The synergistic effect of graphitic N and pyrrolic N for the enhanced photocatalytic performance of nitrogen-doped graphene/TiO2 nanocomposites

The functionalization of graphene by nitrogen doping is an excellent method to modify the photocatalytic performance of graphene-based photocatalysts. However, the effect of N-bonding configurations (such as pyrrolic N, pyridinic N and graphitic N) on the photocatalytic performance of nitrogen-doped graphene/TiO2 composite (N-rGO/TiO2) has seldom been investigated. In this study, the different nitrogen sources (NH3, N2H4, and CO(NH2)(2)) have been used to prepare the N-rGO/TiO2 with the aim of obtaining different N-bonding configurations in graphene. It was found that when the NH3 and CO(NH2)(2) were used as the N-doping precursors, the resultant N-rGO/TiO2 photocatalysts mainly showed the pyrrolic N (>70%) and pyridinic N (>10%). As for the N2H4 precursor, the prepared N-rGO/TiO2(N2H4) primarily exhibited the pyrrolic N (ca. 63%) and graphitic N (ca. 37%) in graphene. The photocatalytic results indicated that all the N-rGO/TiO2 showed an obviously enhanced photocatalytic performance compared with the undoped rGO/TiO2. Moreover, the N-rGO/TiO2(N2H4) displayed the highest photocatalytic activity (k = 0.29 min(-1)), which is remarkably larger than that of TiO2 and rGO/TiO2 by a factor of 3.63 and 2.64, respectively. On the basis of the above results, a synergistic effect of graphitic N and pyrrolic N in graphene is proposed to account for the enhanced photocatalytic performance of N-rGO/TiO2(N2N4), namely, the graphitic-N doped graphene serves as an effective electron-transfer mediator for the photo-generated electrons while the pyrrolic-N doped graphene functions as the oxygen-reduction active site to rapidly promote the following interfacial catalytic reaction. It is quite believed that the synthetic effect of electron-transfer mediator and oxygen reduction activation site is a general and effective strategy for the design of high-performance photocatalytic materials. (C) 2015 Elsevier B.V. All rights reserved.