Development of reaction-tailored electrocatalysts is becoming increasingly important as energy and environment are among key issues governing our sustainable future.Electrocatalysts are inherently optimized for applic...Development of reaction-tailored electrocatalysts is becoming increasingly important as energy and environment are among key issues governing our sustainable future.Electrocatalysts are inherently optimized for application towards reactions of interest in renewable energy,such as those involved in water splitting and artificial photosynthesis,owing to its energy efficiency,simple fabrication,and ease of operation.In this view,it is important to secure logical design principles for the synthesis of electrocatalysts for various reactions of interest,and also understand their catalytic mechanisms in the respective reactions for improvements in further iterations.In this review,we introduce several key methods of scanning electrochemical microscopy(SECM)in its applications towards electrocatalysis.A brief history and a handful of seminal works in the SECM field is introduced in advancing the synthetic designs of electrocatalysts and elucidation of the operating mechanism.New developments in nano-sizing of the electrodes in attempts for improved spatial resolution of SECM is also introduced,and the application of nanoelectrodes towards the investigation of formerly inaccessible single catalytic entities is shared.展开更多
The kinetics of the surface reactions of single crystal Ni3Al and polycrystal line Ni3Al0.00052 wt% B with water vapor or oxygen was investigated using XPS. Both reactions initiate at less than 1.5×10-6 Pa.s expo...The kinetics of the surface reactions of single crystal Ni3Al and polycrystal line Ni3Al0.00052 wt% B with water vapor or oxygen was investigated using XPS. Both reactions initiate at less than 1.5×10-6 Pa.s exposure. The reaction of Ni3Al does not saturote with water vapor at 0.43 Pa.s; with oxygen at 8.4×10-2 Pa.s and the oxide formed is Al2O3. The kinetics of these reactions can be used to eaplain the different ductility behavior of Ni3Al-based alloys in various environment.展开更多
The interaction of water vapor and oxygen with TiAI-based alloy has been studied with Auger electron spectroscopy and X-ray photoelectron spectroscopy. The results indicate that both surface reactions initiate at a ve...The interaction of water vapor and oxygen with TiAI-based alloy has been studied with Auger electron spectroscopy and X-ray photoelectron spectroscopy. The results indicate that both surface reactions initiate at a very short exposure (about 6×10-7 Pa·s) and the oxides Al2O3 and TiO2 form in the surface reactions. In the oxidizing reaction, the water vapor reacts firstly with Al, and then reacts with Ti after certain exposure. The surface reaction of Al with water vapor may be responsible for the environmental embrittlement at room temperature in TiAI-based alloy.展开更多
The adsorption of pentachlorophenol （PCP） onto quartz, kaolinite, illite, montmorillonite and iron oxides has been investigated by batch equilibrium techniques. The pH-dependent isotherms are curves with peak values...The adsorption of pentachlorophenol （PCP） onto quartz, kaolinite, illite, montmorillonite and iron oxides has been investigated by batch equilibrium techniques. The pH-dependent isotherms are curves with peak values, the position of which is at about pH = 5-6 depending on the mineral species. Based on distribution of both speciation of surface hydroxyls on minerals and PCP in solution a surface reaction model involving surface complexation and surface electrostatic attraction is presented to fit the pH-dependent isotherms, and both reaction constants are calculated. The results show that on quartz and phyllosilicate minerals the predominant adsorption reaction is surface complexation, meanwhile both of surface electrostatic attraction and surface complexation are involved on the iron oxide minerals. The reaction constants of surface electrostatic adsorption are usually one to three orders in magnitude, larger than that of surface complexation. The concentration-dependent isotherms can be well fitted by Langmnir equation with the correlation coefficient R〉0.93 for kaolinite and iron oxides. The maximum adsorption is found in the order： hematite 〉 lepidocrocite 〉 goethite 〉 kaolinite 〉 quartz 〉 montmorillonite ≈ illite, which can be interpreted by consideration of both reaction mechanism and surface hydroxyl density. The significant adsorption of PCP onto mineral surfaces suggests that clay and iron oxide minerals will play an important role as HIOCs are adsorbed in laterite or latertoid soil, which is widespread in South China.展开更多
The surface reaction of Co 3Ti alloys (with and without Fe) with water vapor was investigated by using Auger electron spectroscopy (AES). The results showed that the rate of the surface reaction is much lower in Co 21...The surface reaction of Co 3Ti alloys (with and without Fe) with water vapor was investigated by using Auger electron spectroscopy (AES). The results showed that the rate of the surface reaction is much lower in Co 21 5Ti 3Fe alloy as compared with Co 3Ti (Co 23Ti) alloy. The surface reaction of Co 21 5Ti 3Fe alloy with water vapor saturates at exposure of 2×10 -3 Pa·s, but it does not saturate even at 0 1 Pa·s exposure for Co 3Ti alloy without Fe. The results also indicated that the kinetic of the surface reaction of Co 21 5Ti 3Fe with water vapor is much smaller than that of Co 3Ti at the same exposure. All the above results illustrate that the suppression of environmental embrittlement by addition of Fe to Co 3Ti alloy is attributed to its reduction of the surface reaction kinetics with water vapor.展开更多
Carrier dynamics and surface reaction are two critical processes for determining the performance of photocatalytic reaction.Highly designable polymer-based photocatalysts have shown promising protectives in energetic ...Carrier dynamics and surface reaction are two critical processes for determining the performance of photocatalytic reaction.Highly designable polymer-based photocatalysts have shown promising protectives in energetic and environmental applications.In this prospective,we first distinguished the differences of physiochemical properties between polymer-based semiconductors and traditional inorganic semiconductors.Then,the effects of single-atom sites on the charge dynamics and reaction kinetics of polymer-based photocatalysts are further elaborated.Time(excitation)-space(wavefunction)population analysis,which can provide relevant information to clarify the structure-excitation relationships after introducing the single atom sites was also reviewed.In the future,with the further development of artificial intelligence,the establishment of an energy function with a regression accuracy close to or reaching the level of density functional theory is highly desired to infer the energetic diagram of the photocatalytic systems at the excited states.Furthermore,coordination structures,interaction with inorganic semiconductors,photocatalytic stability and solvent effects should also be carefully considered in the future studies of polymer-based photocatalyst.展开更多
The effect of boron doping on the sensitivity to environmental embrittlement of Ni3Al-based alloys was investigated in this paper. The results show that the ductilizing effect of boron in Ni3Al is partly to suppress ...The effect of boron doping on the sensitivity to environmental embrittlement of Ni3Al-based alloys was investigated in this paper. The results show that the ductilizing effect of boron in Ni3Al is partly to suppress moisture-induced hydrogen embrittlement.The mechanism of this suppressing effect of boron relates to its severely decreasing the hydrogen diffusivity by boron segregated at the grain boundaries. The surface reaction of Fe3Al with water vapor and oxygen was experimentally confirmed by AES and XPS analysis. The kinetics of these reactions can be used to explain the different ductility behavior of aluminides in various environments.展开更多
The anion kaolinite surface interactions and AuS - adsorption onto the surfaces of kaolinite were studied using the self consistent field discrete variation (SCF-X α-DV) method.Electronic structure and energies ...The anion kaolinite surface interactions and AuS - adsorption onto the surfaces of kaolinite were studied using the self consistent field discrete variation (SCF-X α-DV) method.Electronic structure and energies of the system of anion AuS - adsorbed on an atomic cluster of kaolinite were calculated.The results show that the systems with lower total energy are those AuS - adsorbed on the edge surfaces,which indicates that the systems of adsorption of AuS - on the edges are more stable relative to those adsorbed on the basal plane.On the other hand,bond order data suggest that significant shifting of atomic charge and the overlapping of electronic cloud between Au (Ⅰ) of the AuS - and the surface ions of kaolinite would take place in the systems with AuS - being adsorbed on the edges,especially at the site near Al octahedra.Therefore,it can be concluded that edge sites will dominate the complexation reactions of the surfaces of kaolinite,with negligible contributions from other functional groups on the basal plane,which are dominated by either siloxane sites in silica layers or aluminol sites in gibbsite layers.展开更多
In this work,we revisited the single-step synthesis of CdE(E=S,Se,and Te)quantum dots(QDs).Powdered CdO and elemental chalcogen were directly used for heating-up synthesis.Firstly,the in situ dissolution of the solid ...In this work,we revisited the single-step synthesis of CdE(E=S,Se,and Te)quantum dots(QDs).Powdered CdO and elemental chalcogen were directly used for heating-up synthesis.Firstly,the in situ dissolution of the solid precursors and related QD formation channels were preliminarily investigated.In general,QDs were generated from homogeneous reactions between dissolved cadmium and chalcogen precursors in bulk solution.We found that,during single-step synthesis,both the dissolution of CdO and selenium proceeded faster than their ex situ dissolution respectively.To explain this result,we proposed the existence of extra surface reaction channels for QD formation.That is,QDs could also be generated via on-surface reactions between the solid precursors and the dissolved counter precursors(as“ligands”).The happening of these extra surface reactions would increase the overall dissolution rate of CdO and selenium.Further,the circulation of oleic acid which is peculiar to such single-step synthesis should also partly account for the accelerated dissolution of CdO.Finally,by comparing with two-step synthesis using pre-dissolved CdO,we presented that such single-step synthesis was reliable in making uniform CdE QDs with good reproducibility.Our work reaffirmed the great potential of this single-step strategy in cost-effective synthesis of monodisperse QDs.Moreover,the ligand-promoted surface reaction channels would be applicable in solution-phase synthesis of metal chalcogenide nanocrystals from solid precursors.展开更多
Although photocatalytic water splitting has excellent potential for converting solar energy into chemical energy,the challenging charge separation process and sluggish surface catalytic reactions significantly limit p...Although photocatalytic water splitting has excellent potential for converting solar energy into chemical energy,the challenging charge separation process and sluggish surface catalytic reactions significantly limit progress in solar energy conversion using semiconductor photocatalysts.Herein,we demonstrate a feasible strategy involving the surface assembly of cobalt oxide species(CoO_(x))on a visible-light-responsive Cd_(0.9)Zn_(0.1)S(CZS)photocatalyst to fabricate a hierarchical CZS@CoO_(x) heterostructure.The unique hierarchical structure effectively accelerates the directional transfer of photogenerated charges,reducing charge recombination through the smooth interfacial heterojunction between CZS and CoO_(x),as evidenced by photoluminescence(PL)spectroscopy and various electrochemical characterizations.The surface cobalt species on the CZS material also act as efficient cocatalysts for photocatalytic hydrogen production,with activity even higher than that of noble metals.The well-defined CZS@CoO_(x) heterostructure not only enhances the interfacial separation of photoinduced charges,but also improves surface catalytic reactions.This leads to superior photocatalytic performances,with an apparent quantum efficiency of 20%at 420 nm for visible-light-driven hydrogen generation,which is one of the highest quantum efficiencies measured among noble-metal-free photocatalysts.Our work presents a potential pathway for controlling complex charge separation and catalytic reaction processes in photocatalysis,guiding the practical development of artificial photocatalysts for successful transformation of solar to chemical energy.展开更多
Out-of-pile tritium release experiments were performed on Li4 Si O4 pebbles produced from lithium hydroxide under various compositions of sweep gas(He, 1.1% H2/He) and environmental moisture conditions. The experiment...Out-of-pile tritium release experiments were performed on Li4 Si O4 pebbles produced from lithium hydroxide under various compositions of sweep gas(He, 1.1% H2/He) and environmental moisture conditions. The experimental results indicate that tritium gas can be released directly from "dry" Li4 Si O4 under pure He gas. This phenomenon did not happen on "wet" samples, which means that the chemical form of released tritium is sensitive to moisture. Adding H2 to sweep gas may increase the overall desorption rate of tritium gas through H2 isotope exchange reaction, which occurs at a lower temperature than those of directly released tritium gas. Yet, the threshold of the H2 isotope exchange reaction is higher than the desorption reaction of tritiated water. Consequently, the effect of H2 isotope exchange reaction would reduce significantly on water adsorbed Li4 Si O4 samples.展开更多
The catalysis technology of propylene dimerization to form 4-methyl-1-pentene(4MP1)using a Cu-K/K_(2)CO_(3) solid base catalyst is a well-known heterogeneous catalytic reaction.In this study,the intrinsic kinetics of ...The catalysis technology of propylene dimerization to form 4-methyl-1-pentene(4MP1)using a Cu-K/K_(2)CO_(3) solid base catalyst is a well-known heterogeneous catalytic reaction.In this study,the intrinsic kinetics of propylene dimerization were studied in a fixed-bed continuous reactor.Internal and external diffusion during the dimerization reaction experiments were eliminated by adjusting the flow rate of the carrier gas and the particle size of the catalyst support.Then,the concentration changes of each substance at the outlet of the catalyst bed under different residence times were investigated.Moreover,the suitable reaction kinetics equations was derived using the Langmuir Hinshelwood-Hougen-Watson kinetic model.Finally,the activation energy for each reaction involved in the dimerization reaction was calculated.The activation energies of 4MP1,branched by-products,and 1-hexene were 115.0,150.8,and 177.4 kJ/mol,respectively.The effect of process conditions on propylene dimerization with solid base catalysts was studied through kinetic model simulation.By comparing the theoretical values obtained from the simulation with the experimental results,the applicability and accuracy of the kinetic model were verified.展开更多
Removal of brittle materials in the brittle or ductile mode inevitably causes damaged or strained surface layers containing cracks, scratches or dislocations. Within elastic deformation, the arrangement of each atom c...Removal of brittle materials in the brittle or ductile mode inevitably causes damaged or strained surface layers containing cracks, scratches or dislocations. Within elastic deformation, the arrangement of each atom can be recovered back to its original position without any defects introduced. Based on surface hydroxylation and chemisorption theory, material removal mechanism of quartz glass in the elastic mode is analyzed to obtain defect-free surface. Elastic contact condition between nanoparticle and quartz glass surface is confirmed from the Hertz contact theory model. Atoms on the quartz glass surface are removed by chemical bond generated by impact reaction in the elastic mode, so no defects are generated without mechanical process. Experiment was conducted on a numerically controlled system for nanoparticle jet polishing, and one flat quartz glass was polished in the elastic mode. Results show that scratches on the sample surface are completely removed away with no mechanical defects introduced, and microroughness(Ra) is decreased from 1.23 nm to 0.47 nm. Functional group Ce — O — Si on ceria nanoparticles after polishing was detected directly and indirectly by FTIR, XRD and XPS spectra analysis from which the chemical impact reaction is validated.展开更多
The aim of this article is to present the effects of transpiration on the unsteady two-dimensional boundary layer flow of non-Newtonian fluid passing through a stretching sheet in the presence of a first order constru...The aim of this article is to present the effects of transpiration on the unsteady two-dimensional boundary layer flow of non-Newtonian fluid passing through a stretching sheet in the presence of a first order constructive/destructive chemical reaction. The upper-convected Maxwell （UCM） model is used here to characterize the non-Newtonian behavior of the fluid. Using similarity solutions, the governing nonlinear partial differential equations are transformed into ordinary ones and are then solved numerically by the shooting method. The flow fields and mass transfer are significantly influenced by the governing parameters. The fluid velocity initially decreases as the unsteadiness parameter increases and the concentration decreases significantly due to the increase in the unsteadiness. The effect of increasing values of transpiration （suction） and the Maxwell parameter is to suppress the velocity field; however, the concentration is enhanced as transpiration （suction） and the Maxwell parameter increase. Also, it is found that the fluid velocity decreases as the magnetic parameter increases; however, the concentration increases in this case.展开更多
To investigate the interaction of the bolt-reinforced rock and the surface support,an analytical model of the convergence-confinement type is proposed,considering the sequential installation of the fully grouted rockb...To investigate the interaction of the bolt-reinforced rock and the surface support,an analytical model of the convergence-confinement type is proposed,considering the sequential installation of the fully grouted rockbolts and the surface support.The rock mass is assumed to be elastic-brittle-plastic material,obeying the linear Mohr-Coulomb criterion or the non-linear Hoek-Brown criterion.According to the strain states of the tunnel wall at bolt and surface support installation and the relative magnitude between the bolt length and the plastic depth during the whole process,six cases are categorized upon solving the problem.Each case is divided into three stages due to the different effects of the active rockbolts and the passive surface support.The fictitious pressure is introduced to quantify the threedimensional(3D)effect of the tunnel face,and thus,the actual physical location along the tunnel axis of the analytical section can be considered.By using the bolt-rock strain compatibility and the rocksurface support displacement compatibility conditions,the solutions of longitudinal tunnel displacement and the reaction pressure of surface support along the tunnel axis are obtained.The proposed analytical solutions are validated by a series of 3D numerical simulations.Extensive parametric studies are conducted to examine the effect of the typical parameters of rockbolts and surface support on the tunnel displacement and the reaction pressure of the surface support under different rock conditions.The results show that the rockbolts are more effective in controlling the tunnel displacement than the surface support,which should be installed as soon as possible with a suitable length.For tunnels excavated in weak rocks or with restricted displacement control requirements,the surface support should also be installed or closed timely with a certain stiffness.The proposed method provides a convenient alternative approach for the optimization of rockbolts and surface support at the preliminary stage of tunnel design.展开更多
The electrochemical performance of hard carbon in sodium storage is still limited by its poor cycling stability and rate capability because of the sluggish kinetics process.In this study,we use a simple and effective ...The electrochemical performance of hard carbon in sodium storage is still limited by its poor cycling stability and rate capability because of the sluggish kinetics process.In this study,we use a simple and effective method to accelerate the kinetics process by engineering the structure of the electrode to promote its surface and near-surface reactions.This goal is realized by the use of slightly aggregated ultra-small carbon spheres.The large specific surface area formed by the small spheres can provide abundant active sites for electrochemical reactions.The abundant mesopores and macropores derived from the secondary particle piled structure of the carbon spheres could facilitate the transport of electrolytes,shorten the diffusion distance of Na^(+)and accommodate the volume expansion during cycling.Benefiting from these unique structure features,PG700-3(carbon spheres with the diameters of 40-60 nm carbonized at 700℃)exhibits high performance for sodium storage.A high reversible capacity of 163 mAh g^(-1) could be delivered at a current density of 1.0 A g^(-1) after 100 cycles.Interestingly,at a current density of 10.0 A g^(-1),the specific capacity of PG700-3 gradually increases to 140 mAh g^(-1) after 10000 cycles,corresponding to a capacity retention of 112%.Given the enhanced kinetics of SIBs reactions,PG700-3 exhibits an excellent rate capability,i.e.,230 and 138 mAh g^(-1) at 0.1 and 5.0 A g^(-1),respectively.This study provides a facile method to attain high performance anode materials for SIBs.The design strategy and improvement mechanism could be extended to other materials for high rate applications.展开更多
As an alternative to conventional energy conversion and storage reactions,gas-involved electrochemical reactions,including the carbon dioxide reduction reaction(CO_(2)RR),nitrogen reduction reaction(NRR)and hydrogen e...As an alternative to conventional energy conversion and storage reactions,gas-involved electrochemical reactions,including the carbon dioxide reduction reaction(CO_(2)RR),nitrogen reduction reaction(NRR)and hydrogen evolution reaction(HER),have become an emerging research direction and have gained increasing attention due to their advantages of environmental friendliness and sustainability.Various studies have been designed to accelerate sluggish kinetics but with limited results.Most of them promote the reaction by modulating the intrinsic properties of the catalyst,ignoring the synergistic effect of the reaction as a whole.Due to the introduction of gas,traditional liquid-solid two-phase reactions are no longer applicable to future research.Since gas-involved electrochemical reactions mostly occur at the junctions of gaseous reactants,liquid electrolytes and solid catalysts,the focus of future research on reaction kinetics should gradually shift to three-phase reaction interfaces.In this review,we briefly introduce the formation and constraints of the three-phase interface and propose three criteria to judge its merit,namely,the active site,mass diffusion and electron mass transfer.Subsequently,a series of modulation methods and relevant works are discussed in detail from the three improvement directions of‘exposing more active sites,promoting mass diffusion and accelerating electron transfer’.Definitively,we provide farsighted insights into the understanding and research of three-phase interfaces in the future and point out the possible development direction of future regulatory methods,hoping that this review can broaden the future applications of the three-phase interface,including but not limited to gas-involved electrochemical reactions.展开更多
The mechanism of the cycloaddition reaction between singlet dimethyl-silylene carbene and acetone has been investigated with density functional theory, From the potential energy profile, it can be predicted that the r...The mechanism of the cycloaddition reaction between singlet dimethyl-silylene carbene and acetone has been investigated with density functional theory, From the potential energy profile, it can be predicted that the reaction has two competitive dominant reaction pathways. The presented rule of this reaction： the [2＋2] cycloaddition effect between the πorbital of dimethyl-silylene carbene and the π orbital of π-bonded compounds leads to the formation of a twisty four-membered ring intermediate and a planar four-membered ring product; The unsaturated property of C atom from carbene in the planar four-membered ring product,resulting in the generation of CH3-transfer product and silicic bis-heterocyclic compound.展开更多
The intention of the current research is to address the conclusion of non-isothermal heterogeneous reaction on the stagnation-point flow of SWCNT-engine oil and MWCNT-engine oil nanofluid over a shrinking/stretching s...The intention of the current research is to address the conclusion of non-isothermal heterogeneous reaction on the stagnation-point flow of SWCNT-engine oil and MWCNT-engine oil nanofluid over a shrinking/stretching sheet.Further,exemplify the aspect of heat and mass transfer the upshot of magnetohydrodynamics(MHD),thermal radiation,and heat generation/absorption coefficient are exemplified.The bvp4 c from Matlab is pledged to acquire the numerical explanation of the problem that contains nonlinear system of ordinary differential equations(ODE).The impacts of miscellaneous important parameters on axial velocity,temperature field,concentration profile,skin friction coefficient,and local Nusselt number,are deliberated through graphical and numerically erected tabulated values.The solid volume fraction diminishes the velocity distribution while enhancing the temperature distribution.Further,the rate of shear stress declines with increasing the magnetic and stretching parameter for both SWCNT and MWCNT.展开更多
Developing a widely-used reactive force field is meaningful to explore the fundamental reaction mechanism on gas-surface chemical reaction dynamics due to its very high computational efficiency. We here present a stud...Developing a widely-used reactive force field is meaningful to explore the fundamental reaction mechanism on gas-surface chemical reaction dynamics due to its very high computational efficiency. We here present a study of hydrogen and its deuterated molecules dissociation on Pd surfaces based on a full-dimensional potential energy surface （PES） constructed by using a simple second moment approximation reactive force field （SMA RFF）. Although the descriptions of the adsorbate-substrate interaction contain only the dissociation reaction of H2/Pd（111） system, a good transferability of SMA potential energy surface （PES） is shown to investigate the hydrogen dissociation on Pd（100）. Our simulation results show that, the dissociation probabilities of H2 and its deuterated molecules on Pd（111） and Pd（100） surfaces keep non-monotonous variations with respect to the incident energy Ei, which is in good agreement with the previous ab initio molecular dynamics. Furthermore, for the oriented molecules, the dissociation probabilities of the oriented H2 （D2 and T2） molecule have the same orientation dependence behavior as those oriented HD （HT and DT） molecules.展开更多
文摘Development of reaction-tailored electrocatalysts is becoming increasingly important as energy and environment are among key issues governing our sustainable future.Electrocatalysts are inherently optimized for application towards reactions of interest in renewable energy,such as those involved in water splitting and artificial photosynthesis,owing to its energy efficiency,simple fabrication,and ease of operation.In this view,it is important to secure logical design principles for the synthesis of electrocatalysts for various reactions of interest,and also understand their catalytic mechanisms in the respective reactions for improvements in further iterations.In this review,we introduce several key methods of scanning electrochemical microscopy(SECM)in its applications towards electrocatalysis.A brief history and a handful of seminal works in the SECM field is introduced in advancing the synthetic designs of electrocatalysts and elucidation of the operating mechanism.New developments in nano-sizing of the electrodes in attempts for improved spatial resolution of SECM is also introduced,and the application of nanoelectrodes towards the investigation of formerly inaccessible single catalytic entities is shared.
文摘The kinetics of the surface reactions of single crystal Ni3Al and polycrystal line Ni3Al0.00052 wt% B with water vapor or oxygen was investigated using XPS. Both reactions initiate at less than 1.5×10-6 Pa.s exposure. The reaction of Ni3Al does not saturote with water vapor at 0.43 Pa.s; with oxygen at 8.4×10-2 Pa.s and the oxide formed is Al2O3. The kinetics of these reactions can be used to eaplain the different ductility behavior of Ni3Al-based alloys in various environment.
基金sponsored by the National Natural Science Foundation of China under Contract 59771007a key project of the National Natural Science Foundation of China under Contract 59895157
文摘The interaction of water vapor and oxygen with TiAI-based alloy has been studied with Auger electron spectroscopy and X-ray photoelectron spectroscopy. The results indicate that both surface reactions initiate at a very short exposure (about 6×10-7 Pa·s) and the oxides Al2O3 and TiO2 form in the surface reactions. In the oxidizing reaction, the water vapor reacts firstly with Al, and then reacts with Ti after certain exposure. The surface reaction of Al with water vapor may be responsible for the environmental embrittlement at room temperature in TiAI-based alloy.
基金the National Natural Science Foundation of China （grant No. 40373045） the Natural Science Foundation of Guangdong Province, China （grant No. 030461） the Chinese Academy of Sciences Innovation Project （GIGCX-04-02）.
文摘The adsorption of pentachlorophenol （PCP） onto quartz, kaolinite, illite, montmorillonite and iron oxides has been investigated by batch equilibrium techniques. The pH-dependent isotherms are curves with peak values, the position of which is at about pH = 5-6 depending on the mineral species. Based on distribution of both speciation of surface hydroxyls on minerals and PCP in solution a surface reaction model involving surface complexation and surface electrostatic attraction is presented to fit the pH-dependent isotherms, and both reaction constants are calculated. The results show that on quartz and phyllosilicate minerals the predominant adsorption reaction is surface complexation, meanwhile both of surface electrostatic attraction and surface complexation are involved on the iron oxide minerals. The reaction constants of surface electrostatic adsorption are usually one to three orders in magnitude, larger than that of surface complexation. The concentration-dependent isotherms can be well fitted by Langmnir equation with the correlation coefficient R〉0.93 for kaolinite and iron oxides. The maximum adsorption is found in the order： hematite 〉 lepidocrocite 〉 goethite 〉 kaolinite 〉 quartz 〉 montmorillonite ≈ illite, which can be interpreted by consideration of both reaction mechanism and surface hydroxyl density. The significant adsorption of PCP onto mineral surfaces suggests that clay and iron oxide minerals will play an important role as HIOCs are adsorbed in laterite or latertoid soil, which is widespread in South China.
文摘The surface reaction of Co 3Ti alloys (with and without Fe) with water vapor was investigated by using Auger electron spectroscopy (AES). The results showed that the rate of the surface reaction is much lower in Co 21 5Ti 3Fe alloy as compared with Co 3Ti (Co 23Ti) alloy. The surface reaction of Co 21 5Ti 3Fe alloy with water vapor saturates at exposure of 2×10 -3 Pa·s, but it does not saturate even at 0 1 Pa·s exposure for Co 3Ti alloy without Fe. The results also indicated that the kinetic of the surface reaction of Co 21 5Ti 3Fe with water vapor is much smaller than that of Co 3Ti at the same exposure. All the above results illustrate that the suppression of environmental embrittlement by addition of Fe to Co 3Ti alloy is attributed to its reduction of the surface reaction kinetics with water vapor.
基金Mitsubishi Chemical Corporation,JSPS Grant-in-Aid for Scientific Research(B,No.20H02847)Grant-in-Aid for JSPS Fellows(DC2,No.20J13064)+2 种基金National Natural Science Foundation of China(No.21805191)Guangdong Basic and Applied Basic Research Foundation,China(No.2020A1515010982)Shenzhen Stable Support Project,China(No.20200812122947002).
文摘Carrier dynamics and surface reaction are two critical processes for determining the performance of photocatalytic reaction.Highly designable polymer-based photocatalysts have shown promising protectives in energetic and environmental applications.In this prospective,we first distinguished the differences of physiochemical properties between polymer-based semiconductors and traditional inorganic semiconductors.Then,the effects of single-atom sites on the charge dynamics and reaction kinetics of polymer-based photocatalysts are further elaborated.Time(excitation)-space(wavefunction)population analysis,which can provide relevant information to clarify the structure-excitation relationships after introducing the single atom sites was also reviewed.In the future,with the further development of artificial intelligence,the establishment of an energy function with a regression accuracy close to or reaching the level of density functional theory is highly desired to infer the energetic diagram of the photocatalytic systems at the excited states.Furthermore,coordination structures,interaction with inorganic semiconductors,photocatalytic stability and solvent effects should also be carefully considered in the future studies of polymer-based photocatalyst.
文摘The effect of boron doping on the sensitivity to environmental embrittlement of Ni3Al-based alloys was investigated in this paper. The results show that the ductilizing effect of boron in Ni3Al is partly to suppress moisture-induced hydrogen embrittlement.The mechanism of this suppressing effect of boron relates to its severely decreasing the hydrogen diffusivity by boron segregated at the grain boundaries. The surface reaction of Fe3Al with water vapor and oxygen was experimentally confirmed by AES and XPS analysis. The kinetics of these reactions can be used to explain the different ductility behavior of aluminides in various environments.
文摘The anion kaolinite surface interactions and AuS - adsorption onto the surfaces of kaolinite were studied using the self consistent field discrete variation (SCF-X α-DV) method.Electronic structure and energies of the system of anion AuS - adsorbed on an atomic cluster of kaolinite were calculated.The results show that the systems with lower total energy are those AuS - adsorbed on the edge surfaces,which indicates that the systems of adsorption of AuS - on the edges are more stable relative to those adsorbed on the basal plane.On the other hand,bond order data suggest that significant shifting of atomic charge and the overlapping of electronic cloud between Au (Ⅰ) of the AuS - and the surface ions of kaolinite would take place in the systems with AuS - being adsorbed on the edges,especially at the site near Al octahedra.Therefore,it can be concluded that edge sites will dominate the complexation reactions of the surfaces of kaolinite,with negligible contributions from other functional groups on the basal plane,which are dominated by either siloxane sites in silica layers or aluminol sites in gibbsite layers.
基金by the opening project of State Key Laboratory of Polymer Materials Engineering(Sichuan University)(Nos.sklpme2019-4-38 and sklpme2019-4-36)L.X.is grateful to the National Natural Science Foundation of China(NSFC,No.22005205).
文摘In this work,we revisited the single-step synthesis of CdE(E=S,Se,and Te)quantum dots(QDs).Powdered CdO and elemental chalcogen were directly used for heating-up synthesis.Firstly,the in situ dissolution of the solid precursors and related QD formation channels were preliminarily investigated.In general,QDs were generated from homogeneous reactions between dissolved cadmium and chalcogen precursors in bulk solution.We found that,during single-step synthesis,both the dissolution of CdO and selenium proceeded faster than their ex situ dissolution respectively.To explain this result,we proposed the existence of extra surface reaction channels for QD formation.That is,QDs could also be generated via on-surface reactions between the solid precursors and the dissolved counter precursors(as“ligands”).The happening of these extra surface reactions would increase the overall dissolution rate of CdO and selenium.Further,the circulation of oleic acid which is peculiar to such single-step synthesis should also partly account for the accelerated dissolution of CdO.Finally,by comparing with two-step synthesis using pre-dissolved CdO,we presented that such single-step synthesis was reliable in making uniform CdE QDs with good reproducibility.Our work reaffirmed the great potential of this single-step strategy in cost-effective synthesis of monodisperse QDs.Moreover,the ligand-promoted surface reaction channels would be applicable in solution-phase synthesis of metal chalcogenide nanocrystals from solid precursors.
文摘Although photocatalytic water splitting has excellent potential for converting solar energy into chemical energy,the challenging charge separation process and sluggish surface catalytic reactions significantly limit progress in solar energy conversion using semiconductor photocatalysts.Herein,we demonstrate a feasible strategy involving the surface assembly of cobalt oxide species(CoO_(x))on a visible-light-responsive Cd_(0.9)Zn_(0.1)S(CZS)photocatalyst to fabricate a hierarchical CZS@CoO_(x) heterostructure.The unique hierarchical structure effectively accelerates the directional transfer of photogenerated charges,reducing charge recombination through the smooth interfacial heterojunction between CZS and CoO_(x),as evidenced by photoluminescence(PL)spectroscopy and various electrochemical characterizations.The surface cobalt species on the CZS material also act as efficient cocatalysts for photocatalytic hydrogen production,with activity even higher than that of noble metals.The well-defined CZS@CoO_(x) heterostructure not only enhances the interfacial separation of photoinduced charges,but also improves surface catalytic reactions.This leads to superior photocatalytic performances,with an apparent quantum efficiency of 20%at 420 nm for visible-light-driven hydrogen generation,which is one of the highest quantum efficiencies measured among noble-metal-free photocatalysts.Our work presents a potential pathway for controlling complex charge separation and catalytic reaction processes in photocatalysis,guiding the practical development of artificial photocatalysts for successful transformation of solar to chemical energy.
基金supported by the National Magnetic Confinement Fusion Science Program(2013GB110004,2014GB111000)
文摘Out-of-pile tritium release experiments were performed on Li4 Si O4 pebbles produced from lithium hydroxide under various compositions of sweep gas(He, 1.1% H2/He) and environmental moisture conditions. The experimental results indicate that tritium gas can be released directly from "dry" Li4 Si O4 under pure He gas. This phenomenon did not happen on "wet" samples, which means that the chemical form of released tritium is sensitive to moisture. Adding H2 to sweep gas may increase the overall desorption rate of tritium gas through H2 isotope exchange reaction, which occurs at a lower temperature than those of directly released tritium gas. Yet, the threshold of the H2 isotope exchange reaction is higher than the desorption reaction of tritiated water. Consequently, the effect of H2 isotope exchange reaction would reduce significantly on water adsorbed Li4 Si O4 samples.
基金supported by the National Natural Science Foundation of China under agreement number 22378026the Project of Construction of Innovative Teams and Teacher Career Development for Universities and Colleges under Beijing Municipality(IDHT20180508).
文摘The catalysis technology of propylene dimerization to form 4-methyl-1-pentene(4MP1)using a Cu-K/K_(2)CO_(3) solid base catalyst is a well-known heterogeneous catalytic reaction.In this study,the intrinsic kinetics of propylene dimerization were studied in a fixed-bed continuous reactor.Internal and external diffusion during the dimerization reaction experiments were eliminated by adjusting the flow rate of the carrier gas and the particle size of the catalyst support.Then,the concentration changes of each substance at the outlet of the catalyst bed under different residence times were investigated.Moreover,the suitable reaction kinetics equations was derived using the Langmuir Hinshelwood-Hougen-Watson kinetic model.Finally,the activation energy for each reaction involved in the dimerization reaction was calculated.The activation energies of 4MP1,branched by-products,and 1-hexene were 115.0,150.8,and 177.4 kJ/mol,respectively.The effect of process conditions on propylene dimerization with solid base catalysts was studied through kinetic model simulation.By comparing the theoretical values obtained from the simulation with the experimental results,the applicability and accuracy of the kinetic model were verified.
基金Projects(51305450,51275521)supported by the National Natural Science Foundation of China
文摘Removal of brittle materials in the brittle or ductile mode inevitably causes damaged or strained surface layers containing cracks, scratches or dislocations. Within elastic deformation, the arrangement of each atom can be recovered back to its original position without any defects introduced. Based on surface hydroxylation and chemisorption theory, material removal mechanism of quartz glass in the elastic mode is analyzed to obtain defect-free surface. Elastic contact condition between nanoparticle and quartz glass surface is confirmed from the Hertz contact theory model. Atoms on the quartz glass surface are removed by chemical bond generated by impact reaction in the elastic mode, so no defects are generated without mechanical process. Experiment was conducted on a numerically controlled system for nanoparticle jet polishing, and one flat quartz glass was polished in the elastic mode. Results show that scratches on the sample surface are completely removed away with no mechanical defects introduced, and microroughness(Ra) is decreased from 1.23 nm to 0.47 nm. Functional group Ce — O — Si on ceria nanoparticles after polishing was detected directly and indirectly by FTIR, XRD and XPS spectra analysis from which the chemical impact reaction is validated.
基金One of the authors(S.M.) was financially supported by UGC New Delhi,India through the Special Assistance Programme DSA Phase-1
文摘The aim of this article is to present the effects of transpiration on the unsteady two-dimensional boundary layer flow of non-Newtonian fluid passing through a stretching sheet in the presence of a first order constructive/destructive chemical reaction. The upper-convected Maxwell （UCM） model is used here to characterize the non-Newtonian behavior of the fluid. Using similarity solutions, the governing nonlinear partial differential equations are transformed into ordinary ones and are then solved numerically by the shooting method. The flow fields and mass transfer are significantly influenced by the governing parameters. The fluid velocity initially decreases as the unsteadiness parameter increases and the concentration decreases significantly due to the increase in the unsteadiness. The effect of increasing values of transpiration （suction） and the Maxwell parameter is to suppress the velocity field; however, the concentration is enhanced as transpiration （suction） and the Maxwell parameter increase. Also, it is found that the fluid velocity decreases as the magnetic parameter increases; however, the concentration increases in this case.
基金funding support from the Fundamental Research Funds for the Central Universities(Grant No.2023JBZY024)the National Natural Science Foundation of China(Grant Nos.52208382 and 52278387).
文摘To investigate the interaction of the bolt-reinforced rock and the surface support,an analytical model of the convergence-confinement type is proposed,considering the sequential installation of the fully grouted rockbolts and the surface support.The rock mass is assumed to be elastic-brittle-plastic material,obeying the linear Mohr-Coulomb criterion or the non-linear Hoek-Brown criterion.According to the strain states of the tunnel wall at bolt and surface support installation and the relative magnitude between the bolt length and the plastic depth during the whole process,six cases are categorized upon solving the problem.Each case is divided into three stages due to the different effects of the active rockbolts and the passive surface support.The fictitious pressure is introduced to quantify the threedimensional(3D)effect of the tunnel face,and thus,the actual physical location along the tunnel axis of the analytical section can be considered.By using the bolt-rock strain compatibility and the rocksurface support displacement compatibility conditions,the solutions of longitudinal tunnel displacement and the reaction pressure of surface support along the tunnel axis are obtained.The proposed analytical solutions are validated by a series of 3D numerical simulations.Extensive parametric studies are conducted to examine the effect of the typical parameters of rockbolts and surface support on the tunnel displacement and the reaction pressure of the surface support under different rock conditions.The results show that the rockbolts are more effective in controlling the tunnel displacement than the surface support,which should be installed as soon as possible with a suitable length.For tunnels excavated in weak rocks or with restricted displacement control requirements,the surface support should also be installed or closed timely with a certain stiffness.The proposed method provides a convenient alternative approach for the optimization of rockbolts and surface support at the preliminary stage of tunnel design.
基金the support from the National Key Research and Development Program(No.2018YFB1107500)Liao Ning Revitalization Talents Program(XLYC1907144)+1 种基金the National Natural Science Foundation of China(No.51503024)Dalian Youth Science and Technology Star Project Support Program(No.2017RQ104)。
文摘The electrochemical performance of hard carbon in sodium storage is still limited by its poor cycling stability and rate capability because of the sluggish kinetics process.In this study,we use a simple and effective method to accelerate the kinetics process by engineering the structure of the electrode to promote its surface and near-surface reactions.This goal is realized by the use of slightly aggregated ultra-small carbon spheres.The large specific surface area formed by the small spheres can provide abundant active sites for electrochemical reactions.The abundant mesopores and macropores derived from the secondary particle piled structure of the carbon spheres could facilitate the transport of electrolytes,shorten the diffusion distance of Na^(+)and accommodate the volume expansion during cycling.Benefiting from these unique structure features,PG700-3(carbon spheres with the diameters of 40-60 nm carbonized at 700℃)exhibits high performance for sodium storage.A high reversible capacity of 163 mAh g^(-1) could be delivered at a current density of 1.0 A g^(-1) after 100 cycles.Interestingly,at a current density of 10.0 A g^(-1),the specific capacity of PG700-3 gradually increases to 140 mAh g^(-1) after 10000 cycles,corresponding to a capacity retention of 112%.Given the enhanced kinetics of SIBs reactions,PG700-3 exhibits an excellent rate capability,i.e.,230 and 138 mAh g^(-1) at 0.1 and 5.0 A g^(-1),respectively.This study provides a facile method to attain high performance anode materials for SIBs.The design strategy and improvement mechanism could be extended to other materials for high rate applications.
基金supported by the National Natural Science Foundation of China(U21A20332,52103226,52202275,52203314,and 12204253)the Distinguished Young Scholars Fund of Jiangsu Province(BK20220061)the Fellowship of China Postdoctoral Science Foundation(2021 M702382)。
文摘As an alternative to conventional energy conversion and storage reactions,gas-involved electrochemical reactions,including the carbon dioxide reduction reaction(CO_(2)RR),nitrogen reduction reaction(NRR)and hydrogen evolution reaction(HER),have become an emerging research direction and have gained increasing attention due to their advantages of environmental friendliness and sustainability.Various studies have been designed to accelerate sluggish kinetics but with limited results.Most of them promote the reaction by modulating the intrinsic properties of the catalyst,ignoring the synergistic effect of the reaction as a whole.Due to the introduction of gas,traditional liquid-solid two-phase reactions are no longer applicable to future research.Since gas-involved electrochemical reactions mostly occur at the junctions of gaseous reactants,liquid electrolytes and solid catalysts,the focus of future research on reaction kinetics should gradually shift to three-phase reaction interfaces.In this review,we briefly introduce the formation and constraints of the three-phase interface and propose three criteria to judge its merit,namely,the active site,mass diffusion and electron mass transfer.Subsequently,a series of modulation methods and relevant works are discussed in detail from the three improvement directions of‘exposing more active sites,promoting mass diffusion and accelerating electron transfer’.Definitively,we provide farsighted insights into the understanding and research of three-phase interfaces in the future and point out the possible development direction of future regulatory methods,hoping that this review can broaden the future applications of the three-phase interface,including but not limited to gas-involved electrochemical reactions.
文摘The mechanism of the cycloaddition reaction between singlet dimethyl-silylene carbene and acetone has been investigated with density functional theory, From the potential energy profile, it can be predicted that the reaction has two competitive dominant reaction pathways. The presented rule of this reaction： the [2＋2] cycloaddition effect between the πorbital of dimethyl-silylene carbene and the π orbital of π-bonded compounds leads to the formation of a twisty four-membered ring intermediate and a planar four-membered ring product; The unsaturated property of C atom from carbene in the planar four-membered ring product,resulting in the generation of CH3-transfer product and silicic bis-heterocyclic compound.
文摘The intention of the current research is to address the conclusion of non-isothermal heterogeneous reaction on the stagnation-point flow of SWCNT-engine oil and MWCNT-engine oil nanofluid over a shrinking/stretching sheet.Further,exemplify the aspect of heat and mass transfer the upshot of magnetohydrodynamics(MHD),thermal radiation,and heat generation/absorption coefficient are exemplified.The bvp4 c from Matlab is pledged to acquire the numerical explanation of the problem that contains nonlinear system of ordinary differential equations(ODE).The impacts of miscellaneous important parameters on axial velocity,temperature field,concentration profile,skin friction coefficient,and local Nusselt number,are deliberated through graphical and numerically erected tabulated values.The solid volume fraction diminishes the velocity distribution while enhancing the temperature distribution.Further,the rate of shear stress declines with increasing the magnetic and stretching parameter for both SWCNT and MWCNT.
基金This work was supported by the National Natural Science Foundation of China （No.21506053） and Doctoral Scientific Research Foundation Project （KYY15023）.
文摘Developing a widely-used reactive force field is meaningful to explore the fundamental reaction mechanism on gas-surface chemical reaction dynamics due to its very high computational efficiency. We here present a study of hydrogen and its deuterated molecules dissociation on Pd surfaces based on a full-dimensional potential energy surface （PES） constructed by using a simple second moment approximation reactive force field （SMA RFF）. Although the descriptions of the adsorbate-substrate interaction contain only the dissociation reaction of H2/Pd（111） system, a good transferability of SMA potential energy surface （PES） is shown to investigate the hydrogen dissociation on Pd（100）. Our simulation results show that, the dissociation probabilities of H2 and its deuterated molecules on Pd（111） and Pd（100） surfaces keep non-monotonous variations with respect to the incident energy Ei, which is in good agreement with the previous ab initio molecular dynamics. Furthermore, for the oriented molecules, the dissociation probabilities of the oriented H2 （D2 and T2） molecule have the same orientation dependence behavior as those oriented HD （HT and DT） molecules.
