Photocatalytic application of graphene oxide–ZnO nanocomposite for the reduction of methylene blue dye

The graphene oxide (GO) and GO–zinc oxide (GO–ZnO) nanocomposite were prepared using simplified techniques with modified Hummer’s and solvothermal methods for photocatalytic application. In a comparative study, the optimized geometries, binding energies, electronic properties, non-linear optical properties and density of states (DOS) of GO–ZnO were calculated using density functional theory calculations with the B3LYP method and 6-31G (d,p) and LanL2DZ basis sets to examine the binding site of a methylene blue (MB) dye systematically. The result of natural bond orbital analysis revealed the effective charge transfer and also explained the mechanism and efficiency of the photocatalytic activity of GO–ZnO. DOS supported the strong interaction of MB with GO–ZnO leading to the degradation of the MB dye. The theoretical results obtained depict the existence of n → σ*, n→ n* and σ → σ* interactions, improved charge transfer, and reduced band gap which establish the use of GO–ZnO in visible light photocatalysis. Characterization methods such as x-ray diffraction (XRD), Fourier transform infrared (FTIR) and ultraviolet (UV) analysis were carried out to support our theoretical results. The XRD results confirmed the particle size of 21 nm with inter-layer spacing of 0.87 nm. FTIR spectroscopy indicated the characteristic bands related to the elements in GO–ZnO. The higher electrical conductivity was studied using UV–Vis spectral analysis. The calculated results show good agreement with experimental observations which reveal that the GO–ZnO nanocomposite has good photocatalytic behavior.