Effect of metal loading on photo-induced hydrophilocity of titanium dioxide thin films

Abstract

Titanium dioxide sol was synthesized using a sol-gel method. Various amount of silver, tungsten, copper, or molybdenum precursor solution were added to titanium dioxide sol to produce Ag-, W-, Cu-, or Mo-titanium dioxide sol. Then the modified titanium dioxide sol was coated on glass plates using a dip-coating technique to form the thin films. The as-prepared films were calcined at 350°C for two hours. The hydrophilicity of the thin films was evaluated by measuring the contact angle of water droplet on the film surface under UV irradiation. Addition of silver or tungsten to titanium dioxide enhanced hydrophilicities of the mixed oxide films. titanium dioxide film containing 3.0-5.0 mol% silver or 1.0-1.5 mol% tungsten not only possessed the best hydrophilic properties but also improved their abilities to retain hydrophilicity after removal of UV irradiation. This was attributed to silver and tungsten inhibiting the recombination of photo-generated electrons and holes, which agreed with the results from photoluminescence spectra. Addition of copper (0.1-5.0 mol%) or molybdenum (0.1-1.0 mol%) to titanium dioxide did not improve the hydrophilicity of the thin films because the photo-generated electrons were captured by metal oxide instead of creating surface oxygen vacancies on titanium dioxide surface. Furthermore, neither CuO nor MoO3 possessed hydrophilicity. An increase in the content of copper or molybdenum in titanium dioxide worsened the hydrophilic property of the thin film.