Graphene and Graphene-Metal Nanocomposites Prepared through the Photocatalytic Reduction of Graphene Oxide Using the Polyoxometalate

MasterGraphene is a single layer of sp2 hybrid carbon atoms closely packed in a two-dimensional honeycomb lattice, which has been intensively researched since the existence of free-standing 2D atomic crystals was discovered by Geim group. Graphene has been interested in many research areas because of not only its unique properties including high values of its mobility of charge carriers, thermal conductivity, mechanical strength, and specific surface areas but also the possibilities for a variety of applications such as electronic devices, batteries, solar energy conversion, and hydrogen storage. There are many methods for the preparation of graphene but each method has both advantages and disadvantages. Among them, the way to obtain graphene from graphite oxide (GO) by the reduction has been used because GO can be easily exfoliated into single layers by mild sonication. GO can be reduced by various methods, for example, the chemical, electrochemical, hydrothermal, thermal, and photocatalytic reduction.This study aims to prepare graphene and graphene-metal nanocomposites by photocatalytic reduction using polyoxometalates (POMs) which are homogeneous photocatalysts. Herein we prepared well-dispersed and highly reduced graphene oxide (r-GO) sheets loaded with metal nanoparticles in dimethylformamide (DMF) through the photocatalytic reduction of GO and metal precursors using phosphotungstate as a homogeneous photocatalyst. Graphene is a good substrate for the dispersion of metal nanoparticles because of its high surface area and good electron storage property. With phosphotungstates and UV light irradiation, both GO and metal ions can be successfully reduced to form the nanocomposites of Ag, Au, and Pd/r-GO that could be obtained in a stable suspension in DMF or an isolated paper sheet. Various spectroscopic characterizations of r-GO confirmed that the chemical functional groups present on the initial GO were removed after the photoreduction. Furthermore, metal nanoparticles were successfully deposited on r-GO with their size ranging from a few nm to 30 nm. This photochemical method is simple and environmentally benign and can be developed into a new procedure for the preparation of graphene loaded with a variety of metal nanoparticles