Low-temperature Preparation Of Visible Light Responsive TiO₂-SiO₂ Films And Their Applications In Photocatalytic Degradation

TiO₂ has emerged as the most significant semiconductor photocatalyst for its chemical stability,abundance,nontoxicity,and cost-effectiveness.However,its application is restricted since it has a wide band gap?3.2 eV?.It only shows photocatalytic activities under ultraviolet irradiation.There are many shortcomings in the practical application of TiO₂ powders,such as difficulty in recycling,necessary filteration in the follow-up and easy leakage into the environment.While the films can overcome these shortcomings,thus shows a large variety of practical applications.The TiO₂ films prepared by traditional physical or chemical methods need post high temperature annealing process for the crystallization of TiO₂ and adherence to the substrate,which are usually impractical for organic polymer substrates with poor thermal stability.Therefore,it is of great importance to prepare TiO₂ film with high photocatalytic efficiency in a low temperature.In order to get this kind of films on flexible substrate,we prepared TiO₂-SiO₂ sol by a sol-gel method and then prepared the film through a dip-coating technique,and subsequently put the film into hot-water to enable the crystallization of TiO₂ nanocrystals at low temperature.Finally,we obtained N-Fe co-doped TiO₂-Si O2 films.The adhesion property of film to substrate was improved by adding coagulator N3390.The main contents include two parts:?1?N-Fe co-doped anatase nanocrystals in sol-gel derived TiO₂-Si O2 micro-and mesoporous films?denoted as N-xFe-TiO₂?are synthesized by hot-water treatment at a low temperature?<100 °C?and can be formed on various kinds of substrates including organic polymers?PET,PC?with poor heat resistance.XRD and TEM measurements show anatase nanocrystals with size of 6-10 nm homogeneously dispersed in film matrices.The thin film surface and cross-section morphology were observed by SEM and AFM,conbined with FT-IR analysis,we can judge what reactions and changes have taken place over time during the process of hot water treatment result in nano porous anatase TiO₂ film.XPS proves successful codoping of N and Fe ions into the TiO₂ lattice.UV–vis diffuse reflectance spectra certify doping indeed decreased the band gap energy of doping films?Eg=3.13 eV,3.09 eV and 2.96 eV for the TiO₂,N-TiO₂ and N-1Fe-TiO₂,respectively?.Nitrogen adsorption-desorption measurements display that the N-Fe codoped films possess much higher specific surface area,specific pore volume and mean pore size compared with the no-doped sample TiO₂.The low-temperature hot-water treatment process provides an opportunity to integrate the catalyst with thermal labile substrates such as organic polymer for more practical applications.The films show highly efficient and stable photodegradation activity for rhodamine B?RhB?aqueous solution under visible light.Among them,the films doped with low concentration of Fe?x=0⁰.1%?demonstrate relatively fast decoloration of RhB,and the deethylation process is found to dominate over the cleavage of the chromophore structure during this photodegradation process;while the mineralization efficiency reaches the maximum of ⁶1% for the sample N-xFe-TiO₂?x=1?.We put forward a mechanism to explain the phenomenon of the N-xFe-TiO₂ film degradation Rh B solution under visible light irradiation.It was found that the doped Fe3+ changed not only the photodegradation rate but also the mechanistic pathways of the RhB degradation.?2?The adhesion of films was improved by adding N3390 and N3390-N-0.05Fe-TiO₂ film with good transmittance in the visible light range.The N3390-N-0.05Fe-TiO₂ film has lower photocatalytic efficiency of RhB solution compare to N-0.05Fe-TiO₂ film in visible light,but also maintained a certain catalytic properties.The N3390-N-0.05Fe-TiO₂ film has good photodegradation efficiency to formaldehyde and acetone gas under 365 nm UV light irradiation.The appearance and adhesion of added N3390 film took a step toward the practical application.