Preparation And Photocatalytic Modification Of ZnO Quantum Dots

The optical and electrical behaviors of quantum dots(QDs)material are highly sensitive to size.A semiconductor photocatalyst based on ZnO QDs stands out from many catalysts by its advantages of non-toxic and tasteless and high surface activity.This work took ZnO QDs as the research substrate improved its preparation technique,explored the synthesis and photocatalytic properties of Cd-doped ZnO QDs and the nano-core-shell composites with Ag composite ZnO QDs.The prime tasks are as below:(1)Controlling different experimental preparation conditions to explore the best preparation process of Sol-Gel synthesis ZnO QDs.The synthesized samples were characterized using X-ray diffraction(XRD),transmission electron microscopy(HRTEM),X-ray photoelectron spectroscopy(XPS),field emission scanning electron microscope(FESEM)ultraviolet and visible light absorption spectrum(UV-vis),and photoluminescence spectroscopy(PL).And explored the optimal conditions for sample preparation which is helpful to improve photocatalytic performance.The best sample was found to degrade 91.3%methylene blue(MB)solution under 120 min irradiation.According to the results,the optimum preparation conditions:the molar ratio of Zn²⁺:OH^-was 1:5,preparation temperature 50?,and reaction time 20 min,respectively.(2)Doping is an effective functional modification method for improving the properties of semiconductors.Cd-doped wurtzite ZnO quantum dots(ZQ)zero-dimensional nanomaterials were successfully prepared by a simple and low-cost synthesis method.The samples were studied by XRD,HRTEM,XPS,UV-vis,PL,energy dispersive spectrometer(EDS).Meanwhile,simulate and calculate the bandgap change of ZnO after introducing Cd.The MB degradation efficiency of the sample with suitable dopant concentration(Cd content 0.5 wt%)was 96.5%under 80 min visible light irradiation.The obvious performance improvement is due to shortening the bandgap,the optical response is raised,the decrease of the carrier recombination rate,and the ZnO QDs own strong redox ability.(3)Remarkable progress has been made concerning heterogeneous visible light photocatalysis in the development of metal/semiconductor materials.In this study,pristine ZnO QDs(ZQ)and Ag/ZQ nanocomposites with different Ag loadings were prepared using a cost-effective method.The abundant surface oxygen vacancies(V_O)on ZQ improved the bandgap of Ag/ZQ nanocomposites.The prepared samples were examined by XRD,HRTEM,XPS,and electron paramagnetic resonance(EPR).Photocatalytic experiments indicated that the Ag11/ZQ(Ag loading 11 wt%)nanocomposite,exhibited prominent visible-light photocatalytic degradation activity for MB which presented a degradation efficiency of 99.4%after 80 min.UV-vis,PL,electrochemical impedance spectroscopy(EIS),time-resolution photoluminescence(TRPL)analyses,and density functional simulation computations confirmed the good visible-light activity of Ag/ZQ nanocomposites as photocatalysts.