Reduced graphene oxide can activate the sunlight-induced photocatalytic effect of NiO nanowires

Nickel (II) oxalate dihydrate nanowires, synthesized in the presence of graphene oxide, were thermally decomposed into a composite of graphene oxide and nickel oxide (GO-NiO) nanowires, and the composite was then reduced into a composite of reduced graphene oxide and nickel oxide (rGO-NiO) nanowires. The structures were characterized by field emission scanning electron microscopy, X-ray diffractometry, and Fourier-transform infrared spectroscopy, showing the presence of graphene in the structure as well as the reduction of graphene oxide sheets existing in the structure into reduced graphene oxide sheets. UV-visible spectrophotometry showed that rGO could enhance the absorption of NiO nanowires, particularly in the visible region of light, and also could decrease their bandgap energy from 3.3 to 2.8 eV. Photoluminescence spectroscopy indicated that rGO could vanish the PL intensity of NiO nanowires, meaning that the rGO-NiO sample has a lower e-h recombination rate than that of the NiO sample. It was shown that although NiO nanowires had an insignificant photocatalytic effect, the incorporation of rGO could activate it, increasing its activity to nearly equal to that of the standard TiO2-P25 photocatalyst. Finally, we discussed the mechanism behind the enhancement of the photocatalytic activity. (C) 2018 Elsevier Ltd. All rights reserved.