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

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-transforminfrared, Raman, and x-ray photoelectron spectroscopies. The results showed that the N–CoMe2Pc nanoparticles were immobilized on rGO nanosheets via π–π stacking 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.