The role of preparation conditions in sol-gel methods on the synthesis of nanostructured photocatalytic films for water treatment

Synthesis of high performance titania photocatalytic films with good structural integrity is an important aspect in the design of high-efficiency photocatalytic reactors for water purification. One aspect of this dissertation deals with employing new approaches based on template-assisted Degussa P25 TiO2 powder modified sol gel processes for the synthesis of tailor-designed porous TiO2-P25 composite films with good structural integrity for water purification. A relatively low Degussa P25 loading (i.e., 10 g/L in the sol) is employed, which can avoid crack formation in the films. High porosity induced by the combined effect of template such as polyethylene glycol (PEG 2000) or polyoxyethylene (20) sorbitan monolaurate (Tween 20) with Degussa P25 can be beneficial to the exposure of the maximum number of high active Degussa P25 nanocrystallites in the inner layers to the solid-liquid interface. Moreover, the formation of P25 associated larger pores (i.e., macropores or larger mesopores) is beneficial to fast mass transfer of the treated contaminants in the larger pore channels. As a result, the enhancement in photocatalytic activity induced by low loading P25 is high. For the TiO2-P25 composite films prepared by a PEG-assisted P25 modified sol gel method (i.e., PPMSGF-PEG), the optimum calcination temperature is 500°C under which improved BET surface area/porosity and a bimodal macro-mesoporous structure can be formed. For mesoporous TiO2-P25 composite films prepared by a Tween 20-assisted P25 powder modified sol gel method, the optimum Tween 20 loading is 50% (v/v) in the sol under which high BET surface area (74 m2/g)/porosity (50.6%), bimodal mesoporous structure and larger film thickness can be obtained. On the other hand, the pore structure of photocatalytic films prepared by a P25 powder modified sol gel method (i.e., PPMSGFs) and in the absence of templates can be improved and the amount of surface foreign metal ions (i.e., Cr3+) diffused from the stainless steel support during heat treatment can be decreased by increasing P25 loading from 0 to 50g/L in the sol or decreasing calcination temperature from 600 to 500-400°C. However, crack formation cannot be avoided for the PPMSGFs with high P25 loading (i.e., 50 g/L in the sol) in this study.; Another aspect of this dissertation is to address some challenging issues in the formation of unique structures of TiO2 films using various sol gel methods without Degussa P25 TiO2 nanoparticles addition. By decreasing calcination temperature from 600 to 500°C, a crack free and thick TiO2 film with optimum film thickness (10 microm) as well as low porosity (∼5%) and narrow pore size distribution (2-10 nm) was successfully prepared. Moreover, the macro-mesoporous texture of thick TiO2 films without crack formation was obtained by optimizing the PEG 2000 loading in the sol (i.e., 20 g/L PEG 2000). Tween 20 was found to be an effective template in a non-acidic sol gel system. Optimization of Tween 20 loading (i.e., Tween 20: final sol = 50%, (v/v) in the sol) resulted in the formation of relatively ordered mesoporous structure of TiO 2 films with anatase nanocrystallites of ultrafine size (∼7 nm), high BET surface area (∼120 m2/g) and high pore volume (∼0.155 cm3/g). The advantages of the above unique structures of the as-prepared TiO2 films in the application of various water purification systems are emphasized.