Regulating the Catalytic Function of Reduced Graphene Oxides Using Capping Agents for Metal-Free Catalysis

Reduced graphene oxide (rGO) functionalized with organic capping agents has gained increasing attention as a promising metal-free catalyst. To optimize the properties of rGO for target applications, comprehending the link between the catalytic function of rGO and the chemical and structural characteristics of capping agents is critical. Herein, we report a systematic study on the effect of capping agents on the catalytic function of rGO for redox reactions using nitrogen-containing surface modifiers with distinctly different chemical structures, such as poly(diallyldimethylammonium chloride), cetyltrimethylammonium chloride, and poly(allylamine hydrochloride), which have the capability to endow rGO with improved suspension stability, enhanced reactant adsorption, and modified electronic properties. Functionalized rGOs were facilely prepared by the reduction of graphene oxide with hydrazine in the presence of the capping agents. The results of model redox reactions, that is, 4-nitrophenol and ferricyanide reduction reactions, catalyzed by the functionalized rGOs corroborated that the way the capping agents functionalize rGO, which is highly correlated with their chemical structure, drastically influences the overall reaction kinetics, including induction time, reduction rate, total reaction time, and reaction order. This strongly suggests that the judicious selection of capping agents is crucial to fully harness the catalytic function of rGO and thus to design novel rGO-based non-metallic catalysts with controllable reaction kinetics.