Hydrogen peroxide(H_(2)O_(2))has gained widespread attention as a versatile oxidant and a mild disin-fectant.Here,an electrostatic self-assembly method is applied to couple ZnSe quantum dots(QDs)with a flower-like cov...Hydrogen peroxide(H_(2)O_(2))has gained widespread attention as a versatile oxidant and a mild disin-fectant.Here,an electrostatic self-assembly method is applied to couple ZnSe quantum dots(QDs)with a flower-like covalent organic framework(COF)to form a step-scheme(S-scheme)photocata-lyst for H_(2)O_(2)production.The as-prepared S-scheme photocatalyst exhibits a broad light absorption range with an edge at 810 nm owing to the synergistic effect between the ZnSe QDs and COF.The S-scheme charge-carrier transfer mechanism is validated by performing Fermi level calculations and in-situ X-ray photoelectron and femtosecond transient absorption spectroscopies.Photolumi-nescence,time-resolved photoluminescence,photocurrent response,electrochemical impedance spectroscopy,and electron paramagnetic resonance results show that the S-scheme heterojunction not only promotes charge carrier separation but also boosts the redox ability,resulting in enhanced photocatalytic performance.Remarkably,a 10%-ZnSe QD/COF has excellent photocatalytic H_(2)O_(2)-production activity,and the optimal S-scheme composite with ethanol as the hole scavenger yields a H_(2)O_(2)-production rate of 1895 mol g^(-1)h^(-1).This study presents an example of a high-performance organic/inorganic S-scheme photocatalyst for H_(2)O_(2)production.展开更多
The photoconversion efficiency of semiconductor photocatalysts is severely hindered by uncontrolled recombination of photogenerated charge carriers 1-5.Investigating charge transfer dynamics and achieving manipulative...The photoconversion efficiency of semiconductor photocatalysts is severely hindered by uncontrolled recombination of photogenerated charge carriers 1-5.Investigating charge transfer dynamics and achieving manipulative carrier separation is of great interest.展开更多
Hydrogen(H_(2))is a clean,efficient,and renewable energy with zero carbon emission,which is expected to replace the extensively used fossil fuels.Photocatalytic water splitting is a promising strategy for sustainable ...Hydrogen(H_(2))is a clean,efficient,and renewable energy with zero carbon emission,which is expected to replace the extensively used fossil fuels.Photocatalytic water splitting is a promising strategy for sustainable H2 production.Nevertheless,the performance of single‐component photocatalysts is often confined by fast electron‐hole recombination due to strong Coulombic force,and their inability to simultaneously attain a wide absorption range and enough redox capabilities.These problems can be addressed by constructing a heterojunction between two semiconductors with different Fermi levels(EF),conduction band(CB)and valence band(VB)positions.Heterojunction promotes light harvesting through light absorption on both semiconductors and facilitates charge separation by decoupling them on different bands.There are mainly three types of heterojunctions,namely the type‐II heterojunction,the Z‐scheme heterojunction,and the step‐scheme(S‐scheme)heterojunction[1–3].In a type‐II heterojunction,photogenerated electrons migrate from the higher CB to the lower one,while photogenerated holes transfer from the lower to the higher VB.However,this schematic is thermodynamically flawed since the charge transfer discounts the redox powers of the electrons and holes.This transfer is also dynamically unfavorable due to strong repulsion between the photogenerated electrons(or holes)in different semiconductors.The Z‐scheme heterojunction utilizes dissolved redox ion pairs(traditional Z‐scheme)or conductive materials(all‐solid‐state Z‐scheme)as the shuttle for charge transfer and separation.However,the photogenerated carriers with stronger redox powers would preferentially react with the ion pairs or combine at the conductor because of stronger driving forces,leading to deducted redox powers and reduced photocatalytic activity.S‐scheme heterojunction could avoid these drawbacks and has exhibited excellent performance in organics degradation[4,5],CO_(2) reduction[6,7],hydrogen evolution[8],etc.展开更多
Noble metal cocatalysts have shown great potential in boosting the performance of CdS in photocatalytic water splitting.However,the mechanism and kinetics of electron transfer in noble-metal-decorated CdS during pract...Noble metal cocatalysts have shown great potential in boosting the performance of CdS in photocatalytic water splitting.However,the mechanism and kinetics of electron transfer in noble-metal-decorated CdS during practical hydrogen evolution is not clearly elucidated.Herein,Pt-nanoparticle-decorated CdS nanorods(CdS/Pt)are utilized as the model system to analyze the electron transfer kinetics in CdS/Pt heterojunction.Through femtosecond transient absorption spectroscopy,three dominating exciton quenching pathways are observed and assigned to the trapping of photogenerated electrons at shallow states,recombination of free electrons and trapped holes,and radiative recombination of locally photogenerated electron-hole pairs.The introduction of Pt cocatalyst can release the electrons trapped at the shallow states and construct an ultrafast electron transfer tunnel at the CdS/Pt interface.When CdS/Pt is dispersed in acetonitrile,the lifetime and rate for interfacial electron transfer are respectively calculated to be~5.5 ps and~3.5×10^(10) s^(−1).The CdS/Pt is again dispersed in water to simulate photocatalytic water splitting.The lifetime of the interfacial electron transfer decreases to~5.1 ps and the electron transfer rate increases to~4.9×10^(10) s^(−1),confirming that Pt nanoparticles serve as the main active sites of hydrogen evolution.This work reveals the role of Pt cocatalysts in enhancing the photocatalytic performance of CdS from the perspective of electron transfer kinetics.展开更多
Noble metal palladium(Pd)is well‐known as excellent photocatalytic cocatalyst,but its strong adsorption to hydrogen causes its limited H2‐evolution activity.In this study,the transition metal Cu was successfully int...Noble metal palladium(Pd)is well‐known as excellent photocatalytic cocatalyst,but its strong adsorption to hydrogen causes its limited H2‐evolution activity.In this study,the transition metal Cu was successfully introduced into the metallic Pd to weaken its hydrogen‐adsorption strength to improve its interfacial H_(2)‐evolution rate via the Pd‐Cu alloying effect.Herein,the ultrasmall Pd_(100−x)Cu_(x) alloy nanodots(2−5 nm)as a novel H_(2)‐evolution cocatalyst were integrated with the TiO_(2) through a simple NaH_(2)PO_(2)‐mediated co‐deposition route.The resulting Pd_(100−x)Cu_(x)/TiO_(2) sample shows the significantly enhanced photocatalytic H_(2)‐generation performance(269.2μmol h^(−1)),which is much higher than the bare TiO2.Based on in situ irradiated X‐ray photoelectron spectroscopy(ISI‐XPS)and density functional theory(DFT)results,the as‐formed Pd_(100−x)Cu_(x) alloy nanodots can effectively promote the separation of photo‐generated charges and weak the adsorption strength for hydrogen to optimize the process of hydrogen‐desorption process on Pd_(75)Cu_(25) alloy,thus leading to high photocatalytic H_(2)‐evolution activity.Herein,the weakened H adsorption of Pd_(75)Cu_(25) cocatalyst can be ascribed to the formation of electron‐rich Pd after the introduction of weak electronegativity Cu.The present work about optimizing electronic structure for promoting interfacial reaction activity provides a new sight for the development of the highly efficient photocatalysts.展开更多
文摘Hydrogen peroxide(H_(2)O_(2))has gained widespread attention as a versatile oxidant and a mild disin-fectant.Here,an electrostatic self-assembly method is applied to couple ZnSe quantum dots(QDs)with a flower-like covalent organic framework(COF)to form a step-scheme(S-scheme)photocata-lyst for H_(2)O_(2)production.The as-prepared S-scheme photocatalyst exhibits a broad light absorption range with an edge at 810 nm owing to the synergistic effect between the ZnSe QDs and COF.The S-scheme charge-carrier transfer mechanism is validated by performing Fermi level calculations and in-situ X-ray photoelectron and femtosecond transient absorption spectroscopies.Photolumi-nescence,time-resolved photoluminescence,photocurrent response,electrochemical impedance spectroscopy,and electron paramagnetic resonance results show that the S-scheme heterojunction not only promotes charge carrier separation but also boosts the redox ability,resulting in enhanced photocatalytic performance.Remarkably,a 10%-ZnSe QD/COF has excellent photocatalytic H_(2)O_(2)-production activity,and the optimal S-scheme composite with ethanol as the hole scavenger yields a H_(2)O_(2)-production rate of 1895 mol g^(-1)h^(-1).This study presents an example of a high-performance organic/inorganic S-scheme photocatalyst for H_(2)O_(2)production.
文摘The photoconversion efficiency of semiconductor photocatalysts is severely hindered by uncontrolled recombination of photogenerated charge carriers 1-5.Investigating charge transfer dynamics and achieving manipulative carrier separation is of great interest.
基金supported by the Institutional Fund Projects under grant no(IFPRC‐133‐130‐2020).Therefore,authors gratefully acknowledge technical and financial support from Ministry of Education and King Abdulaziz University,Jeddah,Saudi Arabia.
文摘Hydrogen(H_(2))is a clean,efficient,and renewable energy with zero carbon emission,which is expected to replace the extensively used fossil fuels.Photocatalytic water splitting is a promising strategy for sustainable H2 production.Nevertheless,the performance of single‐component photocatalysts is often confined by fast electron‐hole recombination due to strong Coulombic force,and their inability to simultaneously attain a wide absorption range and enough redox capabilities.These problems can be addressed by constructing a heterojunction between two semiconductors with different Fermi levels(EF),conduction band(CB)and valence band(VB)positions.Heterojunction promotes light harvesting through light absorption on both semiconductors and facilitates charge separation by decoupling them on different bands.There are mainly three types of heterojunctions,namely the type‐II heterojunction,the Z‐scheme heterojunction,and the step‐scheme(S‐scheme)heterojunction[1–3].In a type‐II heterojunction,photogenerated electrons migrate from the higher CB to the lower one,while photogenerated holes transfer from the lower to the higher VB.However,this schematic is thermodynamically flawed since the charge transfer discounts the redox powers of the electrons and holes.This transfer is also dynamically unfavorable due to strong repulsion between the photogenerated electrons(or holes)in different semiconductors.The Z‐scheme heterojunction utilizes dissolved redox ion pairs(traditional Z‐scheme)or conductive materials(all‐solid‐state Z‐scheme)as the shuttle for charge transfer and separation.However,the photogenerated carriers with stronger redox powers would preferentially react with the ion pairs or combine at the conductor because of stronger driving forces,leading to deducted redox powers and reduced photocatalytic activity.S‐scheme heterojunction could avoid these drawbacks and has exhibited excellent performance in organics degradation[4,5],CO_(2) reduction[6,7],hydrogen evolution[8],etc.
文摘Noble metal cocatalysts have shown great potential in boosting the performance of CdS in photocatalytic water splitting.However,the mechanism and kinetics of electron transfer in noble-metal-decorated CdS during practical hydrogen evolution is not clearly elucidated.Herein,Pt-nanoparticle-decorated CdS nanorods(CdS/Pt)are utilized as the model system to analyze the electron transfer kinetics in CdS/Pt heterojunction.Through femtosecond transient absorption spectroscopy,three dominating exciton quenching pathways are observed and assigned to the trapping of photogenerated electrons at shallow states,recombination of free electrons and trapped holes,and radiative recombination of locally photogenerated electron-hole pairs.The introduction of Pt cocatalyst can release the electrons trapped at the shallow states and construct an ultrafast electron transfer tunnel at the CdS/Pt interface.When CdS/Pt is dispersed in acetonitrile,the lifetime and rate for interfacial electron transfer are respectively calculated to be~5.5 ps and~3.5×10^(10) s^(−1).The CdS/Pt is again dispersed in water to simulate photocatalytic water splitting.The lifetime of the interfacial electron transfer decreases to~5.1 ps and the electron transfer rate increases to~4.9×10^(10) s^(−1),confirming that Pt nanoparticles serve as the main active sites of hydrogen evolution.This work reveals the role of Pt cocatalysts in enhancing the photocatalytic performance of CdS from the perspective of electron transfer kinetics.
文摘Noble metal palladium(Pd)is well‐known as excellent photocatalytic cocatalyst,but its strong adsorption to hydrogen causes its limited H2‐evolution activity.In this study,the transition metal Cu was successfully introduced into the metallic Pd to weaken its hydrogen‐adsorption strength to improve its interfacial H_(2)‐evolution rate via the Pd‐Cu alloying effect.Herein,the ultrasmall Pd_(100−x)Cu_(x) alloy nanodots(2−5 nm)as a novel H_(2)‐evolution cocatalyst were integrated with the TiO_(2) through a simple NaH_(2)PO_(2)‐mediated co‐deposition route.The resulting Pd_(100−x)Cu_(x)/TiO_(2) sample shows the significantly enhanced photocatalytic H_(2)‐generation performance(269.2μmol h^(−1)),which is much higher than the bare TiO2.Based on in situ irradiated X‐ray photoelectron spectroscopy(ISI‐XPS)and density functional theory(DFT)results,the as‐formed Pd_(100−x)Cu_(x) alloy nanodots can effectively promote the separation of photo‐generated charges and weak the adsorption strength for hydrogen to optimize the process of hydrogen‐desorption process on Pd_(75)Cu_(25) alloy,thus leading to high photocatalytic H_(2)‐evolution activity.Herein,the weakened H adsorption of Pd_(75)Cu_(25) cocatalyst can be ascribed to the formation of electron‐rich Pd after the introduction of weak electronegativity Cu.The present work about optimizing electronic structure for promoting interfacial reaction activity provides a new sight for the development of the highly efficient photocatalysts.
