Preparation And Investigation On Photocatalytic Performances Of G-C₃N₄ Based Hollow Composite Photocatalysts

Photocatalytic materials have been placed high hopes in solving environmental and energy problems due to their potential applications in the field of photodegradation,CO2 reduction,water splitting,etc.However,the wide band gap and high recombination efficiency of electron-hole pairs of the traditional photocatalysts have greatly restricted their practical applications.In order to improve the performance of photocatalytic materials,new strategyies and designs have to be developed.In this thesis,two kinds of Z-Scheme composite photocatalytic materials with hollow structure were prepared based on g-C3N4.These photocatalysts exhibited improved activities in the photocatalytic degradation of antibiotics,dyes and CO2 reduction.The main investigations and conclusions are summarized as follows,1.WO3/g-C3N4 hollow microspheres composite were successfully prepared by in-situ hydrolysis and high temperature polymerization.The structure and composition of WO3/g-C3N4 were analyzed by XRD,FT-IR and XPS,these confirmed that the composites is constituted by WO3 and g-C3N4.SEM and TEM demonstrated that the different ratios of precursors for WO3 and g-C3N4 had great influence on the morphology of the composites.Integratd and well-defined hollow microspheres would be been built when the ratios of precursors for WO3 and g-C3N4 was 1:4.2.WO3/g-C3N4 composites showed enhanced photocatalytic degradation performance under visible light irradiation.The best degradation efficiency for tetracyclin HC1 and CFS reached 82%and 70%in 2h,respectively.The capture experiment for active species and ESR test validated that WO3/g-C3N4 composites had a Z-Scheme photocatalytic degradation mechanism.Formation of heterojunctions greatly promoted the separation of photogeneratd electron-hole pairs,and thus the antibiotic degradation abilities were improved.3.Series of LDH/RGO/g-C3N4 composites were prepared by a facile hydrothermal method.The structure and composition of these composites were characterized by XRD,FT-IR,Raman and XPS.LDH/RGO/g-C3N4 showed enhanced photocatalytic performances in the reduction of CO2 and degradation of methylene blue.Among all of the samples,LDH-RGO-CN-2 exhibited the best photocatalytic activity,the yield of methane reached 2.55 μmol/g and the degradation rate of MB reached 99%.4.The results of instantaneous photocurrent and AC impedance showed that LDH-RGO-CN-2 had the highest carrier mobility and photogenerated electron-hole separation efficiency.These confirmed that the addition of RGO promoted the charge transfer between LDH and g-C3N4,which effectively prevented the recombination of the photogenerated electron and hole.Therefore,photocatalytic activity of LDH-RGO-CN-2 was effectively enhanced.