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 ∼5 nm and large mesopore size of ∼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.