Functional Modifications Of Zinc Oxide And Its Photocatalytic Performance For Dye Pollutions

In recent years, semiconductor photocatalytic oxidation is considered as a promising technology for the degradation of persistent organic pollutants, and can mineralize organic pollutants into more biologically degradable and less toxic substances. Zinc oxide (ZnO), as an important semiconductor, exhibits a promising prospect of application in the photocatalytic degradation of organic pollutants. However, because of the quick recombination of charge carriers, low quantum yield, poor response to solar light and critical drawback of photocorrosion. the utilization of ZnO is limited severely. Therefore, how to enhance the photocatalytic activity of ZnO, improve its response to visible light and inhibit its photocorrosion are receiving more and more scientific interests.In this paper, ZnO nanopowder was firstly synthesized from zinc acetate and diethylene glycol via an ultrasound assisted non-hydrolytic sol-gel process. The samples were characterized by X-ray diffraction (XRD). Transmission electron microscopy (TEM) and UV-Vis spectroscopy. The photocatalytic activity of prepared zinc oxide was evaluated by photocatalytic degradation of C.I. Acid Red249(AR249) under UV irradiation. The acoustic cavitations produced by ultrasonic waves could generate high pressure and temperature followed by high rate of cooling, which facilitated the ester-elimination reaction between zinc acetate and diethylene glycol. After dehydration and nucleation, the zinc oxide nanopowder formed. The prepared ZnO nanopowder showed good photocatalytic activity. After120min UV irradiation,20mg/L AR249was almost decomposed in the presence of0.8g/L ZnO nanopowder.The ZnO-SnO2photocatalyst was prepared by directly precipitation method. And the effects of calcination temperature, Sn/Zn molar ratio, the concentration of reactant and reaction temperature on their photocatalytic activity were discussed. The results showed when Sn/Zn molar ratio was1:4, the concentration of Zn2+was0.12mol/L, the calcination temperature and time was700℃and2h, the photocatalytic activity of ZnO-SnO2composite materials was best, which was higher than that of pure ZnO.ZnO/reduced graphene oxide (ZnO/rGO) composites were prepared through thermal decomposition of zinc acetate precursor in the presence of graphene oxide. The as-prepared samples were characterized by Fourier-transform infrared spectra (FTIR), X-ray diffraction (XRD), Transmission electron microscopy (TEM), Raman, UV-Vis diffuse reflectance spectroscopy (DRS). The formation mechanism of ZnO/rGO composites was proposed. Under high temperature, the graphene oxide was reduced by diethylene glycol (DEG). Simultaneously, Zn2+hydrolyzed, nucleated and consequently formed ZnO on the surface of layered graphene sheets. The promotion of charge transportation and separation resulting from the interaction between ZnO and rGO improved the photocatalytic activity of ZnO/rGO composites and inhibited the photocorrosion of ZnO.Poly(m-phenylenediamine)/ZnO (PMPD/ZnO) composites were successfully synthesized by chemical oxidative polymerization method. Powder X-ray diffraction (XRD), Fourier-transform infrared spectra (FTIR), Transmission electron microscope (TEM) and UV-vis (UV-vis) spectra were used to characterize the prepared PMPD/ZnO composites. Their photocatalytic activities were evaluated by the degradation of C.I. Acid Red249(AR249) aqueous solution under UV and visible light irradiations. Results showed that PMPD/ZnO composites exhibited good photocatalytic activities under UV and visible light irradiations, whereas neat ZnO had only ultraviolet light photocatalytic activity. Moreover, PMPD/ZnO composites had better photocatalytic stabilities. After five successive cycles, their photocatalytic activities for degradation of AR249were still over75%of that for the first cycling run under UV and visible light irradiations.