Improving the intrinsic properties of rGO sheets by S-doping and the effects of rGO improvements on the photocatalytic performance of Cu3Se2/rGO nanocomposites

The effects of S-doping on intrinsic properties of graphene oxide (GO) sheets such as interlayer spacing, reduction level, and electrical resistance and the influence of these properties on the photocatalytic performance of rGO/Cu₃Se₂ nanocomposites were investigated. A simple chemical method was used to synthesize S-doped GO sheets and a cost-effective co-precipitation method was used to decorate of the NPs on S-doped GO (as S-doped GO/NPs nanocomposites) and undoped GO (as undoped GO/NPs nanocomposites) sheets. X-ray diffraction (XRD) patterns of the products indicated that GO sheets were changed into reduced GO (rGO) sheets during the synthesis process. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images showed more exfoliation for the S-doped rGO sheets in comparison to the undoped rGO. X-ray photoelectron spectroscopy (XPS) indicated that S-doping caused an improve reduction level of rGO. UV–vis results revealed that S-doped rGO/NPs nanocomposites had a band-gap value around 2.2 eV that was bigger than the band-gap value of the undoped rGO/NPs that was around 1.9 eV. Room temperature photoluminescence (PL) results indicated that, the electron-hole recombination rate of S-doped rGO/NPs nanocomposites was lower than the undoped rGO/NPs nanocomposites. The photocatalytic activity under visible light irradiation for degradation of methylene blue (MB) dye showed a significant enhancement photocatalytic performance for S-doped rGO/NPs nanocomposites in comparison to the photocatalytic activity of the undoped rGO/NPs nanocomposites. Brunauer–Emmett–Teller (BET) calculation indicated a specific surface area of 251.6 and 220.7 m² g⁻¹ for the S-doped and undoped rGO/NPs nanocomposites, respectively. In addition, photoresponse measurements under visible light source irradiation indicated that, the electrical conductivity of rGO as an intrinsic property of the rGO sheets was increased by S-doping. Finally, according to valence band (VB) edge spectroscopy results of the samples, it was understood that a type-II heterostructure was formed by S-doped rGO/NPs with pristine NPs that was another important factor for the enhancement photocatalytic performance of this sample.