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Abstract: Bimodal mesoporous TiO2–P25 composite thick films with improved structural integrity (less crack formation) were successfully synthesized by employing an environmental friendly and highly viscous nonionic surfactant Tween 20 as a tri-functional template, which can simultaneously improve film texture, bimodal mesopore structure and structural integrity in the films. It was found that increasing Tween 20 loading from 10% to 50% (v/v) could simultaneously increase both volumes of small mesopore and secondary large mesopore. Degussa P25 nanoparticle can function as a kind of pore wall contributing to the formation of secondary large mesopore. Optimizing the loading of Tween 20 could result in optimum film thickness, even with only one dip-coating cycle. The final film at optimum Tween 20 loading (50%, v/v) exhibited large porosity (50.6%) and bimodal mesoporous size distribution with small mesopore size of ∼5nm and large mesopore size of ∼34nm. Compared with mono-modal mesoporous TiO2 film (no Degussa P25) at optimum preparation conditions (Tween 20, 50% (v/v), six dip-coating layers), the TiO2–P25 composite films prepared with the same Tween 20 loading (one dip-coating layer) or with 25% (v/v) Tween 20 loading (two dip-coating layers) demonstrated higher photocatalytic activities in the degradation of creatinine, an important human metabolite present in human urine. These results prove that bimodal mesoporous TiO2–P25 composite films have promising properties for photocatalytic water treatment. [Copyright &y& Elsevier]

Abstract: A transparent, relatively dense and thick TiO2 film with good mechanical properties and enhanced photocatalytic activity has been successfully immobilized on 304 stainless steel. The study included optimization of structural properties and film thickness. Experiments on the photocatalytic degradation of 4-chlorobenzoic acid (4-CBA) as a model organic contaminant showed that the photocatalytic activity of this kind of thick film can be significantly improved by decreasing calcination temperature (i.e. from 600 to 500°C), which is due to an increase in BET surface area and porosity, decrease in crystal size, and decrease in foreign metal diffusion from stainless steel support to the surface of the film. The observed apparent rate constant of TiO2-500 (500°C, two dip coating layers) was found to be approximately 5.2 times that of TiO2-600 (600°C, two dip coating layers). The results showed that increasing film thickness within a certain range (up to 10μm) could significantly improve the photocatalytic activity without causing crack formation for the thick TiO2-500 film (500°C). The optimum film thickness is 10μm (four dip coating cycles), under which the observed apparent rate constant of TiO2-500 is approximately 2.3 times higher than that of TiO2-500 with 2.5μm film thickness (one dip coating layer). Based on several advantages of TiO2-500 film (500°C, four dip coating layers), including high photocatalytic activity, absence of foreign metal ions at the film surface, optimum film thickness, good structural integrity, and excellent adhesion on the stainless steel support, this kind of sol–gel-derived thick film immobilized on stainless steel support is a promising potential photocatalyst for water treatment applications. [Copyright &y& Elsevier]

Abstract: The role of Degussa P-25 loading (0–100g/L) in the alkoxide sol was investigated for the synthesis of immobilized TiO2 photocatalytic films on 304 stainless steel using the P-25 powder-modified sol–gel method (PPMSGM). The structural properties of the films (PPMSGFs) obtained after gel drying and calcination at 600°C were examined using different materials characterization techniques including X-day diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The photocatalytic activities of films with good adherence to the stainless steel support were evaluated using 4-chlorobenzoic acid (4-CBA) as a model organic contaminant and UV-A radiation. The P-25 loading did not have a significant effect on the size of the crystallites in the films. However, increasing the P-25 loading in the sol resulted in an increase in (i) the amount of crystalline material retained on the support (i.e., for both anatase (101) and rutile (110) crystal phases); (ii) the number of grains (aggregates of P-25 particles and crystallites formed from the alkoxide sol); (iii) the number of pores in the film (in the range of 0–50g/L); and (iv) the number of microcracks on the surface of PPMSGFs. On the other hand, increasing the P-25 loading in the sol resulted in a decrease in the size of grains on the surface of PPMSGFs. XPS analysis revealed the presence of Cr3+, Mn3+ and Fe3+ on the surface of PPMSGFs as a result of diffusion of these species from the stainless steel support during film calcination at 600°C. The concentration of these foreign species on the film surface decreased with an increase in the P-25 loading in the sol. Increasing P-25 loading in the sol yielded films with higher photocatalytic activity but a concentration of 50g/L P-25 in the sol was found as the maximum for obtaining films with good adherence on the stainless steel support. Increase in the photocatalytic activity of the films with increasing P-25 loading in the sol was mainly attributed to the enhancement of the number of P-25 active sites exposed to the solution due to film morphology and surface characteristics and to the reduction in Cr3+ and Fe3+ concentrations on the surface of the films. [Copyright &y& Elsevier]