Photocatalytic properties in aqueous solution of porous TiO2 - anatase films prepared by sol-gel process

Porous TiO2-anatase thin films were obtained by sol–gel method using dip-coating procedure onto glass-slides and silicon wafers in order to study the effect of the porous structure on the photocatalytic properties. 

Titania sols were synthesized using titanium isopropoxide (TISP) with two types of complexant molecules (acetyl-acetone (AcAc) or acetic acid (AcOH)) and different types of pore-generating agents as: Pluronic F127 (F127), cetyl trimethyl ammonium bromide (CTAB), sodium dodecyl sulfate (SDS), polyethylene glycol hexadecyl ether (Brij56, Brij58). The coatings were characterised by different techniques as grazing X-ray diffraction (GXRD), spectral ellipsometry, Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). Maximum thickness around 280 nm, and refractive index as low as 1.68 were obtained, indicating that the surfactants allow obtaining porous films. GXRD and TEM analysis confirm the presence of a porous structure but not ordered. TiO2 films obtained from AcAc or AcOH with Brij58 and F127 sols present specific surface areas between 28 and 68 m2/g. Photocatalytic activity was studied through the degradation of methyl orange in aqueous solution under UV light exposure. Methyl orange degradation increases with the film thickness up to a maximum value of 470 nm, beyond which the efficiency does not further increase. The photocatalytic activity depends on different parameters, such as porosity, film thickness and total surface exposed to illumination.