Preparation Of TiO₂and Bi₂O₃Composite Thin Films And Their Surface Self-cleaning Properties

TiO₂thin films are the most popular self-cleaning materials due to its photocatalyticreactivity and photo-induced superhydrophilicity. However, low use of solar light and easyrecombination of photo-induced electrons and holes resulting to its low photocatalyticefficiency, limiting its practical application. In addition, another important limiting factor isthat the superhydrophilicity of TiO₂thin films rapidly vanishs if the UV light irradiation isremoved. Depending on that compounded semiconductors can improve the efficiency ofphotoquantum effectively, and the superhydrophilicity is influenced greatly by the surfacemicrostructures and hydroxyl groups, we designed to use the compounded semiconductorsand mesoporous SiO₂thin films to improve the photocatalytic efficiency andsuperhydrophilicity of TiO₂, respectively. A simple sol-gel/spin-coating method was used toprepare titanium/bismuth oxide composite films and mesoporous SiO₂/Bi₂O₃/TiO₂multilayered films. Self-cleaning properties of the films were evaluated, hoped to haveantifogging ability even in dark and more efficient antifogging and antifouling abilities underweak UV light irradiation.Using sol-gel method, multi-layered thin films and mixed thin films consist of Bi₂O₃andTiO₂were prepared on glass slides. The samples were characterized by XRD, SEM, UV-Vis,XPS and contact angle measurements. Methyl orange was used as a model pollutant toevaluate the photocatalytic property of the thin films, and the self-cleaning properties of thethin films was used the degradation of stearic acid to evaluate.The results showed that all thesamples keep a high transparency. Both multilayered thin films and mixed thin films canimprove the photocatalytic and photo-induced hydrophilicity of the TiO₂thin film. In themultilayered thin films, TiO₂had an anatase crystallite structure and Bi₂O₃possessed bothmonoclinic and tetragonal structures. Multilayered thin films had the highest photocatalyticactivity when Bi₂O₃is the upper layer. The photocatalytic activity of multilayered thin filmswere impacted by thickness of the films, the photocatalytic activity of the multilayered thinfilms increased with the increase in the film thickness, however, when the film thicknessreach a certain value, that is Bi₂O₃and TiO₂spin-coated for three times, respectively, thephotocatalytic activity decreased with the increase in the film thickness. Mixed thin filmsconsisted of Bi₂O₃and TiO₂. Bi₂O₃doping inhibited the growth of the TiO₂particles. All thethin films showed obvious photocatalytic activity for the degradation of methyl orange, andBi₂O₃/TiO₂multilayered thin films showed higher photocatalytic activity than Bi₂O₃-TiO₂mixed thin films, suggesting that the layering method is more effective to improve the photacataltyic activity of Bi₂O₃and TiO₂compounded semiconductors.To synthesize thin films with antifogging property in the absence of light irriadiation,mesoporous SiO₂/Bi₂O₃/TiO₂multilayered thin films were prepared on glass slides usingsol-gel/spin-coating method. The results suggested that the multilayered thin films kept themesoporous structure of SiO₂, performing superhydrophilicity and antifogging property in thedark. In addition, compared to Bi₂O₃/TiO₂double-layered thin films, the triple-layered thinfilms had a better photocatalytic activity and transparency. Other tests suggested thatmesoporous SiO₂/Bi₂O₃/TiO₂triple-layered thin films had good adhesion with substrate, aswell as could resist acid and alkali corrosion in the nature environment.