The mechanism of the reaction of graphite oxide to reduced graphene oxide under ultraviolet irradiation

Under ultraviolet (UV) irradiation, the formation and reduction mechanism of reduced graphene oxide (rGO) layers prepared from graphite oxide (GO) sheets have been investigated. The effects of hydroxyl free radicals (HO), hydroxide ions (OH−) or hydrazine molecules (N2H4) are considered. It has been demonstrated that the HO radicals, UV-induced from H2O2 molecules in aqueous solution, cannot reduce GO into rGO, but to some extent oxidize and damage the GO structure, simultaneously accompanied by a slight increase of acidity, possibly because of a release of H+ from H2O2 and GO during the reaction. The existence of OH− ions or N2H4 instead of H2O2 molecules enables GO sheets to be quickly reduced into rGO due to the effect of photo-induced electrons on the GO sheets. The electrons are photogenerated mainly from OH− or N2H4 in a GO aqueous dispersion. Because GO in diluted N2H4 aqueous solution can be photo-reduced almost completely within half an hour at room temperature, it is inferred that many more electrons are generated from N2H4 than from OH−.