Effect of oxidation degree on photoactivity, physicochemical properties and oxidative potential changes of graphene-based materials under visible light irradiation

Graphene-based materials are subject to photochemical process when releasing into the environment. In this study, three kinds of graphene-based materials, graphene oxide (GO), soot and graphene (G), were selected to investigate their photoinduced changes of properties and the corresponding reasons. GO underwent reduction-dominant disproportionation, resulting in less oxygen-containing function groups (OFGs) and higher percentage of carbon-centered persistent free radicals (PFRs). Different kinds of soot particles all experienced self-oxidation, expressed as more OFGs, defects and carbon-centered PFRs adjacent to oxygen atom. Oxidative potential (OP) tested by DTT activity showed a decrease in GO but an increase in soot, agreeing with their changes of physicochemical properties. G remained almost unchanged in terms of both physicochemical properties and OP. Photoactivity measured by the productivity of photogenerated electron-hole pair and reactive oxygen species was responsible for above changes and correlated with the inner carbonaceous core. Carbonaceous core can behave as a photocatalyst to initiate photocatalytic reaction, and its oxidation degree (O/C ratio and OFGs content) determines the photoactivity. The relationship among the physicochemical properties, OP, photoactivity and inner microstructure found in this paper will help for better understanding of the environmental behavior and health effects of graphene-based materials.