Growth and photocatalytic behavior of transparent reduced GO-ZnO nanocomposite sheets

Reduced graphene oxide-zinc oxide (rGO-ZnO) nanocomposites were grown on solid substrates by rapid thermal treatment of Langmuir-Blodgett transferred GO-Zn composite sheets in oxygen ambient. The changes induced by uptake of Zn²⁺ ions and subsequent thermal treatment on surface morphology, micro-structure, composition and optical properties of composite sheets were investigated by atomic force microscopy, high resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectra (XPS), Fourier transform infrared (FT-IR) and Raman measurements. The morphological features of composites are practically independent of subphase Zn concentration and are largely determined by the temperature of rapid thermal treatment. FT-IR results indicate the presence of zinc carboxylate in composites and HR-TEM results confirm the formation of ZnO nanoparticles upon subsequent oxidation. XPS and Raman measurements show that rapid thermal treatment in oxygen ambient results in decrease of carbon-oxygen functional groups and increase in graphitic carbon content leading to the reduction of GO in the composites. The average optical transmittance of rGO-ZnO composites in the visible region is found to be ∼87%. Photocatalytic studies carried out on methylene blue (MB) overlayer coated rGO-ZnO composites show reduction in concentration of MB with increasing duration of UV irradiation. The transparent two-dimensional rGO-ZnO composite solid state structures thus facilitate efficient adsorption and degradation of MB molecules, without any composite aggregation.