Investigations On Preparation Of Nanocrystalline TiO₂ Fibers And Their Photocatalytic Applications In Water Treatment

In this paper, nanocrystalline TiO2 fibers were prepared by centrifugal spinning of precursor of spinning solution which was synthesized by sol-gel method using TiCl4 as the titanium source, followed by heat treatment in water steam atmosphere. The preparation process of the spinning solution was optimized through orthogonal test. The structures of the precursor fibers and TiO2 fibers were characterized by FT-IR, DSC-TG, XRD, SEM, and TEM. The photocatalytic activities of TiO2 fibers were evaluated by decomposing the active brilliant red X-3B dye aqueous solution. The influencing factors of TiO2 fibers' photocatalytic activities, such as heat-treatment temperature, SiO2 doping amount, pH, UV light source, the X-3B solution concentration, were investigated. With the morphology advantages of the nanocrystalline TiO2 fibers, a practical photocatalytic reactor was designed and built, and the corresponding process for continuous water treatment was suggested. The results are described as follows:At first, orthogonal test was designed for optimizing the preparation process of precursor spinning solution. The TiO2 fibers prepared by our sol-gel method exhibit good continuity with diameters ranging between 5～10nm. Nano-sized pores richly distributed in the surface of the TiO2 fibers. It is indicated that SiO2-doping can evidently inhibit the grain growth and phase transformation of TiO2 fibers. The average size of the TiO2 grains within the un-doped and 15wt% SiO2-doped TiO2 fibers (heat-treated to 400℃) are 5nm and 10nm, respectively. Meanwhile, the temperature of anatase to rutile phase transformation is increased from 700℃for un-doped TiO2 fibers to more than 1000℃for 15wt% SiO2 doped fibers.Secondly, the results of photocatalytic experiments show that the TiO2 fibers doped with 15wt% SiO2 heat treated to 700℃have the best photocatalytic activity. The TiO2 fibers exhibited good photocatalytic activity of high efficiency on the degradation of X-3B solutions of different concentrations in condition of strong acid (pH=2) or strong alkaline (pH=14). One of the TiO2 fibers' virtues worthy of mentioning is that the fibers are reusable. A photocatalytic reactor and continuous water treatment process were designed attributed to the advantages of fiberous morphology of the nanocrystalline TiO2 fibers. The result of dynamic water treatment shows that the TiO2 fibers can endure water flow rate of 8L/min.Thirdly, a new method using potassium acetate as precursor to prepare TiO2 fibers has been developed, which is simple and economical. The TiO2 fibers prepared by the new method have higher strength than that prepared by the former sol-gel method. But the photocatalytic activities of the new fibers were decreased.