High transmittance and superhydrophilicity of porous TiO2/SiO2 bi-layer films without UV irradiation

In order to obtain the TiO2 films with high transmittance and superhydrophilicity without UV irradiation, porous TiO2/SiO2 bi-layer films were prepared by spin coated SiO2 sol and TiO2 sol including polyethylene glycol 2000 (PEG 2000) onto glass and subsequent calcination at 550 °C. Meanwhile, factors that affect the TiO2/SiO2 bi-layer films transmittance and superhydrophilicity were investigated in details by observing their surface morphologies and measuring their water contact angles (WCAs), spreading time and transmittances. The results indicated that the as-prepared TiO2/SiO2 bi-layer film showed superhydrophilicity without UV irradiation when 0.5 wt.% PEG 2000 was added in TiO2 sol. At the same time, its maximum transmittance was as high as 92.3%. The spreading time was only about 0.16 s. More importantly, the resultant film had an excellent stability of the superhydrophilic property.