卤素离子对TiO_2薄膜光致亲水性的影响

Effect of Halides on Photo-induced Hydrophilicity over TiO_2 Films

将卤化钾盐KX(X=I、Br、Cl、F)分别引入至TiO2溶胶中,利用提拉法在载玻片上制得含有卤素离子的TiO2-X薄膜样片,通过测试样片紫外光照下水滴接触角的变化,考察了不同浓度的KI以及不同卤素离子对TiO2薄膜光致亲水性能的影响,并通过测试光照后的亲水薄膜样片暗处放置不同时间后接触角的变化,比较了含TiO2-I和TiO2-F薄膜样片亲水性能的持久性.结果表明,适量的KI有助于提高TiO2薄膜的光致亲水性,当TiO2溶胶中KI浓度为1.0×10-5mol·L-1时,其所制得TiO2薄膜的光致亲水性最好,继续增大KI浓度时,薄膜的光致亲水性逐步下降,当KI浓度达1.0×10-2mol·L-1时,其光致亲水性较纯TiO2薄膜差;同时,适量的KBr、KCl加入也有助于提高TiO2薄膜的光致亲水性,且随KI>KBr>KCl的顺序逐渐减弱,但KF的加入降低了薄膜的光致亲水性;另外,卤素离子的加入还有助于提高TiO2薄膜亲水性能的持久性,且KF>KI.分析认为,卤素离子对TiO2薄膜光致亲水性的影响与其给电子或捕获光致电子作用有关,并提出了其作用模型,而卤素离子与亲水基团(羟基)的氢键作用是使KX-TiO2薄膜能够延长亲水性时间的原因.

A series of TiO2-X films doped with different halides X^-（I^-, Br^-, Cl^-, and F^-） coated on the slide was prepared by dip-coating in the TiO2 sol into which potassium halide （including KI, KBr, KCl and KF） was introduced. The photo-induced hydrophilicity of TiO2-I films with different contents I^- was investigated by testing the change of water contact angle on film＇s surface with UV light irradiation time, so was the changes in photoinduced hydrophilicity of TiO2 films containing different halides. Then, the durability of the TiO2-X films was investigated by testing the change of water contact angle with dark storage time. Firstly, this result shows that the photoinduced hydrophilic property of TiO2 films could be enhanced by introducing a little KI into TiO2 sol, at the best with KI content of 1.0×10^-5mol·L^-1. However, with the further increase of KI, the photo-induced hydrophilic property of TiO2-I films would decrease, and even worse than that of pure TiO2 films when the KI contents is 1.0×10^-2mol·L^-1. Secondly, introducing KBr and KC1 of 1.0×10^-5mol·L^-1 into TiO2 sol could also enhance the photoinduced hydrophilicity of TiO2 films in an order of KI〉KBr〉KC1, but introducing KF decreased that of TiO2 films. Finally, introducing KX （KI and KF） could increase durability of hydrophilicity of TiO2 films under dark storage condition, and KF shows a better effect than KI. Based on these results, it is suggested that the halides act as electron donors or scavengers to affect the photo-induced hydrophility of TiO2 films, and the mechanisms of photo-induced hydrophilicity of TiO2-X films is proposed. However, the higher durability of hydrophilicity of TiO2-X films compared with pure TiO2 films may be due to a great stability of hydrophilicity site Ti-OH, which is caused by the strong binding action （hydron bond） between Ti-X and Ti-OH.