Using phosphoric acid as a catalyst to control the structures of mesoporous titanium dioxide materials

In order to control the surface area, pore size, pore volume as well as the phase structure of prepared mesoporous titanium dioxide materials in a template-free synthesis process, a catalyzed hydrolysis and polycondensation reactions of tetrabutyl titanate with phosphoric acid as a catalyst have been carried out. The main factors of the hydrolysis ratio (H2O/Ti molar ratio) and the phosphoric acid concentration were studied systematically. The calcined TiO2 materials were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and nitrogen adsorption/desorption measurements. A variety of TiO2 materials with different physicochemical properties could be effectively obtained by adjusting the synthesis conditions. X-ray powder diffraction patterns and nitrogen adsorption/desorption isotherms reveal that the afforded titanium dioxide materials have anatase structures and the mesoporous characteristics, respectively. TEM results indicate that the disordered wormhole-like mesostructure without discernible long-range order is formed by the agglomerization of TiO2 nanoparticles. The structures of the prepared materials could be controlled very well. The surface area varied from 41 m2/g to 294 m2/g, the average pore size from 5.4 nm to 9.4 nm, and the total pore volume from 0.056 cm3/g to 0.545 cm3/g. The phosphoric acid concentration is a dominating factor to control the pore size and its distribution. A unimodal or bimodal pore size distribution can result from changing the phosphoric acid concentration.