CH4 flow with the connected pores as the carrier.The result shows that the equivalent radius of pores and throats are 1-16 μm and 1.03-8.9 μm,respectively,and the throat length is 3.28-231.25 μm.The coordination number of pores concentrates around three,and the intersection point between the connectivity function and the X-axis is 3-4 μm,which indicate the macro-pores have good connectivity.During the single-channel flow,the pressure decreases along the direction of CH4 flow,and the flow velocity of CH4 decreases from the pore center to the wall.Under the dual-channel and the multi-channel flows,the pressure also decreases along the CH4 flow direction,while the velocity increases.The mean flow pressure gradually decreases with the increase of the distance from the inlet slice.The change of mean flow pressure is relatively stable in the direction horizontal to the bedding plane,while it is relatively large in the direction perpendicular to the bedding plane.The mean flow velocity in the direction horizontal to the bedding plane(Y-axis) is the largest,followed by that in the direction horizontal to the bedding plane(X-axis),and the mean flow velocity in the direction perpendicular to the bedding plane is the smallest.

Carboniferous tectono-magmatic evolution of the northern Luliang arc: evidence from geochemistry and petrography of Carboniferous volcanic rocks in the northern Luliang Uplift,NW China

The Northern Junggar Basin experienced extensive subduction and a complex tectono-magmatic evolution during the Late Paleozoic,resulting in a heterogeneous distribution of volcanic rocks in the Junggar Basin.In this study,the Carboniferous tectono-magmatic evolution of the northern Luliang arc was described by exploring the petrography and geochemistry of Carboniferous volcanic rocks collected from well Y-2 and outcrop WW' in the northern Luliang Uplift.The distribution,types,and formation ages of these volcanic rocks were characterized and the volcanic sequence in well Y-1 was divided into upper and lower parts according to vertical variations in selected geochemical data.Then the petrogenesis and tectonic settings of different volcanic rocks were evaluated and this was used to infer the tectonomagmatic evolution of the northern Luliang arc during the Carboniferous.The results indicate that:(1) Carboniferous high-K calc-alkali andesite-dacite associations are distributed in the west of the northern Luliang Uplift,and Lower Carboniferous calc-alkali basalt-dacite-rhyolite assemblages are preserved in its east.(2) The intermediateacid volcanic rocks in wells Y-1 and Y-2 were derived from calc-alkali basaltic magma through melting of the juvenile lower crust,and geochemical variations indicate increasing addition of slab melting in a subduction-related arc environment.The bimodal volcanic rocks from outcrop WW' were derived from lithospheric underplating of basaltic magma in an intra-arc extensional setting.(3) The closure of the eastern Keramaili Oceanic basin occurred before the Early Carboniferous,and the tectono-magmatic difference between the east and the west of the northern Luliang Uplift appeared before the Carboniferous period.

Numerical analysis of matrix swelling and its effect on microstructure of digital coal and its associated permeability during CO_(2)-ECBM process based on X-ray CT data

Matrix swelling effect will cause the change of microstructure of coal reservoir and its permeability,which is the key factor affecting the engineering effect of CO_(2)-ECBM technology.The Sihe and Yuwu collieries are taken as research objects.Firstly,visualization reconstruction of coal reservoir is realized.Secondly,the evolution of the pore/fracture structures under different swelling contents is discussed.Then,the influence of matrix phase with different swelling contents on permeability is discussed.Finally,the mechanism of swelling effect during the CO_(2)-ECBM process is further discussed.The results show that the intra-matrix pores and matrix-edge fractures are the focus of this study,and the contacting area between matrix and pore/fracture is the core area of matrix swelling.The number of matrix particles decreases with the increase of size,and the distribution of which is isolated with small size and interconnected with large size.The swelling effect of matrix particles with larger size has a great influence on the pore/fracture structures.The number of connected pores/fractures is limited and only interconnected in a certain direction.With the increase of matrix swelling content,the number,porosity,width,fractal dimension,surface area and volume of pores/fractures decrease,and their negative contribution to absolute permeability increases from 0.368% to 0.633% and 0.868%-1.404%,respectively.With the increase of swelling content,the number of intra-matrix pores gradually decreases and the pore radius becomes shorter during the CO_(2)-ECBM process.The matrix continuously expands to the connected fractures,and the width of connected fractures gradually shorten.Under the influence of matrix swelling,the bending degree of fluid flow increases gradually,so the resistance of fluid migration increases and the permeability gradually decreases.This study shows that the matrix swelling effect is the key factor affecting CBM recovery,and the application of this effect in CO_(2)-ECBM process can be discussed.

A comparative single-pulse shock tube experiment and kinetic modeling study on pyrolysis of cyclohexane,methylcyclohexane and ethylcyclohexane

The pyrolysis of cyclohexane,methylcyclohexane,and ethylcyclohexane have been studied behind reflected shock waves at pressures of 5 and10 bar and at temperatures of 930-1550 K for 0.05%fuel diluted by Argon.A single-pulse shock tube(SPST)is used to perform the pyrolysis experiments at reaction times varying from 1.65 to 1.74 ms.Major products are obtained and quantified using gas chromatography analysis.A flame ionization detector and a thermal conductivity detector are used for species identification and quantification.Kinetic modeling has been performed using several detailed and lumped chemical kinetic mechanisms.Differences in modeling results among the kinetic models are described.Reaction path analysis and sensitivity analysis are performed to determine the important reactions controlling fuel pyrolysis and their influence on the predicted concentrations of reactant and product species profiles.The present work provides new fundamental knowledge in understating pyrolysis characteristics of cyclohexane compounds and additional data set for detailed kinetic mechanism development.

Numerical simulation of enhancing coalbed methane recovery by injecting CO_2 with heat injection

The technology used to enhance coalbed methane(CBM) recovery by injecting CO_2(CO_2-ECBM) with heat, combining heat injection with CO_2 injection, is still in its infancy; therefore, theoretical studies of this CO_2-ECBM technology should be perused. First, the coupling equations of the di usion–adsorption–seepage–heat transfer fields of gas are established. The displacement processes under di erent pressures and temperatures are simulated by COMSOL. Finally, the displacement effects, a comparison of the CO_2 storage capacity with the CH_4 output and the e ective influencing radius of CO_2 injection are analyzed and discussed. The results show that(1) the displacement pressure and temperature are two key factors influencing the CH_4 output and the CO_2 storage capacity, and the increase in the CO_2 storage capacity is more sensitive to temperature and pressure than the CH_4 output.(2) The gas flow direction is from the injection hole to the discharge hole during the displacement process, and the regions with high velocity are concentrated at the injection hole and the discharge hole.(3) A reduction in the CH_4 concentration and an increase in the CO_2 concentration are obvious during the displacement process.(4) The e ective influencing radius of injecting CO_2 with heat increases with the increase in time and pressure. The relationship between the e ective influencing radius and the injection time of CO_2 has a power exponential function, and there is a linear relationship between the functional coe cient and the injection pressure of CO_2. This numerical simulation study on enhancing CBM recovery by injecting CO_2 with heat can further promote the implementation of CO_2-ECBM project in deep coal seams.

Simulation of Paleotectonic Stress Fields and Distribution Prediction of Tectonic Fractures at the Hudi Coal Mine, Qinshui Basin

Study on tectonic fractures based on the inversion of tectonic stress fields is an effective method. In this study, a geological model was set up based on geological data from the Hudi Coal Mine, Qinshui Basin, a mechanical model was established under the condition of rock mechanics and geostress, and the finite element method was used to simulate the paleotectonic stress field. Based on the Griffith and Mohr-Coulomb criterion, the distribution of tectonic fractures in the Shanxi Formation during the Indosinian, Yanshanian, and Himalayan period can be predicted with the index of comprehensive rupture rate. The results show that the acting force of the Pacific Plate and the India Plate to the North China Plate formed the direction of principal stress is N-S, NW - SE, and NE - SW, respectively, in different periods in the study area. Changes in the direction and strength of the acting force led to the regional gradients of tectonic stress magnitude, which resulted in an asymmetrical distribution state of the stress conditions in different periods. It is suggested that the low-stress areas are mainly located in the fault zones and extend along the direction of the fault zones. Furthermore, the high-stress areas are located in the junction of fold belts and the binding site of multiple folds. The development of tectonic fractures was affected by the distribution of stress intensity and the tectonic position of folds and faults, which resulted in some developed areas with level I and II. There are obvious differences in the development of tectonic fractures in the fold and fault zones and the anticline and syncline structure at the same fold zones. The tectonic fractures of the Shanxi Formation during the Himalayan period are more developed than those during the Indosinian and Yanshanian period due to the superposition of the late tectonic movement to the early tectonic movement and the differences in the magnitude and direction of stress intensity.

Characteristics of high-rank coal structure parallel and perpendicular to the bedding plane via NMR and X-ray CT

Pores and fractures and their connectivity play a significant role in coalbed methane production.To investigate the growth characteristics and connectivity of pores and fractures in coal parallel and perpendicular to the bedding plane,the pores and fractures of high-rank coal samples collected from the southern Qinshui Basin were measured by low-field nuclear magnetic resonance,X-ray-computed tomography and field emission scanning electron microscopy.Then,the determinants of their connectivity were further discussed.The results show that the high-rank coal samples have similar pore size distributions both parallel and perpendicular to the bedding plane.They primarily contain mesopores(2-50 nm in width),followed by macrospores(> 50 nm in width).The research indicated that the high-rank coal connectivity parallel to the bedding plane is significantly better than that perpendicular to the bedding plane.The connectivity of high-rank coal is mainly determined by throats,and the orientation of the pores and fractures.The two connectivity modes in high-rank coal are "pore connectivity," in which the throats are mainly pores with a low coordination number,and "microfissure connectivity",in which the throats are mainly microfissures with a high coordination number.

Temperature field distribution of burnt surrounding rock in UCG stope

In order to study temperature field distribution in burnt surrounding rock and to determine ranges of burnt surrounding rock, coal-wall coking cycle and heat influence in the underground coal gasification(UCG) stope, based on the Laplace transform and inversion formula, we studied the temperature analytical solution of one-dimensional unsteady heat conduction for multi-layer overlying strata under the first and the forth kinds of boundary conditions, and we also carried out a numerical simulation of twodimensional unsteady heat conduction by the COMSOL multiphysics. The results show that when the boundary temperature of surrounding rock has a linear decrease because of a directional movement of heat source in the UCG flame working face, the temperature in surrounding rock increases first and then decreases with time, the peak of temperature curve decreases gradually and its position moves inside surrounding rock from the boundary. In the surrounding rock of UCG stope, there is an envelope curve of temperature curve clusters. We analyzed the influence of thermophysical parameters on envelope curves and put forward to take envelope curve as the calculation basis for ranges of burnt surrounding rock, coal-wall coking cycle and heat influence. Finally, the concrete numerical values are given by determining those judgement standards and temperature thresholds, which basically tally with the field geophysical prospecting results.

Characteristics of water contamination in abandoned coal mines:a case study on Yudong River area,Kaili,Guizhou Province,China

The seasonal and spatial changes in the chemical composition of the water in abandoned mine drainages and rivers in Yudong River area in the years of 2017-2018 were analyzed.The effects of mine water drainage on the seasonality and physicochemical properties of the river water after mine closure were evaluated,and the feasibility of irrigation using river water and the degree of pollution to farmland were assessed using the Water Quality Standard for Farmland Irrigation.The results show that the mine water has low pH value(<3.5-4)and high levels of total hardness,SO_(4)^(2−),Fe,Al,and Zn.In addition,the pH of the mine water is negatively correlated with the presence of other metal ions.The correlation coefficient between the chemical oxygen demand(COD)and Fe reached 0.989.While the pollution levels of Pinglu and Baishui rivers were low,the confluence region of the two rivers was seriously polluted.However,only the levels of Fe and Cd slightly exceeded the Surface Water Environmental Quality Standard after the confluence of Yudong and Chongan rivers.Overall,the heavy pollution type of the confluent river is consistent with mine water pollution.The water quality is slightly better in the dry season compared than in the high-water period.Sulfate and Fe content decreased by 39 and 16 mg/L,respectively,and Cd content decreased two-fold.Despite these findings,this study shows that from 2017 to 2018,the pH and Cd content of the rivers at the confluence exceeded the irrigation limit and the water quality continued to deteriorate,which may pose a soil contamination risk.Long-term use of the river for irrigation water may cause toxic elements such as Cd,Fe,Mn,SO_(4)^(2−),Al,and F-to enter the food chain,thereby endangering the life and health of villagers in Yudong River area.

A novel wastewater cleaning system for the stone-crushing and sand-making process

The nature of the slurry from the stone-crushing and sand-making processes is analyzed to develop a novel separation process.The process comprises hydro-cyclone separation followed by screening of the fines,clarification,and filtration.Recovering fine sand and clean wastewater for recycle is demonstrated.The +0.045 mm fine sand fraction and à0.045 mm ultra-fine clay in the slurry are separated and recovered.Fine sand that was previously lost and wasted is now recoverable.The cleaned and reused water is as much as 94% of the total.

Cake forming and filtering time in the spiral discharging fine coal filtering centrifuge

Based on the realization of moving-bed cake filtering, the concepts of static-bed filtering time and moving-bed fil- tering time in the helical-conveyor fine coal filtering centrifuge were proposed, and the mathematic relations between the time defined and the main factors related were studied in detail. The results show that the static-bed filtering time is the function of the spiral heads and the rotation rate deference between the spiral and the porous drum, while the moving-bed filtering time is the function of the cone angle of the porous drum, the radius of the porous drum, the spiral angle, and the rotation rate deference. The functions deduced are of great significance for fine coal filtering centrifuge＇s parameters determining and optimizing. It is shown that the filtering centrifuge with smaller spiral angle, smaller rotation rate deference, and smaller cone angle may do a better job for fine coal dewatering.

New Discovery on Methane Adsorption Change of Coal due to Sc-CO_2 Extraction during CO_2-ECBM

Objective The technical development of COstorage and enhanced coalbed methane(CO-ECMB) recovery requires reliable and detailed information on gas adsorption. In most cases of geo-storage COis injected in the supercritical state(Tc=31.1 °C, Pc=7.38 MPa). In the supercritical state, the fluid of supercritical CO(Sc-CO) can not only react with minerals under the condition of water, but also extract small organic molecules from coal

Solid superacid-catalyzed hydroconversion of an extraction residue from Lingwu bituminous coal

A solid superacid was prepared as a catalyst. The catalyst was characterized by ammonia temperature- programmed desorption, surface property measurement, and analyses with scanning electron micros- copy and Fourier transform infrared spectrometry. A extraction residue from Lingwu subbituminous coal was subject to non-catalytic and catalytic hydroconversion using cyclohexane as the solvent under pres- surized hydrogen at 300 ℃ for 3 h. The results show that the total yield of petroleum ether-extractable arenes from catalytic hydroconversion is much higher than that from non-catalytic hydroconversion. The cleavage of Car-Cask bonds in the residue could significantly proceed during catalytic hvdrncnnvarsion

New Discovery on Supercritical CO2-H2O Treated Coal： Pore Structure and Methane Adsorption

Nowadays, the governments and worldwide energy and environmental scientists have been focusing on CO2 enhanced coalbed methane recovery （CO2-ECBM） to reduce greenhouse gas emissions and to increment coalbed methane production. Previous researches have confirmed that CO2 can react with minerals in coal seams to transform the permeability of coal. However, few studies have paid attention to the influence of the reaction of CO2 with minerals on the pore distribution and methane adsorption of coals.

Magnetic Fe_(2)O_(3)/biochar composite prepared in a molten salt medium for antibiotic removal in water

The large-scale use of antibiotics is causing serious water pollution problems,and it is of great significance to develop new technologies to remove antibiotics from water.As an environmentally friendly and economical adsorption material,carbon derived from biomass is a low-cost and feasible material for removing antibiotics in sewage,but the current removal efficiencies are not high enough for large-scale practical application.In this study,poplar wood chips are used as raw material,and a magnetic biochar is prepared by co-pyrolysis of poplar wood chips and FeCl_(3)/CaCl_(2)mixed molten salt.X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FTIR),N_(2)-isothermal adsorption and desorption,X-ray photoelectron spectroscopy(XPS)and scanning electron microscope(SEM)techniques showed the successful synthesis of Fe_(2)O_(3)/bioC composite.In-situ formed Fe_(2)O_(3)makes the biochar possess the characteristic of superparamagnetic,which is conducive to the recycling of biochar.Due to the etching effect of the molten salts,rough surface was formed on Fe_(2)O_(3)/bioC,result-ing in a maximum norfloxacin(NOR)adsorption ability up to 38.77 mg g^(−1)at pH 6.0.The NOR adsorption behavior on Fe_(2)O_(3)/bioC followed the pseudo second order kinetic model and the equilibrium data was best fitted the Langmuir model.In addition,the adsorption process of NOR on Fe_(2)O_(3)/bioC was thermodynamically spontaneous.The results show that this low-cost and reusable magnetic biochar has the potential for rapid and efficient removal of antibiotic from aqueous solution.

Diagenesis of shale and its control on pore structure, a case study from typical marine, transitional and continental shales

Due to discrepancies in pore structure,the productivity of shale gas reservoirs under different diagenesis stages varies greatly.This study discussed the controlling of sedimentation and diagenesis on shale pore structure in typical marine,transitional,and continental shales,respectively.Continental shale samples from the Shuinan Formation,Jiaolai Basin,transitional shale samples from the Taiyuan,Shanxi and Xiashihezi Formations,Ordos Basin,and marine shale samples from the Longmaxi Formation,Sichuan Basin,were collected.Scanning electron microscope with argon ion polishing,high-pressure mercury injection,and low-temperature nitrogen adsorption experiments were conducted to acquire pore structure parameters.And the diagenetic stage of the reservoir was classified according to thermal maturity,organic geochemical parameters,and mineral composition.Our results exhibit that continental,transitional,and marine shales are period A,period B of the middle diagenetic stage,and the late diagenetic stage,respectively.For pore structure,micropore(0–2 nm)and mesopore(2–50 nm)controlled pore volume and specific surface area of transitional and marine shales,and specific surface area of continental shale have similar results,while micropore,mesopore,and macropore(>50 nm)all have a significant proportion of pore volume in continental shale.The pore structure characteristics and controlling factors exhibit a pronounced difference in different diagenesis stages,the compaction and cementation in period A of the middle diagenesis stage is relatively weak,intergranular pore and interlayer pore of clay minerals are well preserved,and moldic pore and dissolved pore developed as well;organic matter is in high maturity in period B of the middle diagenesis stage,organic matter pore developed correspondingly,while the intergranular pore developed poorly affected by compaction,notably,the carbonate is negligible in transitional shale,and the interlayer pore of clay minerals are well preserved with weak cementation;while dissolution and metasomatism controlled the pore structure in the late diagenesis stage in marine shale,the primary pores were poorly preserved,and the organic matter pore and carbonate dissolved pore developed.Results from this work are of a specific reference for shale gas development under different diagenesis stages.

Effective remediation of organic-metal co-contaminated soil by enhanced electrokinetic-bioremediation process

This work investigates the influence of electrokinetic-bioremediation(EK-BIO)on remediating soil polluted by persistent organic pollutants(POPs)and heavy metals(mainly Cu,Pb and Ni),originated from electronic waste recycling activity.The results demonstrate that most of POPs and metals were removed from the soil.More than 60%of metals and 90%of POPs in the soil were removed after a 30-day EK-BIO remediation assisted by citrate.A citrate sodium concentration of 0.02 g/L was deemed to be suitable because higher citrate did not significantly improve treatment performance whereas increasing dosage consumption.Citrate increased soil electrical current and electroosmotic flow.After remediation,metal residues mainly existed in stable and low-toxic states,which could effectively lower the potential hazard of toxic metals to the surrounding environment and organisms.EK-BIO treatment influenced soil microbial counts,dehydrogenase activity and community structure.

Effective alleviation of Cd stress to microbial communities in mining reclamation soils by thiourea-modified biochar amendment

Reclaimed soils in mining area usually display low fertility and present Cd stress.The amendment of modified biochar effectively fixes Cd in soils,enhances soil fertility,and reduces Cd stress in soil microorganisms.However,the effect of thiourea-modified biochar(TBC)on microbial adaptability to Cd stress in mining reclamation soils is still unclear.The present work studied the Cd immobilization and microbial community changes in a mining reclamation soil displaying extreme Cd contamination under TBC amendment.The results indicated that the amendment of TBC significantly enhanced(P<0.05)soil pH,the content of available phosphorus(AP),and the activities of urease and polyphenol oxidase by 1.3%,463.4%,54.4%,and 84.0%,respectively,compared to the control without amendment.The amount of toxicity characteristic leaching procedure-extracable Cd decreased(P<0.05)by 68.0%in the TBC-amended soil compared with the unamended soil.The structure of soil microbiota was reorganized and the alpha diversity index was increased in the TBC treatment.The TBC amendment increased the relative abundances of Proteobacteria,Bacteroidota,and Zoopagomycota,which were strongly associated(P<0.01)with higher soil pH and AP.Structural equation model results demonstrated that Cd immobilization was directly influenced by soil pH,AP,and urease,and indirectly affected by bacterial structure in the TBC treatment.The TBC amendment can effectively improve the structural composition of soil bacteria under Cd stress and enhance the pathways of decreasing soil Cd availability as well.The results might facilitate the development of in-situ remediation programs in Cd-contaminated soils in the future.

Electronic and optical properties of single-layer MoS2

The electronic structures of a MoS2 monolayer are investigated with the all-electron first principle calculations based on the density functional theory （DFT） and the spin-orbital couplings （SOCs）. Ore＂ results show that the monolayer MoS2 is a direct band gap semiconductor with a band gap of 1.8 eV. The SOCs and d-electrons in Mo play a very significant role in deciding its electronic and optical properties. Moreover, electronic elementary excitations are studied theoretically within the diagram- matic self-consistent field theory. Under random phase approximation, it shows that two branches of plasmon modes can be achieved via the conduction-band transitions due to the SOCs, which are different from the plasmons in a two-dimensional electron gas and graphene owing to the quasi-linear energy dispersion in single-layer MoS2. Moreover, the strong optical absorption up to 105 cm-1 and two optical absorption edges I and II can be observed. This study is relevant to the applications of monolayer MoS2 as an advanced photoelectronic device.