Bimodal mesoporous TiO2-P25 composite thick films with high photocatalytic activity and improved structural integrity

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 similar to 5 nm and large mesopore size of similar to 34 nm. 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. (C) 2007 Elsevier B.V. All rights reserved.