Preparation And Photocatalytic Performance Of Nano Zinc Oxide And Its Composites

As one of the most promising semiconductor photocatalysts, Zn O has gotten an extensive emphasis due to its application in the degradation of environmental pollutants. With the continuous development of semiconductor photocatalysts, a higher requirement is devoted to their properties. Thus, it is necessary to develop a thoroughly purified, enviromental friendly, economic and efficient photocatalyst with mild reaction condition. Graphene, a monolayer sp2 carbon atoms has superior electrical conductivity and mechanical properties which makes it an outstanding electron-transport material in the process of photocatalysis. Considering the individual effects of Ag nanoparticles and graphene on the enhancement of photocatalytic activity of Zn O, it was a meaningful research to combine these different materials into a heterostrcuture for the performance improvement of semiconductor photocatalysts.Graphite oxide(GO) was prepared using the Hummers method with slight modifications. Zn O, Ag/Zn O and Ag/Zn O/graphene samples were synthesized by a facile low-temperature microwave-assisted solution method. The TEM image of Ag/Zn O/graphene presents the intimate contact between Zn O and graphene. In addition, Ag nanoparticles are attached to Zn O nanorods and dispersed on the surface of the graphene sheets. This intimate contact makes the possible electronic interaction among Zn O, Ag, and graphene and enhances the charge separation and the photocatalytic activity.In this paper, the photocatalytic performance of Zn O, Ag/Zn O and Ag/Zn O/graphene were evaluated by the degradation of MO(20 mg/L) solution. During the experimental process, the concentration of photocatalyst is 1 g/L. At an interval of 10 min, about 3 m L of the suspension was sampled from the system and centrifuged to separate the residual catalysts and then the absorbance intensity was measured at the wavelength of 464 nm. For MO solution in the presence of Zn O, Ag/Zn O and Ag/Zn O/graphene, the degradation rate are 58.8%, 71.6% and 97.4% separately after 80 min of UV irradiation. The results show that the photocatalytic activity of Zn O can be improved by incorporation of Ag. The addition of graphene can enhance the photocatalytic performance significantly. It is commonly believed that the lower of excitonic PL intensity, the higher the separation rate of photo-induced charge carriers. The PL intensities of these samples increase in the following order: Ag/Zn O/graphene, Ag/Zn O and Zn O. Thus, the photocatalytic performance of Zn O can be improved greatly with the addition of Ag and graphene. In addition, Ag/Zn O/graphene photocatalysts with different amounts of graphene loading show different photocatalytic activity. Ag/Zn O/graphene nanocomposites exhibit the highest photocatalytic activity when the content of graphene is 1.0 wt%. When the loading amount was below 1.0 wt%, the photocatalytic activities improved with the increase of graphene amount. However, when the loading amount exceeded 1.0 wt%, the photocatalytic activities of Ag/Zn O/graphene samples decreased as the amount of graphene increased. For a practical photocatalyst, the photocatalytic stability and the reuse of the catalyst are crucial. Recycled experiments for the photodegradation of MO under UV irradiation were conducted to study the photostability of the Ag/Zn O/graphene nanocomposites which the GO content is 1%. The degradation rate after the first cycle is 96.8% and the degradation percentage is 92.7% after five cycles. This result shows that the photocatalytic activity of Ag/Zn O/graphene has no significant change after five cycles. In other words, Ag/Zn O/graphene exhibits excellent photostability.