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

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.

采用溶胶-凝胶法（sol-gel method）合成二氧化钛溶胶。向其中添加不同用量的银、钨、铜或钼前驱体溶液，制备得到掺银、掺钨、掺铜及掺钼二氧化钛溶胶。随后采用浸涂法（dip-coating technique）将改性后的二氧化钛溶胶涂覆于玻璃板上，得到初始薄膜；将该初生薄膜于350℃下煅烧2小时。通过测试紫外光照下薄膜表面的水接触角，评估该薄膜的亲水性能。向二氧化钛中掺入银或钨，可提升复合氧化物薄膜的亲水性能。其中，掺有3.0~5.0 mol%银或1.0~1.5 mol%钨的二氧化钛薄膜，不仅具备最优的亲水特性，还可在紫外辐照停止后更好地维持其亲水状态。该现象源于银和钨抑制了光生电子与空穴的复合，这一结论与光致发光光谱（photoluminescence spectra）的测试结果一致。向二氧化钛中添加0.1~5.0 mol%的铜或0.1~1.0 mol%的钼，则无法改善薄膜的亲水性能，原因在于光生电子会被金属氧化物捕获，而非在二氧化钛表面形成表面氧空位。此外，氧化铜（CuO）与三氧化钼（MoO3）本身均不具备亲水性能。且二氧化钛中铜或钼的掺杂含量越高，薄膜的亲水性能越差。