Concurrent and dual N-doping of graphene/ZnO nanocomposites for enhanced Cr(vi) photoreduction activity under visible-light irradiation

Simultaneous and dual N-doping of two components in reduced graphene oxide/ZnO nanocomposites were successfully achieved by thermally annealing a GO/Zn(HCO₃)₂ precursor in an NH₃ atmosphere. In this facile preparative procedure, NH₃ was used not only as the reagent for in situ reduction of GO but also as the source for N-doping. Detailed characterizations showed that the nitrogen element was successfully and simultaneously incorporated into the crystal lattice of ZnO and graphene phases in the composites and the formation of oxygen vacancies was also achieved. The photocatalytic tests indicated that N-doping of graphene/ZnO (NG/NZO) nanocomposites exhibited the higher Cr(vi) photoreduction activity than graphene/ZnO, virgin N-doped ZnO (NZO) and the sample prepared via simple physically mixing. The mechanistic study demonstrated that the remarkable photocatalytic activity of NG/NZO photocatalysts was due to the synergistic effect of simultaneously N-doping two phases in the composites and the existence of oxygen vacancies, and mainly included the increased electrical conductivity of N-doped graphene (NG), the expansion of visible light harvesting capability of NZO and the effective separation of electron-hole pairs of the oxygen vacancies.