A visible-light responsive C, N and Ce co-doped TiO 2 mesoporous membrane has been synthesized via a weakly alkaline sol-gel route using P123 template. The co-doping of C, N and Ce resulted in a lowered band gap of 2.14 eV which improved the photocatalytic activity in visible light. The Ce-dopant was found to strengthen the Ti-O bond that stabilized the anatase phase as well as the assembled interconnected mesoporous structure during high temperature calcination. The stabilization of the crystal phase and pore structure resulted in a higher surface area, smaller and more uniform pore size in the membrane. The membrane exhibited a low cut-off molecular weight of 3300 Da and a water flux of 4.05 L m À2 h À1 per bar.
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 -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.
Hexagonal and cubic mesoporous TiO2 materials were synthesized via a sol-gel route modified by evaporation–induced self–assembly process with different templates. XRD and TEM results confirmed that the mesoporous films were highly organized. Furthermore, the hexagonal mesoporous TiO2 films were formed in the P123-templated films, whereas the cubic structure ones were found in the F127-templated films. Both the hexagonal and cubic mesoporous films showed photocatalytic activity in decomposing methyl orange solution under UV region, among which the cubic mesostructure presented superior potocatalytic activity because of larger surface area, more open framework and less obstructed diffusion paths of guest molecules.
The sol-gel technique is considered to be one of the most practical methods for producing ceramic membranes, and the properties of the sols could affect the microstructures of the desired products. Especially, optimized viscosity and a short gelation time can reduce the sol particles infiltrate into the pores of the support. So how to control the forming process of the gel is essential for fabricating the membranes. In this paper, we developed a kinetic equation of sol-gel transformation to study the relationships between viscosity and time of titanium sol systems by using N, N—Dimethylformamide (DMF) as solvent. Both the growth process of the sol particles and activation energy of the process were investigated according to the kinetic curves. The results indicate that the viscosity of sols decreases with the increment of R and temperature, but increases with rw, at the same time the gelation time decreases with rw, temperature and R. Furthermore, the growth of sol particles versus time accord with the NLG model, and the activation energy of gelation process decreased with R. When R changed from 2 to 6, the activation energy was decrease from 12.48KJ/mol to 9.35KJ/mol. According to the analysis of the results of the sol-gel transformation, a shorter gelation time could be obtained by increaseing the rw, R and the gelation’ temperature.
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