In-depth understanding of the photoreduction of graphene oxide to reduced-graphene oxide on TiO2 surface: Statistical analysis of X-ray photoelectron and Raman spectroscopy data

Abstract

In UV-assisted photoreduction of graphene oxide (GO) using TiO2, TiO2 supplies photogenerated electrons to reduce GO, which exhibits enhanced electrical conductivity, and induce a chemical interaction between TiO2 and reduced-GO (rGO) for improved charge separation. Here, we investigated the photosynthesis of the TiO2–rGO composite with varying the UV irradiation time, TiO2 source (TiO2-D or –HT, commonly employed in dye-sensitized solar cells), and light power. The final products were characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, and field-emission scanning electron microscopy. Most importantly, the chemical interaction between the rGO matrix and TiO2 was confirmed by X-ray photoelectron spectroscopy (XPS), whereas the carbon defects were studied by Raman spectroscopy. As expected, the chemical interaction between the rGO matrix and TiO2 was confirmed by the formation of Ti–O–C and Ti–C bonds. Moreover, during UV irradiation, the concentration of carbon defects increased evenly, implying that the photodegradation occurred simultaneously with the photoreduction of GO. The XPS and Raman data were further subjected to statistical analyses, including principal component analysis, multivariate linear regression and analysis of variance (ANOVA), and ANOVA–simultaneous component analysis. The results indicated that the irradiation time and TiO2 source had the highest impacts on the final products.