Fabrication of mesoporous N-TiO₂ membrane and its spectral characteristics

Ceramic ultrafiltration membrane, pore size from 2 to 50nm, is of growing interest in separation and purification processes because of their higher chemical, thermal and mechanical stability compared to organic membranes. TiO₂ mesoporous membranes have gained tremendous popularity due to their photocatalytic activity and because they possess high water flux and chemical resistance. In recent years, visible-light-induced nitrogen-doped titanium dioxide (N-TiO₂) materials have been attracted extensive attention. We synthesized asymmetric N-TiO₂ membrane based on this material via sol-gel method, in which titanium tetrabutoxide was used as Ti-precursor and formamide as nitrogen resource. A a-alumina support with macropores was used and its diameter, thickness and pore size were 28.5 mm, 2.2 mm and 0.10μm, respectively. The alumina supports were pretreated using PVA to prevent permeation of sol into the supports. Sol was coated on this treated supports, and then formed gel under 60°C. The resulting membrane posseses a pore size of 4nm and its pure water permeability is 3.3L/(m²· h·bar). The influences of formamide on the microstructrue and the spectral characteristics were also analyzed by means of BET, UV-vis. As indicated by results, when the molar ratios of formamide and titanium terabutoxide were near 4, the materials had excellent visible light absorption, the absorption band was shifted to about 545nm and the band gap was reduced to 2.65eV. The band gap was 0.55eV less than that of pure TiO₂. The membrane has potential application in purifing of micro-polluted surface water under visible-light environment.