Preparation, Characterization And Photocatalytic Properties Of Nanometer Mesoporous Anatase Titania Consecutive Fibers

As we all know, titania is a very promising photocatalyst used to degrade organic pollutants in wastewater. However, the conventional applications of titania such as nono-powders and supported catalysts have many drawbacks in practice, nono-powders shows high photocatalytic property but it is difficult to recycle, supported catalysts are likely to be degraded through sintering, attrition, etc, which make photocatalytic technique in wastewater application stagnant. Therefore, it is preferable to prepare self-constructed titania fibers with high surface areas and high contents of anatase, which can be free of the losing problems of nono-powders and the low efficiency of supported catalysts.In this paper, I will introduce a novel and facile technology based on sol-gel method to obtain Si-doped anatase TiO₂ fibers with abundant mesoporous structure, which possesses excellent thermal stability and crystal stability. It provides a bran-new way to solve the above problems availably for its advantages in morphology and specialty in endure current strike burthen. The main purpose of this thesis is to investigate the method of producing high quality Si-doped TiO₂ fibers cosmically and the primary applications in photocatalytic degradation of organic substances in wastewater, which will be discussed in three parts.In first part, the improved sol-gel method was used to prepare the precursor of TiO₂ fibers with tetrabutyl titanate as the source of Ti and tetraethyl orthosilicate as the source of Si with the double protection of N₂ and chelat reagent, and the mechanism of preparing the precursor sol were investigated systematically. By orthogonal experiment we confirmed the optimum conditions for precursor sol preparation: n(Ti(OB)₄): n(C₆H₁₀O₃): n(H₂O): n(C₃H₈O)=1:0.4:1.5:16, circumfluent time is 60 min. Basing on the unique character of our own sol system, we designed a centrifugal spinning apparatus to obtain precursor fibers with single-filament lengths longer than 1 m and diameters in the range of 30-50 In second part, relative gentle environment was chosen to dry the precursor fibers, so that the destruction on fibers' structure can be avoided, the destruction could be caused by the stress focusing extremely during the drying if the environment is bad. Si-doped TiO₂ fibers were successfully prepared by one-step steam activation combined with stage-temperature-programmed technology. The natural reason for forming high-quality TiO₂ fibers was firstly made clear, which showed that the heating conditions took very important effects on the precursor fibers' transformation process and the obtained TiO₂ fibers' continuity and photocatalytic activity. The heat treatment under atmosphere caused the organics in the precursor fibers to be carbonized, inducing structural stress and resulting in the poor continuity and photocatalytic activity. However, the organics in the precursor fibers would remove in the form of molecule directly when that was under steam. The removal of the organics was a gradual and mild process, so the series of harmful effects of carbonization could be avoided perfectly, so that it was possible to fabricate high-strength continuous TiO₂ fibers with high photocatalytic activity by using proper heating program under steam.In third part, TG-DSC, XRD, FT-IR, UV-Vis-DRS, N₂ absorption-desorption, SEM were used to systematically study the effects of Si doping on fibers' thermal stability, crystal stability, surface morphology, photocatalytic activity, and primary discussed the effect mechanism of Si doping. On the one hand, Si doping can form Ti—O—Si bond, so that it can suppress the phase transformation of titania from anatase to rutile and forming quantum domino effect to improve the separation efficiency of photo-electrons and holes. On the other hand, Si doping can optimize fibers' surface morphology, and helps to improve their specific surface area and pore volume.The photocatalytic degradation of X-3B in aqueous solution was used as a probe reaction to evaluate their photocatalytic activities, using sunlight as natural lamp-house and high pressure mercury lamp as manpower lamp-house respectively. The results indicate that Si-doped TiO₂ fibers possess not only excellent UV photocatalytic activities, but solar photocatalytic activities equal to Degussa P25 nano-powders. The sample has the largest specific surface area, pore volume and the best photocatalytic activity when the molar ratio of Si/Ti is 0.15. Under optimum condition, 99.6% of X-3B was degraded after irradiated within 75 min under UV-light. A simple photocatalytic reactor of TiO₂ fibers was designed and used to continuously treat X-3B solution. In the case, 98.8% degradation ratio of X-3B and 76.5% degradation ratio for TOC were detected within 5 h solar irradiation. X-3B is photocatalytically degradated via decolorization and mineralization sequentially. Silica-doped TiO₂ fibers are a kind of novel functional materials in water treatment field, which possess high photocatalytic activity and are easy to be recycled.