ABSTRACT
This chapter encompasses a detailed overview of recent trends in the synthesis of graphene-transition metal-oxide-based nanocomposites and their applications for the photocatalytic degradation of pollutants. The comprehensive case study of the synthesis of reduced graphene oxide (rGO)-TiO2 nanocomposites for photocatalytic and sono-photocatalytic degradation of methomyl (carbamate group pesticide) has further thrown some more light on the topic.
Nanocomposites of transition metal oxides and graphene in the form of graphene oxide (GO) and rGO has gained lot of popularity because graphene can significantly enhance the photocatalytic activity of transition metal oxides. Graphene transition metal oxide nanocomposites mainly include composites viz. rGO/GO-TiO2, rGO/GO-ZnO, rGO/GO-Fe3O4, rGO/GO-CuO, rGO/GO-V2O5, rGO/GO-Co3O4, rGO/GO-MoO3, rGO/GO-ZrO2 etc. They can be synthesized by using various methods viz. hydrothermal/solvothermal method, sol-gel method, in-situ deposition/chemical method, etc. The size, morphology, and photocatalytic activity of the nanocomposite is dependent on the method adopted for the synthesis of the nanocomposite.
Graphene-transition metal-oxide-based nanocomposites have witnessed tremendous applications in wastewater treatment. These nanocomposites have successfully degraded many types of organic pollutants, such as dyes, pesticides, and pentachlorophenols. Previous research reports and the case study presented have clearly indicated that these nanocomposites possess high photocatalytic activity as compared to bare transition metal oxides under both UV and visible light. The key beneficial effect of using graphene-based nanocomposites includes the availability of active sites in the form of functional groups useful for anchoring transition metal oxides. Apart from this, graphene can also act as an electron sink and, hence, lower the charge carrier recombination.
