In situ synthesis of N-CoMe2Pc/rGO nanocomposite with enhanced photocatalytic activity and stability in Cr(VI) reduction

Abstract

Graphene-based composites are widely used in the photocatalytic treatment of heavy-metal ions or dyes. In this study, we developed a facile in situ precipitation method for preparing a non-peripheral octamethyl-substituted cobalt(II)phthalocyanine (N-CoMe2Pc)/reduced graphene oxide (rGO) nanocomposite as an efficient photocatalyst. The physical and chemical properties of the nanocomposite were investigated by scanning electron microscopy, transmission electron microscopy, x-ray diffraction, and ultraviolet-visible, ultraviolet photoelectron, Fourier-transform infrared, Raman, and x-ray photoelectron spectroscopies. The results showed that the N-CoMe2Pc nanoparticles were immobilized on rGO nanosheets via π-πstacking interactions. The photocatalytic activity of the nanocomposite in the reduction of hexavalent chromium [Cr(VI), 10 mg/l] under visible-light irradiation was investigated. The Cr(VI) removal ratio reached 99.5% with a high photocatalytic rate of 0.0359 min-1, which is ten times faster than that achieved with pristine N-CoMe2Pc. The high removal efficiency is attributed to the following: (1) the number of active sites provided by nanodot-like N-CoMe2Pc is larger than that provided by bulk Pc, which can increase the production of photogenerated carriers, and (2) enhanced charge carrier separation resulting from intimate contact between N-CoMe2Pc nanodots and GO nanosheets. The N-CoMe2Pc/rGO also showed excellent stability and reusability. The Cr(VI) removal efficiency was 93.2% after eight photocatalytic test cycles.