The influence of surface S^2- dangling bonds and surface doped ions（Se^2-, Cu^2＋, and Hg^2＋） on the photoluminescence of Cd^2＋-rich CdS QDs was investigated. A quantitative model was proposed to understand the co...The influence of surface S^2- dangling bonds and surface doped ions（Se^2-, Cu^2＋, and Hg^2＋） on the photoluminescence of Cd^2＋-rich CdS QDs was investigated. A quantitative model was proposed to understand the complex transfer processes of excited electrons in CdS QDs. The transfer of excited electrons from either the conduction band or the Cd^2＋-related trap-state to the surface S^2-related shallow hole trap-state is effective. However, the trap of excited electrons by surface doped ion trap-states from the Cd^2＋-related trap-state is more effective than that from the conduction band. The efficiency of trapping electrons from both the conduction band and the Cd^2＋-related trap-state can be quantitatively understood with the help of the proposed model. The results show that the transfer efficiency of excited electrons is dependent on the location of the energy-level of the relevant surface-related trap-state. The trap of excited electrons by the surface trap-state with energy-level closer to that of the conduction band is more effective, especially for the trap of excited electrons from Cd^2＋-related trap-state.展开更多
The production of renewable fossil fuels such as CH_(4) and CO by photocatalytic CO_(2)reduction has attracted more and more attention.However,single photocatalyst is less efficient for photocatalytic reduction of CO_...The production of renewable fossil fuels such as CH_(4) and CO by photocatalytic CO_(2)reduction has attracted more and more attention.However,single photocatalyst is less efficient for photocatalytic reduction of CO_(2)due to the fast recombination of photogenerated electron pairs.Herein,we successfully prepare CdS-Ag_(2)S composite by assembling the Ag_(2)S QDs cocatalyst on the surface of CdS nanosheet-assembled flower through oil-bath solvothermal method.This composite is prepared through a simple self-assembly strategy using cadmium chloride,ammonia and thiourea as precursors of the CdS nanosheet-assembled flower and silver nitrate and 3-mercaptopropionic acid as the precursors of Ag_(2)S QDs.The average diameter of Ag_(2)S QDs is apparently 6.0 nm.The light absorption edge of the composite is at around 560 nm,with the corresponding band gap at 2.14 eV.The CdS-Ag_(2)S QDs composite with 5 wt%Ag_(2)S QDs loaded achieves CO evolution rate of 16.6μmol·g^(-1)·h^(-1)without noble-metal cocatalysts.This strengthened photocatalytic performance and photocatalytic stability were attributed to the energy band broadening of Ag_(2)S QDs caused by quantum size effect and the large specific surface area due to the assembled flower.The mechanism underlying the enhanced photocatalytic CO_(2)reduction activity is further proposed.This study demonstrates that semiconductor-based quantum dots are strong candidates for excellent cocatalysts in photocatalysis.展开更多
The advancement of electrocatalytic N2 reduction reaction (NRR) toward ambient NH3 synthesis lies in the development of more affordable electrocatalysts than noble metals. Recently, various nanostructures of transitio...The advancement of electrocatalytic N2 reduction reaction (NRR) toward ambient NH3 synthesis lies in the development of more affordable electrocatalysts than noble metals. Recently, various nanostructures of transition metal compounds have been proposed as effective electrocatalysts;however, they exist in the form of loose powders, which have to be immobilized on a matrix before serving as the electrode for electrolysis. The matrix, being it carbon paper, carbon cloth or metal foam, is electrocatalytically inactive, whose introduction inevitably raises the invalid weight while sacrificing the active sites of the electrode. Herein, we report on the fabrication of a flexible ZrO2 nanofibrous membrane as a novel, self-supported electrocatalyst. The heteroatom doping can not only endow the nanofibrous membrane with excellent flexibility, but also induce oxygen vacancies which are responsible for easier adsorption of N2 on the ZrO2 surface. To improve the electrocatalytic activity, a facile SILAR approach is employed to decorate it with CdS quantum dots (QDs), thereby tuning its Fermi level. To improve the conductivity, a g-C3N4 nanolayer is further deposited which is both conductive and active. The resulting hierarchically structured, self-supported electrocatalyst, consisting of g-C3N4 encapsulated ZrO2 nanofibrous membrane decorated with CdS QDs, integrates the merits of the three components, and exhibits a remarkable synergy toward NRR. Excellent NH3 yield of 6.32 × 10−10 mol·s−1cm−2 (−0.6 V vs. RHE) and Faradaic efficiency of 12.9% (−0.4 V vs. RHE) are attained in 0.1 M Na2SO4.展开更多
The diffusion-controlled growth mode is widely used to narrow the size distribution of colloidal quantum dots.However,this growth mode always suffers from size broadening at the later growth stage.By monitoring the gr...The diffusion-controlled growth mode is widely used to narrow the size distribution of colloidal quantum dots.However,this growth mode always suffers from size broadening at the later growth stage.By monitoring the growth process of CdS colloidal quantum dots,we show the size broadening is a result of different growth rates of CdS colloidal quantum dots(CQDs)with different morphologies.Monomer concentration-dependent growth experiments demonstrate the different growth rates are caused by the different ligand permeabilities of CdS CQDs.The cubic ones have lower ligand permeability but higher saturated surface reaction rate than the noncubic ones,leading to unexpected narrower size distribution under higher monomer concentration.More efficient narrowing can be obtained by the addition of chloride ions,which can increase the ligand permeability of all CdS CQDs,as well as the opposite discrepancies in ligand permeability and surface reaction between cubic and noncubic CdS CQDs.The photoluminescence(PL)full width at half maximum(FWHM)of CdS CQDs can be narrowed down to below 80 meV for PL peaks from 430 to 500 nm.Given the inevitable usage of the ligands in the solution synthesis of colloidal nanocrystals,the influence of morphology difference on growth rate should be common.Our results can provide an alternative solution to realize size focusing for the synthesis of colloidal nanocrystals.展开更多
基金Supported by the Measurement and Testing Center of Zhejiang Province, China(No.02079).
文摘The influence of surface S^2- dangling bonds and surface doped ions（Se^2-, Cu^2＋, and Hg^2＋） on the photoluminescence of Cd^2＋-rich CdS QDs was investigated. A quantitative model was proposed to understand the complex transfer processes of excited electrons in CdS QDs. The transfer of excited electrons from either the conduction band or the Cd^2＋-related trap-state to the surface S^2-related shallow hole trap-state is effective. However, the trap of excited electrons by surface doped ion trap-states from the Cd^2＋-related trap-state is more effective than that from the conduction band. The efficiency of trapping electrons from both the conduction band and the Cd^2＋-related trap-state can be quantitatively understood with the help of the proposed model. The results show that the transfer efficiency of excited electrons is dependent on the location of the energy-level of the relevant surface-related trap-state. The trap of excited electrons by the surface trap-state with energy-level closer to that of the conduction band is more effective, especially for the trap of excited electrons from Cd^2＋-related trap-state.
基金partially supported by the National Natural Science Foundation of China(No.51672099 and 52073263)the Open Foundation of State Key Laboratory of Electronic Thin Films and Integrated Devices(No.KFJJ202105)Fundamental Research Funds for the Central Universities(No.2017-QR-25)。
文摘The production of renewable fossil fuels such as CH_(4) and CO by photocatalytic CO_(2)reduction has attracted more and more attention.However,single photocatalyst is less efficient for photocatalytic reduction of CO_(2)due to the fast recombination of photogenerated electron pairs.Herein,we successfully prepare CdS-Ag_(2)S composite by assembling the Ag_(2)S QDs cocatalyst on the surface of CdS nanosheet-assembled flower through oil-bath solvothermal method.This composite is prepared through a simple self-assembly strategy using cadmium chloride,ammonia and thiourea as precursors of the CdS nanosheet-assembled flower and silver nitrate and 3-mercaptopropionic acid as the precursors of Ag_(2)S QDs.The average diameter of Ag_(2)S QDs is apparently 6.0 nm.The light absorption edge of the composite is at around 560 nm,with the corresponding band gap at 2.14 eV.The CdS-Ag_(2)S QDs composite with 5 wt%Ag_(2)S QDs loaded achieves CO evolution rate of 16.6μmol·g^(-1)·h^(-1)without noble-metal cocatalysts.This strengthened photocatalytic performance and photocatalytic stability were attributed to the energy band broadening of Ag_(2)S QDs caused by quantum size effect and the large specific surface area due to the assembled flower.The mechanism underlying the enhanced photocatalytic CO_(2)reduction activity is further proposed.This study demonstrates that semiconductor-based quantum dots are strong candidates for excellent cocatalysts in photocatalysis.
基金This work was financially supported by the Fundamental Research Funds for the Central Universities(No.2232019G-01)the National Natural Science Foundation of China(Nos.21961132024,51925302 and 51873029)+3 种基金the Natural Science Foundation of Shanghai(No.19ZR1401100)the Innovation Program of Shanghai Municipal Education Commission(No.2017-01-07-00-03-E00024)the Program of Shanghai Academic Research Leader(No.18XD1400200)the DHU Distinguished Young Professor Program(No.LZA2020001).
文摘The advancement of electrocatalytic N2 reduction reaction (NRR) toward ambient NH3 synthesis lies in the development of more affordable electrocatalysts than noble metals. Recently, various nanostructures of transition metal compounds have been proposed as effective electrocatalysts;however, they exist in the form of loose powders, which have to be immobilized on a matrix before serving as the electrode for electrolysis. The matrix, being it carbon paper, carbon cloth or metal foam, is electrocatalytically inactive, whose introduction inevitably raises the invalid weight while sacrificing the active sites of the electrode. Herein, we report on the fabrication of a flexible ZrO2 nanofibrous membrane as a novel, self-supported electrocatalyst. The heteroatom doping can not only endow the nanofibrous membrane with excellent flexibility, but also induce oxygen vacancies which are responsible for easier adsorption of N2 on the ZrO2 surface. To improve the electrocatalytic activity, a facile SILAR approach is employed to decorate it with CdS quantum dots (QDs), thereby tuning its Fermi level. To improve the conductivity, a g-C3N4 nanolayer is further deposited which is both conductive and active. The resulting hierarchically structured, self-supported electrocatalyst, consisting of g-C3N4 encapsulated ZrO2 nanofibrous membrane decorated with CdS QDs, integrates the merits of the three components, and exhibits a remarkable synergy toward NRR. Excellent NH3 yield of 6.32 × 10−10 mol·s−1cm−2 (−0.6 V vs. RHE) and Faradaic efficiency of 12.9% (−0.4 V vs. RHE) are attained in 0.1 M Na2SO4.
基金the Start-up Funding of ShanghaiTech University,the National Natural Science Foundation of China(No.21902142)the Key Laboratory of Excited-State Materials of Zhejiang Province,Zhejiang University。
文摘The diffusion-controlled growth mode is widely used to narrow the size distribution of colloidal quantum dots.However,this growth mode always suffers from size broadening at the later growth stage.By monitoring the growth process of CdS colloidal quantum dots,we show the size broadening is a result of different growth rates of CdS colloidal quantum dots(CQDs)with different morphologies.Monomer concentration-dependent growth experiments demonstrate the different growth rates are caused by the different ligand permeabilities of CdS CQDs.The cubic ones have lower ligand permeability but higher saturated surface reaction rate than the noncubic ones,leading to unexpected narrower size distribution under higher monomer concentration.More efficient narrowing can be obtained by the addition of chloride ions,which can increase the ligand permeability of all CdS CQDs,as well as the opposite discrepancies in ligand permeability and surface reaction between cubic and noncubic CdS CQDs.The photoluminescence(PL)full width at half maximum(FWHM)of CdS CQDs can be narrowed down to below 80 meV for PL peaks from 430 to 500 nm.Given the inevitable usage of the ligands in the solution synthesis of colloidal nanocrystals,the influence of morphology difference on growth rate should be common.Our results can provide an alternative solution to realize size focusing for the synthesis of colloidal nanocrystals.
