Preparation And Photocatalytic Properties Of Zinc Oxide/Graphene Composites

Nowadays, the growing population has led to the increase mainly contamination ofsurface water and underground water. Organic dyes used in textile and food industriesare their important sources of the environmental contaminations due to their non-biodegradability and high toxicity to aquatic creatures and carcinogenic effects onhumans. In order to decrease damage caused by organic dye pollution to environmentand humans, the use of photocatalyst to degrade organic compounds in contaminatedair or water or to convert them into harmless chemicals has been extensively studied.A major limitation to achieve high photocatalytic efficiency is the quickrecombination of photo-generated charge carries. Recombination has faster kineticsthan surface redox reactions and greatly reduces the quantum efficiency ofphotocatalysis. Therefore, to enhance the photocatalysis efficiency, it is essential toretard the recombination of the charge carriers.Zinc oxide （ZnO） photocatalyst has been paid much attention because of its highchemical stabilizations for its non-toxicity and abundance in nature. In order toimprove the photocatalytic activity, different kinds of ions have been doped into ZnOto inhibit the recombination of photoinduced electrons and holes. Another option tosolve faster recombination kinetics problem is to design and develop compositematerials such as ZnO/CeO₂nanofibers, ZnO/montmorillonite, Cu₂O nanoparticlessensitized ZnO nanorod arrays, SnO₂/ZnO/TiO₂, ZnO–reduced graphene oxide （GO）composites. As a non-energy-gap semiconductor, graphene exhibits fascinatingtransport phenomenon and ultrahigh carrier mobility. Taking into account theexcellent individual properties of GO and ZnO, the composition of GO with ZnOnanoparticles has given enhanced photocatalytic performances. This dissertationconsists of following contents. （1）we have prepared the graphite oxide by Hummers method using nature graphiteflakes. The exfoliated graphene oxide was prepared after the ultrasonic processingthen reduced via chemistry method to the graphene sheets. X-ray diffraction （XRD）and transmission electron microscope （TEM）) were used to characterize the crystalstructure.（2）The zinc oxide-graphene oxide （ZnO-GO） composites have been prepared inhydrothermal synthesis by using GO dispersed in the ethanol as carrier, zinc acetatedihydrate and ammonium hydroxide as reactant. The reduction of the GO in thecomposites was coducted with UV-irradiation assistantly treating ZnO-GO. Thephotodegradation of methylene blue has been investigated in the presence of theprepared composites. The effects GO content, hydrothermal synthesis temperature,time and UV-irradiation time on the degradation rate of methyl blue have beeninvestigated, respectively. The samples were characterized by using XRD, SEM,X-ray photoelectron spectroscopy.（3） In this work, ZnO/Cu₂O composites were grown on graphene oxide （GO） films byusing simple hydrothermal method. The optical and structural properties of theZnO/Cu₂O/GO nanoparticles were systematically studied by SEM, TEM,（XRD），XPS and ultraviolet-visible spectroscopy. The XRD patterns, SEM and TEM imagesshow that ZnO displays a hexagonal nanorod structure. It is clearly observed thatZnO/Cu₂O nanorods were supported on the surface of GO sheets. Their photocatalyticdegradation of Indigo Carmine was investigated. The results show that the cuprousoxide （Cu₂O） plays an important role in the enhancement of the photocatalyticdegradation. When the atom ratio of Zn/Cu is5/2,120℃of hydrothermalsynthesis temperature and20h of synthesis time, the ZnO/Cu₂O/GO compositeexhibits good photocatalytic activity with96.5%degradation rate of indigo carmineaqueous solution under500W high pressure Hg lamp irradiation for240min ascompared with ZnO/Cu₂O （77.5%）,ZnO/GO （91.28%）. Three effective factors ofphotacatalytic activity namely, the content of Cu₂O doping in the ZnO samples,hydrothermal synthesis temperature and time have been optimized based on thephotocatalytic degradation of Indigo carmine solution.