Preparation of TiO2–carbon surface composites with high photoactivity by supercritical pretreatment and sol–gel processing

TiO2–carbon surface (TCS) composites were prepared by pretreatment of a sealing substrate in supercritical carbon dioxide using paraffin as a plugging agent, and sol–gel processing using tetrabutyl orthotitanate as a precursor. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectrum (XPS), optical absorption spectroscopy and nitrogen absorption. The photoactivity of TCS was checked by monitoring the decomposition of methylene blue (MB) in aqueous solution under UV irradiation. The results indicated that compared with TC prepared only by the sol–gel method, the small nanosize TiO2 particles are well dispersed on carbon surface with large amount of micropores and high Eg values, meanwhile TCS have high Ti3+ concentration due to supercritical pretreatment providing a amount of carbon on the composite surface with interfacial energy effects, which controls the growth of TiO2 nanoparticles, baffles the agglomeration of TiO2 nanoparticles and easily produces Ti3+ ions. These are reasons why TCS has a higher efficiency of decomposing MB than TiO2–carbon (TC) composites and pure TiO2. Additional, it is also attributed to the fact that TCS produce a high concentration of organic compounds near TiO2 in comparison with TC and pure TiO2, because their surface area are greater than that of TC and pure TiO2.