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

• In-depth understanding of synthesis of rGO–TiO 2 composites by photoreduction. • Variables of TiO 2 sources, irradiation time, light power were investigated. • Interaction of rGO and TiO 2 surface by XPS, Raman spectroscopies. • Experimental data analyzed by statistical models. • Provide insights for improving the design and preparation of rGO–TiO 2 composite. In UV-assisted photoreduction of graphene oxide (GO) using TiO 2 , TiO 2 supplies photogenerated electrons to reduce GO, which exhibits enhanced electrical conductivity, and induce a chemical interaction between TiO 2 and reduced-GO (rGO) for improved charge separation. Here, we investigated the photosynthesis of the TiO 2 –rGO composite with varying the UV irradiation time, TiO 2 source (TiO 2 -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 TiO 2 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 TiO 2 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 TiO 2 source had the highest impacts on the final products.