A comparative study on physicochemical properties and photocatalytic behavior of macroporous TiO2-P25 composite films and macroporous TiO2 films coated on stainless steel substrate Original Research Article

Two types of photocatalytic films, macroporous TiO2-P25 (Degussa) composite films (PPMSGF-PEG) and macroporous TiO2 films (TiO2-PEG), have been synthesized by a P25-PEG modified sol–gel method and a PEG modified sol–gel method, respectively. The physicochemical properties, including thermal behavior, surface morphology, crystallinity, crystal size, specific surface area (BET), pore volume and adhesion on the stainless steel substrate, of the two types of films were investigated by TGA, SEM, XRD, Raman spectroscopy, HRTEM, N2 adsorption and the tape test. The photocatalytic activities of the films were compared using 4-chlorobenzoic acid (4-CBA) as a model organic contaminant in water. It was found that adding 10 g/L P25 in the sol can improve not only the amount of crystalline material immobilized on the support, but also the BET surface area and pore volume of the films calcined at temperatures between 500 and 600 °C. N2 adsorption results suggested that the enhanced BET surface area and pore volume were due to the formation of large pores induced by the presence of P25 powders, which could help retain a relatively high pore volume during calcination at higher temperatures. The results on photocatalytic degradation of 4-CBA showed that the increase in photocatalytic activity caused by P25 powders reached maximum for PPMSGF-PEG calcined at 500 °C, compared with that of TiO2-PEG film. The tape test showed that adding 10 g/L P25 in the sol did not affect the critical calcination temperature (i.e., 500 °C) at or above which excellent adhesion between the films and the stainless steel substrate can be maintained. This study proves that optimizing calcination temperature is still an important strategy for the preparation of macroporous TiO2-P25 composite films with enhanced photocatalytic activity and excellent adhesion on the stainless steel substrate.