Investigation Of Preparation And Photocatalytic Performances Of Sheets/Dumbbell/Urchin-like Ultra-structure ZnO And Its' Composites

Zinc oxide(ZnO)as a typical group II-IV semiconductor oxide material has proven widely investigated due to its excellent optical and electronic performances,especially in field of energy storage and environmental purification.However,some major stumbling blocks such as low efficiency of energy conversion,high recombination of photogenerated electron-hole pairs,photo-induced corrosion,etc hinder ZnO practical applications.As we all know,the photoelectrochemical(PEC)performances of photocatalysts are closely related to morphology and structure.Hence,preparing a high-performance ZnO,which has some merits such as high separation of electron-hole pairs,reusability and high utilization of solar energy,has been become an emergency.Herein,nanosheet/dumbbell-shape,urchin-like ultra-structure ZnO with different morphology and corresponding derivative graphite-like materials/ZnO composites were fabricated by a facile hydrothermal process,and the effects of reactive conditions on morphology and structure of ZnO were investigated.Furthermore,base on the reactive specie trapping experiments,the proposed photodegradation mechanism for removal pollution was research..The major work has focused on the following:(1)Inspired by nanosheets to promote the separation of electron-hole pairs,a novel self-growing ZnO with numerous nanosheets grown on the surface of dumbbell-shape have been successfully synthesized via a simple hydrothermal route,meanwhile,the nanosheet was exposed high-energy(101)crystal plane.The effects between hydrothermal time and crystal growing of dumbbell-shape ZnO were investigated by XRD,SEM,TEM,DRS and EIS,and the optimized prepared condition was obtained.The photocatalytic experimental results shown that the exposed(101)nanosheets/dumbbell-shape ZnO not only dominantly promote charge generation,separation and transfer(the conductive value nearly decreased 1/2),but also exhibited an excellent photodegradation ratio of RhB wastewater(rate constant k=46.00×10-3 min-1)that was more than 3-folds that than of the complete structure of dumbbell-shape ZnO.According to characteristic and experimental results,a photocatalytic mechanism was proposed,which demonstrate the excellent photocatalytic activity of ZnO.(2)Based on the previous nanosheet/dumbbell ZnO research,a series of RGO/ZnO composites with different concentration gradients were fabricated by second hydrothermal route,and all resultants were characterization and measured.Furthermore,the effects of different weights of graphene introduction system on the PEC performances of ZnO were investigated.The FT-IR results display that reduction degree of graphene oxide was related to hydrothermal time and temperature.The photocatalytic results exhibited that the photocatalytic performances of RGO/ZnO composites enhanced with graphene content increase.When the weight ratio of graphene is 1.5wt%,the composite shows optimized photocatalytic activity(kRhB=56.23×10-3 min-1);however,when the weight ratio over 1.5wt%,the photocatalytic activity of composite was decreased due to excessive graphene generating new active sites or competitive absorption.Owing to the introduction of graphene to inhibit the photo-induced corrosion in photocatalytic process of ZnO,as-prepared 1.5wt%RGO/ZnO composite show a stable and reusable catalytic performance.After four cycling runs photocatalytic process toward RhB,the activity of above-mentioned composite shows an excellent rate constant that is about 53.50×10-3 min-1.(3)Herein,a series of MoS2/ZnO composites were successfully fabricated via facile hydrothermal route using Na2MoO4,(NH2)2CS and urchin-like ZnO as precursors.According to the results of XRD and XPS,it was found that ZnS appeared in MoS2/ZnO composite,meanwhile,the content was positively correlated with the weight of the precursor(NH2)2CS.It should be noted that the morphology and the metallic phase content of MoS2 in-situ grown on the surface of ZnO were affected by the molar ratio of Na2MoO4 and ZnO.Benefiting from the special dual II heterojunctions of MoS2/ZnS/ZnO ternary composite,the material exhibited excellent charge separation,transfer performances and then increased the photocatalytic activities.In the photocatalytic measurements,the MoS2/ZnS/ZnO composite(Na2MoO4:ZnO 1:2 MZ2)not only exhibits excellent photocatalytic Cr(VI)reduction activity(k=42.3×10-3 min-1),but also displays remarkable adsorption performance(32.1%).In addition,MZ2 ternary composite shows dominant photocatalytic Cr(VI)reduction activities than that of other photocatalysts.