The Preparation Of Titanium-based Films And Their Electrophotocatalytic Performance

Photocatalysis has many merits in the terms of the removal ofharmful organic compounds, wastewater treatment and cleanup of pollutedair. This technology has been dramatically growing over the last decades.In recent years, TiO₂as an efficient photocatalysis has gained muchattention for its advantages of nontoxicity, photostability, andbiocompatibility as a highly efficient and promising photocatalyst.Generally, the degradation of organic pollutants is carried out insuspensions mediated by powder TiO₂. But in practical applications, thephotoactive flm is more viable due to its easy separation recovery andsimple post-treatment process. As for photoactive coating layer, largesurface area, sufficient mechanical/thermal stability and good adhesion to the substrates are the basic requirements.In this paper, we devote to search new methods to enhance theefficiency for photocatalytic reaction as well as to fabricate visible-lightresponse TiO₂films based on visible-light induced nanovoid-structuredTiO₂materials or iodine-doped TiO₂nanocrystals of the degradation ofpollutants. The main results and conclusions are summarized as follows:1) A visible-light response iodine-encapulated TiO₂film (I₂-TiO₂film)was prepared by packing the (I₂)n-encapsulated nanovoid-structured TiO₂particles and TiO₂nanocrystals (TNCs) via a doctor-blade method. Thevisible-reduced photocatalytic efficiency of the as prepared I₂-TiO₂filmwas measured by monitoring the decomposition of rhodamine B (RhB)Alizarin Red S (AR), fluorescein sodium (Flu) and2,4-dichlorophenol(2,4-DCP). The results showed that the degradation rate of the I₂-TiO₂filmwas significantly higher than pure TiO₂film. The improved photocatalyticperformance can be attributed to the present of (I₂)nencapsulated in TiO₂and work as photosensitizer to enlarge the spectral response and enhancethe visible-light utilization. Furthermore, the microparticles(I₂-TiO₂)/nanocrystals (TNCs) mixed structure, in which the I₂-TiO₂miroparticle worked as light scatterers, could be recognized as anotherfactor leading to an improved of light utilization of the film.2) A corbon-encapulated TiO₂film (C-TiO₂film) was prepared bypacing the corbon-encapulated TiO₂particles synthesized via sol-gel route using glucose as carbon source. The as-prepared films were characterizedby SEM, XRD, and diffuse reflectance spectra. With the analysis of EDSand XPS measurements we deduced that the carbon was encapsulated inthe nanocavities of TiO₂particles rather than doped in the lattice of it. Thedegradation efficiency of RhB, AR, Flu, and2,4-DCP under visible-lightirradiation was investigated. Compared with pure TiO₂film, the C-TiO₂film showed a higher photoreaction activity, which can be explained bythe banding shift causing by carbon modifying.3) The visible-light absorbing I₂-TiO₂and C-TiO₂film electrodeswere fabricated and studied as film electrodes for theirphotoelectrochemical and photoelectrocatalytic (PEC) properties. Thephotoelectrochemical property was evaluated by the incidentphoto-to-current conversion efficiency, electrochemical impedancespectroscopy and Mott-Schottky analysis data. The results showed thatI₂-TiO₂and C-TiO₂films exhibited stronger absorption in the400-550nmrange, lower electron transfer resistance and more negative fat bandpotentials comparing with pure TiO₂film. At a bias potential of0.5V, thevisible-light-induced PEC degradation ratios of RhB and tetracycline onI₂-TiO₂film or C-TiO₂film electrodes were significantly higher that onpure TiO₂electrode.4) An iodine-doped TiO₂nanocrystals film (I-TiO₂film) wasprepared and used as photocatalysis in Flu-sensitiezed and eosin Y (EO)-sensitized degradation of RhB under visible-light illumination. Thedegradation results showed that when Flu or EO was introduced to theI-TiO₂film/RhB system, the degradation ratio of RhB was significantlyenhanced, with an eight-fold or five-fold improvement compared with thatin the I-TiO₂film/RhB system free of sensitizer. In this degradationsystem the advantages of I-doping, inherent film characteristic andsynergistic degradation effect of binary dyes have been simultaneouslyachieved. This study could provide a feasible industrial route to designinghigh-performance visible light photocatalyst system.