Composition tuning in copper - oxide decorated reduced graphene oxide yields efficient photo- and reduction catalysts

A direct low-cost chemical reduction method is presented for the synthesis of the ternary Cu-Cu₂O-CuO system. In the presence of graphene oxide, the chemical reduction results in nanostructured copper and copper oxide decorated reduced graphene oxide structures. The presence of graphene oxide limits the conversion of copper to copper oxide and help the formation of the ternary system without the need for any controlled atmosphere. The composition of the ternary system could be changed by varying the amount of copper precursor used. X-ray diffraction studies and XPS analysis confirms the compositional variation in the synthesized nanocomposites. The dominant metallic phase converts to a mixture of metallic copper and Cu₂O dominant composition and then to a CuO dominant composition as the copper content increases in the sample. C1s peak shift in the XPS spectra indicates a strong interaction between graphene sheets and copper in copper rich compositions which has not been reported before. The composite nanostructures possess promising catalytic efficiency towards the visible light photodegradation as well as the hydride reduction reactions. The reduced graphene oxide-copper nanocomposites show improved photocatalytic activity with a rate constant value of 0.012 min^-1 compared to pure CuO which is having a rate constant value of 0.002 min^-1. The enhanced visible light assisted photodegradation is found to be due to the reduced graphene oxide assisted charge transfer and effective plasmonic coupling of the thermal and photonic energies over Cu₂O nanostructures. The electronic nature of the enhancement in photocatalytic activity was also confirmed by the quantitative assessment of hydroxyl radical formation using coumarin as a fluorescent probe during the visible light illumination reactions. The highest efficiency for the hydride reduction of para nitroaniline was exhibited by a different catalyst, CuRGO2 with a rate constant value of 0.269 min^-1. The Cu₂O-Cu-CuO ternary composition of CuRGO2 is instrumental in the high catalytic activity observed for this composite in the hydride reduction reaction. Thus, a rational design of heterostructured nanocatalyst for the visible light assisted degradation as well as the hydride reduction of organic pollutants can be achieved using the presented direct reduction synthesis.