Carbon

A series of reduced graphene oxide (RGO) colloids with different amounts of surface charges was prepared. The change in surface charge at different pH values was detected by zeta potential measurement, and the evolution of oxygen-containing functional groups attached to the RGOs was analysed by Fourier-transform infrared spectroscopy and ultraviolet-visible absorption spectroscopy. Results showed that the edge phenolic hydroxyl and carboxyl groups made more contributions to the negative surface charge compared with the basal-plane hydroxyl and epoxy groups. Electrical impedance spectroscopy results proved that the surface charge of RGOs significantly affected their electrochemical properties. Furthermore, GO and RGOs (graphene oxide materials) were also used to construct electrochemical sensors for quantitive measurement of Cu2+ by differential pulse anodic stripping voltammetry. The results revealed that the increase in negative surface charge on RGO enhanced its electrocatalytic activity for Cu2+ reduction. Thus, considering that studies on the properties of graphene oxide materials can be simplified by the surface charge, its analysis is an important means of material characterisation. (C) 2013 Elsevier Ltd. All rights reserved.A series of reduced graphene oxide (RGO) colloids with different amounts of surface charges was prepared. The change in surface charge at different pH values was detected by zeta potential measurement, and the evolution of oxygen-containing functional groups attached to the RGOs was analysed by Fourier-transform infrared spectroscopy and ultraviolet-visible absorption spectroscopy. Results showed that the edge phenolic hydroxyl and carboxyl groups made more contributions to the negative surface charge compared with the basal-plane hydroxyl and epoxy groups. Electrical impedance spectroscopy results proved that the surface charge of RGOs significantly affected their electrochemical properties. Furthermore, GO and RGOs (graphene oxide materials) were also used to construct electrochemical sensors for quantitive measurement of Cu2+ by differential pulse anodic stripping voltammetry. The results revealed that the increase in negative surface charge on RGO enhanced its electrocatalytic activity for Cu2+ reduction. Thus, considering that studies on the properties of graphene oxide materials can be simplified by the surface charge, its analysis is an important means of material characterisation. (C) 2013 Elsevier Ltd. All rights reserved