The development of efficient photocatalytic H2-evolution materials requires both rapid electron transfer and an effective interfacial catalysis reaction for H2 production. In addition to the well-known noble metals, l...The development of efficient photocatalytic H2-evolution materials requires both rapid electron transfer and an effective interfacial catalysis reaction for H2 production. In addition to the well-known noble metals, low-cost and earth-abundant non-noble metals can also act as electron- transfer mediators to modify photocatalysts. However, as almost all non-noble metals lack the interfacial catalytic active sites required for the H2-evolution reaction, the enhancement of the photocatalytic performance is limited. Therefore, the development of new interfacial active sites on metal-modified photocatalysts is of considerable importance. In this study, to enhance the photocatalytic evolution of H2 by Ni-modified TiO2, the formation of NiSx as interfacial active sites was promoted on the surface of Ni nanoparticles. Specifically, the co-modified TiO2/Ni-NiSx photocatalysts were prepared via a two-step process involving the photoinduced deposition of Ni on the TiO2 surface and the subsequent formation of NiSx on the Ni surface by a hydrothermal reaction method. It was found that the TiO2/Ni-NiSx photocatalysts exhibited enhanced photocatalytic H2-evolution activity. In particular, TiO2/Ni-NiSx(30%) showed the highest photocatalytic rate (223.74 μmol h.1), which was greater than those of TiO2, TiO2/Ni, and TiO2/NiSx by factors of 22.2, 8.0, and 2.2, respectively. The improved H2-evolution performance of TiO2/Ni-NiSx could be attributed to the excellent synergistic effect of Ni and NiSx, where Ni nanoparticles function as effective mediators to transfer electrons from the TiO2 surface and NiSx serves as interfacial active sites to capture H+ ions from solution and promote the interfacial H2-evolution reaction. The synergistic effect of the non-noble metal cocatalyst and the interfacial active sites may provide new insights for the design of highly efficient photocatalytic materials.展开更多
The combination of Pt^2＋, benzoquinone and NaNO2 forms an electron-transfer chain, which leads to the oxidation of methane by O2 in CF3COOH aqueous solution. The overall turnover number per hour （TOF） of methane at...The combination of Pt^2＋, benzoquinone and NaNO2 forms an electron-transfer chain, which leads to the oxidation of methane by O2 in CF3COOH aqueous solution. The overall turnover number per hour （TOF） of methane at 120 ℃ is 0.5 h^-1, however, only about one fourth （23%） of methane is converted to the desired product of methanol in the formation of CF3COOCH3. The over-oxidation of methane to CO2, over the catalyst with the Pt^2＋ species immobilized via 2,2＇-bipyridyl as a ligand on the silica substrate, is depressed distinctly. Under the same conditions, the conversion to methanol dominates, and no CO2 is observed, on account of the over-oxidation of methane, as confirmed by the isotope experiment.展开更多
Recently,transitionmetal sulfides have attractedmuch attention due to their better catalytic capacities as peroxymonosulfate(PMS)activator than their metal oxide counterparts.However,the systematic studies on PMS acti...Recently,transitionmetal sulfides have attractedmuch attention due to their better catalytic capacities as peroxymonosulfate(PMS)activator than their metal oxide counterparts.However,the systematic studies on PMS activation using transition metal sulfides are still lacking.In this work,manganese sulfide(MnS)materials were synthesized via a MOFs-derived method and utilized for PMS activation to degrade levofloxacin(LVF)in water for the first time.As expected,MnS exhibited remarkable LVF degradation efficiency by PMS activation,whichwas distinctly higher than Mn_(2)O_(3).The results of quenching experiments,electro spin resonance identification and electrochemical tests indicated that electron-transfer progress was the dominant mechanism inα-MnS/PMS system.Meanwhile,the presence of ^(1)O_(2) and radicals further became the removal of LVF byα-MnS/PMS system into a radical/nonradical coupling process.The superior electrical conductivity ofα-MnS thanα-Mn_(2)O_(3) was revealed by DFT calculations,which resulted in the higher catalytic capacity ofα-MnS.The result of XPS also indicated the S species in MnS accelerated the recycle of Mn(IV)/Mn(II)and then promoted the generation of radicals.Furthermore,the influence of various environmental conditions on LVF removal and the reusability ofα-MnS were also investigated,which demonstrated the high application potential ofα-MnS/PMS system.Finally,six possible pathways of LVF oxidation in the system were proposed based on the identified byproducts and their ecotoxicity was evaluated with ECOSAR method.This work promotes the fundamental understanding of PMS activation byα-MnS and provides useful information for practical application of manganese sulfide in water treatment.展开更多
The diffusion coefficients(Dapp) and the heterogeneous electron transfer rate constants(ks)for ferrocene in several polymer solvents were determined by using steady-stae voltammetry. Thetemperature dependence of the t...The diffusion coefficients(Dapp) and the heterogeneous electron transfer rate constants(ks)for ferrocene in several polymer solvents were determined by using steady-stae voltammetry. Thetemperature dependence of the two parameters indicates Arrhenius behavior. The polymer solventeffects on diffusion and electron transfer dynamics of ferrocene were discussed展开更多
Abstract: : The substituted nitroarenes were reduced effectively to the corresponding aniline deriva tives by an insoluble resin with viologen structure as an electron-transfer catalyst(ETC) in dichloromethane-resin...Abstract: : The substituted nitroarenes were reduced effectively to the corresponding aniline deriva tives by an insoluble resin with viologen structure as an electron-transfer catalyst(ETC) in dichloromethane-resin-water -three-phase system.展开更多
This paper studies the intramolecular photoinduced electron-transfer （PET） of covalent bonded azobenzene-perylene diimide （AZO-PDI） in solvents by using steady-state and time-resolved fluorescence spectroscopy tog...This paper studies the intramolecular photoinduced electron-transfer （PET） of covalent bonded azobenzene-perylene diimide （AZO-PDI） in solvents by using steady-state and time-resolved fluorescence spectroscopy together with ultrafast transient absorption spectroscopic techniques. Fast fluorescence quenching is observed when AZO-PDI is excited at characteristic wavelengths of AZO and perylene moieties. Reductive electron-transfer with transfer rate faster than 10^11 s^-1 is found. This PET process is also consolidated by femtosecond transient absorption spectra.展开更多
A spectrophotometric investigation of oxidation of chondroitin-4-sulfate(CS)as a sustainable and biodegradable sulfated macromolecule by oxyanion permanganate ion as multi-equivalent oxidant in acid perchlorate soluti...A spectrophotometric investigation of oxidation of chondroitin-4-sulfate(CS)as a sustainable and biodegradable sulfated macromolecule by oxyanion permanganate ion as multi-equivalent oxidant in acid perchlorate solutions at a constant ionic strength of 2.0 mol dm^(-3)has been studied.The experimental results on the influence of the concentration of the reactants the reaction rates revealed first-order dependence in MnO^(-)_(4),fractional second-order in[CS]and fractional first-order with respect to the hydrogen ion concentration.The hydrogen acid concentration dependence of the rate constants indicated that the oxidation rates were increased with increasing the acid concentration which means that the oxidation reaction is of acid-catalyzed nature.The oxidation of all other polysaccharides by this oxidant in acidic solutions indicated that the oxidation processes were proceeding throughout two distinct stages.The first stage was relatively slow,followed by a more fast reaction in the second stage.The addition of Mn^(2+)and F^(-)ions to the reaction mixtures indicated that the Mn^(3+)and/or Mn^(4+)as the reduced forms of permanganate were the reactive species in the second fast stage.Here,neither formation of Mn^(3+)and/or Mn^(4+)transient species nor presence of two stages in the oxidation reaction were detected in the oxidation process,and this result was found to be on contrary to that observed for oxidation of all other polysaccharides by this oxidant.Formation of 1:2 coordination biopolymer intermediate complexes prior to the rate-determining step was revealed,kinetically.Identification of the oxidation product revealed the formation of keto-acid as derivative precursor of CS oxidation.This product was identified by formation of 2,4-dinitrophenyhydrazone and dioxime as wells as by the bands at frequencies 3430(OH of COOH group);1760-1730 cm^(-1)(broad)for C=O of diketone;1639 cm^(-1)ofν_(as),OCO;1418 cm^(-1)ofν_(s)OCO and 1338 cm^(-1)of C-O-C,respectively,in the FTIR spectra.Two-electron transfer process of inner-sphere nature in the slowest step has been suggested.A tentative reaction mechanism in terms of the kinetic parameters have been suggested and discussed.展开更多
Based on the capture force field potential model and the adiabatic invariant proposed by Bates, adopting improved average dipole orientation (IADO) theory, the force constants between transition metal ions and benzene...Based on the capture force field potential model and the adiabatic invariant proposed by Bates, adopting improved average dipole orientation (IADO) theory, the force constants between transition metal ions and benzene (bz) and also a series of inner-sphere reoganization energy (REin) were calculated. The reasons for the differences between theoretical predictions and experimental results were discussed.展开更多
The active intermediate'carbon radical' was detected by the spin—trapping reagent (POBN) during the debromination of Ph_2CHBr in the presence of viologen derivatives as electron—transfer catalysts(ETC).
The diffusion coefficients(Dapp) and the heterogeneous electron-transfer rate constants(ks)for ferrocene and its seven derivatives in MPEG/LiClO4 electrolyte were determined by using steadystate voltammetry. The two p...The diffusion coefficients(Dapp) and the heterogeneous electron-transfer rate constants(ks)for ferrocene and its seven derivatives in MPEG/LiClO4 electrolyte were determined by using steadystate voltammetry. The two parameters increase with increasing temperature, indicating Arrhenius behavior. The effects of the nature of electroactive solute molecules on Dapp, ks, and the half-wave potentials(E1/2) are discussed.展开更多
The ditheion coefficients(Dapp) and the heterogeneous electron-transfer rate constan(ks)for ferrocene in MPEG/salt electrolytes were determined by using Steady-stae voltammetry. The temperature dependence of the two p...The ditheion coefficients(Dapp) and the heterogeneous electron-transfer rate constan(ks)for ferrocene in MPEG/salt electrolytes were determined by using Steady-stae voltammetry. The temperature dependence of the two parameters obeys the Arrhenius equstion. The effect of the ionic size of sir supporting electrolytes on diffusion and electron transfer dynamics of fermcene was discussed展开更多
Maximizing ultrafast electron-transfer kinetics in semiconductor is pivotal but challenging for highefficiency solar-to-energy during the photocatalytic reaction process due to the intrinsic property of photocatalysts...Maximizing ultrafast electron-transfer kinetics in semiconductor is pivotal but challenging for highefficiency solar-to-energy during the photocatalytic reaction process due to the intrinsic property of photocatalysts with low surface electron density.Herein,a model photocatalyst CdS@Mo is synthesized through a typical hydrothermal method for modulating the ultrafast electron-transfer to enhance the surface electron density.X-ray absorption fine spectra(XAFS)reveal that Mo is coordinated with S atoms to form a Mo-S_(6) configuration which is different from common MoS_(2) and Mo foil structures.Based on the femtosecond transient absorption spectra(fs-TAS),it is found that the formation of Mo-S6 configuration contributes to the fast decay of CdS signal and Mo-S_(6) signal reactivation,illustrating the ultrafast electron-transfer(∼2.2 ps)from CdS to Mo-S_(6) configuration,which achieves the enhanced electron density of photocatalyst surface.Finally,a holistic photocatalytic performance evaluation discloses that the growing of Mo-S_(6) configuration obviously improves the photocatalytic hydrogen evolution(PHE)effi-ciency of CdS from 28.5 to 47.5 mmol g^(-1)h^(-1)with a solar-to-hydrogen(STH)efficiency of 0.10%which is seldomly discussed in the system containing sacrificial agents.This work opens a new path to modulate the surface electron density by tuning the ultrafast electron-transfer for enhancing reaction efficiency in electron-density-dependent systems.展开更多
The potential energy surface and reaction mechanism corresponding to the reaction of ytterbium monocation with fluoromethane, which represents a prototype of the activation of C-F bond in fluorohydrocarbons by bare la...The potential energy surface and reaction mechanism corresponding to the reaction of ytterbium monocation with fluoromethane, which represents a prototype of the activation of C-F bond in fluorohydrocarbons by bare lanthanide cations, have been investigated for the first time by using density functional theory. A direct fluorine abstraction mechanism was revealed, and the related thermochemistry data were determined. The electron-transfer reactivity of the reaction was analyzed using the two-state model, and a strongly avoided crossing behavior on the transition state region was shown. The present results support the reaction mechanism inferred from early experimental data and the related thermochemistry data can provide a guide for further experimental researches.展开更多
The investigation of charge carrier kinetics has long been a cornerstone of polymer photocatalysis research.However,the role of proton transport behavior in photocatalytic processes has often been underappreciated,des...The investigation of charge carrier kinetics has long been a cornerstone of polymer photocatalysis research.However,the role of proton transport behavior in photocatalytic processes has often been underappreciated,despite its fundamental importance in proton-coupled electron-transfer reactions.Addressing this gap,we present a novel BF_(2)-bridged covalent organic framework(C2-COF-BF2) that undergoes post-synthetic modification with boron trifluoride,designed to confer a dual functional advantage.Specifically,the incorporated BF_(2) moieties are engineered to induce a donor-acceptor effect and potentially serve as continuous supply sites for activated protons.This bifunctional role not only enhances charge separation and migration while suppressing electron-hole recombination but also facilitates proton transport,thereby enabling improved performance in both photocatalytic hydrogen evolution reaction(HER) and H_(2) O_(2) production.Remarkably,the photocatalytic HER performance of C2-COF-BF2(AQY_(450 nm)= 8.78%) ranks among the highest efficiencies reported for COF-based photocatalysts to date.These findings highlight an innovative pathway for advancing the rational design of COF photocatalysts,offering a synergistic optimization of charge carrier kinetics and mass transfer processes to achieve unprecedented photocatalytic efficiency.展开更多
Hydrogen is one of the most promising energy carriers to replace fossil fuels and electrolyzing water to produce hydrogen is a very effective method.However,designing highly active and stable non-precious metal hydrog...Hydrogen is one of the most promising energy carriers to replace fossil fuels and electrolyzing water to produce hydrogen is a very effective method.However,designing highly active and stable non-precious metal hydrogen evolution electrocatalysts that can be used in universal pH is a huge challenge.Here,we have reported a simple strategy to develop a highly active and durable non-precious MoO2-Ni electrocatalyst for hydrogen evolution reaction(HER)in a wide pH range.The MoO2-Ni catalyst exhibits a superior electrocatalytic performance with low overpotentials of 46,69,and 84 mV to reach-10 mA cm-2 in 1.0 M KOH,0.5 M H2SO4,and 1.0 M PBS electrolytes,respectively.At the same time,the catalyst also shows outstanding stability over a wide pH range.It is particularly noted that the catalytic performance of MoO2-Ni in alkaline solution is comparable to the highest performing catalysts reported.The outstanding HER performance is mainly attributed to the collective effect of the rational morphological design,electronic structure engineering,and strong interfacial coupling between MoO2 and Ni in heterojunctions.This work provides a viable method for the synthesis of inexpensive and efficient HER electrocatalysts for the use in wide pH ranges.展开更多
The electron-transfer (ET) reaction between Fe(CN)64- and copper zinc superoxide dismutase (CuZn-SOD) occurs at the active site of the enzyme. The ET parameters which are sensitive to the denaturation have been used t...The electron-transfer (ET) reaction between Fe(CN)64- and copper zinc superoxide dismutase (CuZn-SOD) occurs at the active site of the enzyme. The ET parameters which are sensitive to the denaturation have been used to determine the conformational changes of the active site induced by guanidine hydrochloride and thermal denaturation. The decreases of ET rates for all the denatured enzyme samples reflect the collapse of the active cavity of enzyme in the unfolding processes. The interesting changes of ET amplitude for the enzyme denatured at different pH values suggest that electrostatic interaction plays an important role in the conformational changes of active site. From the results of the kinetic analyses, it is concluded that the conformational changes of the active site are parallel with the inactivation.展开更多
Alkali metal fullerides (A<sub>n</sub>C<sub>60</sub>) are versatile reagents in synthetic chemistry ofbuckminsterfullerene, for example, controlled chemical functionalizations of buckminster-fu...Alkali metal fullerides (A<sub>n</sub>C<sub>60</sub>) are versatile reagents in synthetic chemistry ofbuckminsterfullerene, for example, controlled chemical functionalizations of buckminster-fullerene might be achieved by using precursors C<sub>60</sub><sup>n-</sup>M in a desired oxidation state.Vapor-transport technique was widely used to investigate the electron-transfer reactionsbetween C<sub>60</sub> and alkali metal. This method, however, required higher temperature condi-tions （200—400℃） and a longer period of reaction time （10—15 d）. Direct reactions of C<sub>60</sub>展开更多
A number of electron donors, acceptors and diads containing xanthene dyes were sythesized. When the dyes were excited, the rate constants and the efficiencies of the intermolecular and intramolecular photo-induced ele...A number of electron donors, acceptors and diads containing xanthene dyes were sythesized. When the dyes were excited, the rate constants and the efficiencies of the intermolecular and intramolecular photo-induced electron transfer reactions were determined and calculated. It is found that the photo-induced electron transfer reactions occurred between xanthene dyes and many, including very weak donors or acceptors. The rate constants of intermolecular reactions were controlled by diffusion, and influenced by the reactant concentrations. The laser flash experiments showed that for low reactant concentrations, this kind of reactions took place mainly via the triplet excited state of the dyes. If different electric charges exist with dyes and donors/acceptors, there will be static quenching of the dyes’ fluorescence. The intramolecular electron transfer reactions are independent of the solution concentrations, and they may directly proceed via the singlet excited state of the dyes effectively.展开更多
Electron-transfer processes facilitated by hydrophobic-lipophilic interaction (HLI) between excited N-alkylcarbazoles (1-n, n = 4, 8, 12, 16) as electron donors and 2,4-dinitrophenyl carboxylates (2-n, n = 4, 8, 12, 1...Electron-transfer processes facilitated by hydrophobic-lipophilic interaction (HLI) between excited N-alkylcarbazoles (1-n, n = 4, 8, 12, 16) as electron donors and 2,4-dinitrophenyl carboxylates (2-n, n = 4, 8, 12, 16) or pentafluorophenyl carboxylates (3-n, n = 4, 8, 12, 16) as electron acceptors have been investigated by means of fluorescence spectroscopy in aqueous or aquiorgano binary mixtures. The fluorescence quenching of -n* by 2-n or - n indicates that preassociation precedes the electron transfer. The extent of HLI-driven coaggregation of the acceptor and the donor may be assessed from the B value of the equation I0/I = A + B [Q]. The chain-length effect and possibly also a chain-fold-ability effect, as well as the solvent aggregating power (SAgP) effect have been observed. Comparison of roe quenching constants (B) for 1-n*/2-n combinations and 1-n*/ 3-n combinations shows that the order of increasing B values for the quenching processes is 3-n < 2-n.展开更多
基金supported by the National Natural Science Foundation of China(21477094)the Fundamental Research Funds for the Central Universities(WUT 2017IB002)~~
文摘The development of efficient photocatalytic H2-evolution materials requires both rapid electron transfer and an effective interfacial catalysis reaction for H2 production. In addition to the well-known noble metals, low-cost and earth-abundant non-noble metals can also act as electron- transfer mediators to modify photocatalysts. However, as almost all non-noble metals lack the interfacial catalytic active sites required for the H2-evolution reaction, the enhancement of the photocatalytic performance is limited. Therefore, the development of new interfacial active sites on metal-modified photocatalysts is of considerable importance. In this study, to enhance the photocatalytic evolution of H2 by Ni-modified TiO2, the formation of NiSx as interfacial active sites was promoted on the surface of Ni nanoparticles. Specifically, the co-modified TiO2/Ni-NiSx photocatalysts were prepared via a two-step process involving the photoinduced deposition of Ni on the TiO2 surface and the subsequent formation of NiSx on the Ni surface by a hydrothermal reaction method. It was found that the TiO2/Ni-NiSx photocatalysts exhibited enhanced photocatalytic H2-evolution activity. In particular, TiO2/Ni-NiSx(30%) showed the highest photocatalytic rate (223.74 μmol h.1), which was greater than those of TiO2, TiO2/Ni, and TiO2/NiSx by factors of 22.2, 8.0, and 2.2, respectively. The improved H2-evolution performance of TiO2/Ni-NiSx could be attributed to the excellent synergistic effect of Ni and NiSx, where Ni nanoparticles function as effective mediators to transfer electrons from the TiO2 surface and NiSx serves as interfacial active sites to capture H+ ions from solution and promote the interfacial H2-evolution reaction. The synergistic effect of the non-noble metal cocatalyst and the interfacial active sites may provide new insights for the design of highly efficient photocatalytic materials.
基金Ministry of Science and Technology of China (2005CB221405)
文摘The combination of Pt^2＋, benzoquinone and NaNO2 forms an electron-transfer chain, which leads to the oxidation of methane by O2 in CF3COOH aqueous solution. The overall turnover number per hour （TOF） of methane at 120 ℃ is 0.5 h^-1, however, only about one fourth （23%） of methane is converted to the desired product of methanol in the formation of CF3COOCH3. The over-oxidation of methane to CO2, over the catalyst with the Pt^2＋ species immobilized via 2,2＇-bipyridyl as a ligand on the silica substrate, is depressed distinctly. Under the same conditions, the conversion to methanol dominates, and no CO2 is observed, on account of the over-oxidation of methane, as confirmed by the isotope experiment.
基金supported by the Natural Science Foundation of Shanghai(No.17ZR1407000)the National Natural Science Foundation of China(No.41201302)the Fundamental Research Funds for the Central Universities(No.222201514337).
文摘Recently,transitionmetal sulfides have attractedmuch attention due to their better catalytic capacities as peroxymonosulfate(PMS)activator than their metal oxide counterparts.However,the systematic studies on PMS activation using transition metal sulfides are still lacking.In this work,manganese sulfide(MnS)materials were synthesized via a MOFs-derived method and utilized for PMS activation to degrade levofloxacin(LVF)in water for the first time.As expected,MnS exhibited remarkable LVF degradation efficiency by PMS activation,whichwas distinctly higher than Mn_(2)O_(3).The results of quenching experiments,electro spin resonance identification and electrochemical tests indicated that electron-transfer progress was the dominant mechanism inα-MnS/PMS system.Meanwhile,the presence of ^(1)O_(2) and radicals further became the removal of LVF byα-MnS/PMS system into a radical/nonradical coupling process.The superior electrical conductivity ofα-MnS thanα-Mn_(2)O_(3) was revealed by DFT calculations,which resulted in the higher catalytic capacity ofα-MnS.The result of XPS also indicated the S species in MnS accelerated the recycle of Mn(IV)/Mn(II)and then promoted the generation of radicals.Furthermore,the influence of various environmental conditions on LVF removal and the reusability ofα-MnS were also investigated,which demonstrated the high application potential ofα-MnS/PMS system.Finally,six possible pathways of LVF oxidation in the system were proposed based on the identified byproducts and their ecotoxicity was evaluated with ECOSAR method.This work promotes the fundamental understanding of PMS activation byα-MnS and provides useful information for practical application of manganese sulfide in water treatment.
文摘The diffusion coefficients(Dapp) and the heterogeneous electron transfer rate constants(ks)for ferrocene in several polymer solvents were determined by using steady-stae voltammetry. Thetemperature dependence of the two parameters indicates Arrhenius behavior. The polymer solventeffects on diffusion and electron transfer dynamics of ferrocene were discussed
文摘Abstract: : The substituted nitroarenes were reduced effectively to the corresponding aniline deriva tives by an insoluble resin with viologen structure as an electron-transfer catalyst(ETC) in dichloromethane-resin-water -three-phase system.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 10504001,60878019,10821062,10934001,60677002 and 10828407)the National Basic Research Program of China (Grant Nos. 2009CB930504,2007CB307001,2006CB921601 and 2006CB806007)
文摘This paper studies the intramolecular photoinduced electron-transfer （PET） of covalent bonded azobenzene-perylene diimide （AZO-PDI） in solvents by using steady-state and time-resolved fluorescence spectroscopy together with ultrafast transient absorption spectroscopic techniques. Fast fluorescence quenching is observed when AZO-PDI is excited at characteristic wavelengths of AZO and perylene moieties. Reductive electron-transfer with transfer rate faster than 10^11 s^-1 is found. This PET process is also consolidated by femtosecond transient absorption spectra.
基金supported by the Department of Chemistry,Faculty of Science,Assiut University,Assiut,71516,Assiut,Egypt.
文摘A spectrophotometric investigation of oxidation of chondroitin-4-sulfate(CS)as a sustainable and biodegradable sulfated macromolecule by oxyanion permanganate ion as multi-equivalent oxidant in acid perchlorate solutions at a constant ionic strength of 2.0 mol dm^(-3)has been studied.The experimental results on the influence of the concentration of the reactants the reaction rates revealed first-order dependence in MnO^(-)_(4),fractional second-order in[CS]and fractional first-order with respect to the hydrogen ion concentration.The hydrogen acid concentration dependence of the rate constants indicated that the oxidation rates were increased with increasing the acid concentration which means that the oxidation reaction is of acid-catalyzed nature.The oxidation of all other polysaccharides by this oxidant in acidic solutions indicated that the oxidation processes were proceeding throughout two distinct stages.The first stage was relatively slow,followed by a more fast reaction in the second stage.The addition of Mn^(2+)and F^(-)ions to the reaction mixtures indicated that the Mn^(3+)and/or Mn^(4+)as the reduced forms of permanganate were the reactive species in the second fast stage.Here,neither formation of Mn^(3+)and/or Mn^(4+)transient species nor presence of two stages in the oxidation reaction were detected in the oxidation process,and this result was found to be on contrary to that observed for oxidation of all other polysaccharides by this oxidant.Formation of 1:2 coordination biopolymer intermediate complexes prior to the rate-determining step was revealed,kinetically.Identification of the oxidation product revealed the formation of keto-acid as derivative precursor of CS oxidation.This product was identified by formation of 2,4-dinitrophenyhydrazone and dioxime as wells as by the bands at frequencies 3430(OH of COOH group);1760-1730 cm^(-1)(broad)for C=O of diketone;1639 cm^(-1)ofν_(as),OCO;1418 cm^(-1)ofν_(s)OCO and 1338 cm^(-1)of C-O-C,respectively,in the FTIR spectra.Two-electron transfer process of inner-sphere nature in the slowest step has been suggested.A tentative reaction mechanism in terms of the kinetic parameters have been suggested and discussed.
文摘Based on the capture force field potential model and the adiabatic invariant proposed by Bates, adopting improved average dipole orientation (IADO) theory, the force constants between transition metal ions and benzene (bz) and also a series of inner-sphere reoganization energy (REin) were calculated. The reasons for the differences between theoretical predictions and experimental results were discussed.
文摘The active intermediate'carbon radical' was detected by the spin—trapping reagent (POBN) during the debromination of Ph_2CHBr in the presence of viologen derivatives as electron—transfer catalysts(ETC).
文摘The diffusion coefficients(Dapp) and the heterogeneous electron-transfer rate constants(ks)for ferrocene and its seven derivatives in MPEG/LiClO4 electrolyte were determined by using steadystate voltammetry. The two parameters increase with increasing temperature, indicating Arrhenius behavior. The effects of the nature of electroactive solute molecules on Dapp, ks, and the half-wave potentials(E1/2) are discussed.
文摘The ditheion coefficients(Dapp) and the heterogeneous electron-transfer rate constan(ks)for ferrocene in MPEG/salt electrolytes were determined by using Steady-stae voltammetry. The temperature dependence of the two parameters obeys the Arrhenius equstion. The effect of the ionic size of sir supporting electrolytes on diffusion and electron transfer dynamics of fermcene was discussed
基金The National Natural Science Foundation of China(Nos.22178291,22209135,22002123,and 22311530118)the National Science Fund for the Distinguished Young Scholars(No.52325401)。
文摘Maximizing ultrafast electron-transfer kinetics in semiconductor is pivotal but challenging for highefficiency solar-to-energy during the photocatalytic reaction process due to the intrinsic property of photocatalysts with low surface electron density.Herein,a model photocatalyst CdS@Mo is synthesized through a typical hydrothermal method for modulating the ultrafast electron-transfer to enhance the surface electron density.X-ray absorption fine spectra(XAFS)reveal that Mo is coordinated with S atoms to form a Mo-S_(6) configuration which is different from common MoS_(2) and Mo foil structures.Based on the femtosecond transient absorption spectra(fs-TAS),it is found that the formation of Mo-S6 configuration contributes to the fast decay of CdS signal and Mo-S_(6) signal reactivation,illustrating the ultrafast electron-transfer(∼2.2 ps)from CdS to Mo-S_(6) configuration,which achieves the enhanced electron density of photocatalyst surface.Finally,a holistic photocatalytic performance evaluation discloses that the growing of Mo-S_(6) configuration obviously improves the photocatalytic hydrogen evolution(PHE)effi-ciency of CdS from 28.5 to 47.5 mmol g^(-1)h^(-1)with a solar-to-hydrogen(STH)efficiency of 0.10%which is seldomly discussed in the system containing sacrificial agents.This work opens a new path to modulate the surface electron density by tuning the ultrafast electron-transfer for enhancing reaction efficiency in electron-density-dependent systems.
基金supported by the National Science Foundation of Shandong Province(No.Z2000B02).
文摘The potential energy surface and reaction mechanism corresponding to the reaction of ytterbium monocation with fluoromethane, which represents a prototype of the activation of C-F bond in fluorohydrocarbons by bare lanthanide cations, have been investigated for the first time by using density functional theory. A direct fluorine abstraction mechanism was revealed, and the related thermochemistry data were determined. The electron-transfer reactivity of the reaction was analyzed using the two-state model, and a strongly avoided crossing behavior on the transition state region was shown. The present results support the reaction mechanism inferred from early experimental data and the related thermochemistry data can provide a guide for further experimental researches.
基金supported by the National Natural Science Foundation of China (21972021,22271281,22325109,22171263,62227815,91961115,22494633,22422508)the Natural Science Foundation of Fujian Province (2024J01238,2022J06032,2021J02017)+5 种基金the Scientific Research and Equipment Development Project of Chinese Academy of Sciences (YJKYQ20210024)the Fujian Science&Technology Innovation Laboratory for Optoelectronic Information of China (2021ZR101)the Self-deployment Project Research Program of Haixi Institutes,Chinese Academy of Sciences (CXZX-2022-GH09,CXZX-2023-GS03,CXZX-2022-JQ03)the Key Research Project of Chinese Academy of Sciences(KGFZD-145-25-21)the Strategic Priority Research Program of Chinese Academy of Sciences (XDB1170000)the 111 Project (D16008)。
文摘The investigation of charge carrier kinetics has long been a cornerstone of polymer photocatalysis research.However,the role of proton transport behavior in photocatalytic processes has often been underappreciated,despite its fundamental importance in proton-coupled electron-transfer reactions.Addressing this gap,we present a novel BF_(2)-bridged covalent organic framework(C2-COF-BF2) that undergoes post-synthetic modification with boron trifluoride,designed to confer a dual functional advantage.Specifically,the incorporated BF_(2) moieties are engineered to induce a donor-acceptor effect and potentially serve as continuous supply sites for activated protons.This bifunctional role not only enhances charge separation and migration while suppressing electron-hole recombination but also facilitates proton transport,thereby enabling improved performance in both photocatalytic hydrogen evolution reaction(HER) and H_(2) O_(2) production.Remarkably,the photocatalytic HER performance of C2-COF-BF2(AQY_(450 nm)= 8.78%) ranks among the highest efficiencies reported for COF-based photocatalysts to date.These findings highlight an innovative pathway for advancing the rational design of COF photocatalysts,offering a synergistic optimization of charge carrier kinetics and mass transfer processes to achieve unprecedented photocatalytic efficiency.
基金supported by the National Natural Science Foundation of China(21965005)Natural Science Foundation of Guangxi Province(2018GXNSFAA294077 and 2018GXNSFAA281220)Project of High-Level Talents of Guangxi(F-KA18015 and 2018ZD004)。
文摘Hydrogen is one of the most promising energy carriers to replace fossil fuels and electrolyzing water to produce hydrogen is a very effective method.However,designing highly active and stable non-precious metal hydrogen evolution electrocatalysts that can be used in universal pH is a huge challenge.Here,we have reported a simple strategy to develop a highly active and durable non-precious MoO2-Ni electrocatalyst for hydrogen evolution reaction(HER)in a wide pH range.The MoO2-Ni catalyst exhibits a superior electrocatalytic performance with low overpotentials of 46,69,and 84 mV to reach-10 mA cm-2 in 1.0 M KOH,0.5 M H2SO4,and 1.0 M PBS electrolytes,respectively.At the same time,the catalyst also shows outstanding stability over a wide pH range.It is particularly noted that the catalytic performance of MoO2-Ni in alkaline solution is comparable to the highest performing catalysts reported.The outstanding HER performance is mainly attributed to the collective effect of the rational morphological design,electronic structure engineering,and strong interfacial coupling between MoO2 and Ni in heterojunctions.This work provides a viable method for the synthesis of inexpensive and efficient HER electrocatalysts for the use in wide pH ranges.
基金Project supported by China Postdoctoral Science Foundation and the National Natural Science Foundation of China.Abbteviation: CuZn-SOD,copper zinc superoxide dismutase ET, electron-transfer+1 种基金GuHCl,guanidine hydrochlorideMES, 2-morpholinoethane sulfonic
文摘The electron-transfer (ET) reaction between Fe(CN)64- and copper zinc superoxide dismutase (CuZn-SOD) occurs at the active site of the enzyme. The ET parameters which are sensitive to the denaturation have been used to determine the conformational changes of the active site induced by guanidine hydrochloride and thermal denaturation. The decreases of ET rates for all the denatured enzyme samples reflect the collapse of the active cavity of enzyme in the unfolding processes. The interesting changes of ET amplitude for the enzyme denatured at different pH values suggest that electrostatic interaction plays an important role in the conformational changes of active site. From the results of the kinetic analyses, it is concluded that the conformational changes of the active site are parallel with the inactivation.
基金Project supported by the National Natural Science Foundation of China and Science Foundation of Shanghai Committee of Science and Technology.
文摘Alkali metal fullerides (A<sub>n</sub>C<sub>60</sub>) are versatile reagents in synthetic chemistry ofbuckminsterfullerene, for example, controlled chemical functionalizations of buckminster-fullerene might be achieved by using precursors C<sub>60</sub><sup>n-</sup>M in a desired oxidation state.Vapor-transport technique was widely used to investigate the electron-transfer reactionsbetween C<sub>60</sub> and alkali metal. This method, however, required higher temperature condi-tions （200—400℃） and a longer period of reaction time （10—15 d）. Direct reactions of C<sub>60</sub>
文摘A number of electron donors, acceptors and diads containing xanthene dyes were sythesized. When the dyes were excited, the rate constants and the efficiencies of the intermolecular and intramolecular photo-induced electron transfer reactions were determined and calculated. It is found that the photo-induced electron transfer reactions occurred between xanthene dyes and many, including very weak donors or acceptors. The rate constants of intermolecular reactions were controlled by diffusion, and influenced by the reactant concentrations. The laser flash experiments showed that for low reactant concentrations, this kind of reactions took place mainly via the triplet excited state of the dyes. If different electric charges exist with dyes and donors/acceptors, there will be static quenching of the dyes’ fluorescence. The intramolecular electron transfer reactions are independent of the solution concentrations, and they may directly proceed via the singlet excited state of the dyes effectively.
文摘Electron-transfer processes facilitated by hydrophobic-lipophilic interaction (HLI) between excited N-alkylcarbazoles (1-n, n = 4, 8, 12, 16) as electron donors and 2,4-dinitrophenyl carboxylates (2-n, n = 4, 8, 12, 16) or pentafluorophenyl carboxylates (3-n, n = 4, 8, 12, 16) as electron acceptors have been investigated by means of fluorescence spectroscopy in aqueous or aquiorgano binary mixtures. The fluorescence quenching of -n* by 2-n or - n indicates that preassociation precedes the electron transfer. The extent of HLI-driven coaggregation of the acceptor and the donor may be assessed from the B value of the equation I0/I = A + B [Q]. The chain-length effect and possibly also a chain-fold-ability effect, as well as the solvent aggregating power (SAgP) effect have been observed. Comparison of roe quenching constants (B) for 1-n*/2-n combinations and 1-n*/ 3-n combinations shows that the order of increasing B values for the quenching processes is 3-n < 2-n.
