Characterization of HF-catalyzed silica gels doped with Degussa P25 titanium dioxide

Abstract SiO2/TiO2 composites were synthesized by adding Degussa P25 TiO2 to a liquid sol that was catalyzed by HNO3 and HF acids. Various composites were synthesized by altering the mass loading of TiO2 and concentration of HF added to the liquid sol before gelation. The resulting materials were characterized by SEM, nitrogen adsorption–desorption, streaming potential, XRD, diffuse reflectance and TiO2 surface area analyses. Approximate characteristics include an isoelectric point of 3, TiO2 particle size of 30 nm, and a band gap energy of 3.2 eV. Small variations in these properties were noted for the different composites. Physical characteristics were largely affected by HF concentration and TiO2 loading. Nitrogen adsorption–desorption isotherms were type IV for all materials and exhibited trends of decreased pore volume with an increase in TiO2 loading and an increase in pore diameter with increased HF concentration. Surface areas of the composites ranged from 167 to 630 m2/g. Available TiO2 surface area of the composite was also dependent upon TiO2 loading and increased as the mass composition of TiO2 increased but was not largely affected by HF concentration.