Preparation And Characterization Of Mesoporous Titania Crystal Fibers For Water-treatment Functionalization And Its Photocatalytic Properties

Photocatalytic oxidation of n-type semiconductor using dissolved oxygen in water as O source, has already become a research focus in water treatment field in the last twenty years. However, the conventional nano-TiO2 suspended system has many inherent drawbacks, such as easy deactivation, easy agglomeration owned, difficult separation and low light utilization efficiency. The technology of mounting TiO2 on supports can solve the problem, but bring about low photo quantum efficiency and easy shedding. The above factors limit the application of photocatalytic technology.In this paper, Si-doped and pure TiO2 fibers were synthesized by two kinds of processes based on modified sol-gel method combined with dry spinning and steam-activated heat treatment, which provided a bran-new way to solve the above problems availably for its advantages in morphology and specialty in endure current strike burthen. The prepared samples were deeply investigated by XRD, SEM, FT-IR, DSC-TG, UV-Vis DRS, XPS and N2 adsorption-desorption et al. Combined with the photocatalytic experimental results, we discussed the effects of crystal structure, absorption characteristics and surface texture for the photoactivity. This paper was divided into three parts as follows:In the first section, Si-doped mesoporous TiO2 continuous fibers were prepared by improved sol-gel method using tetrabutyl titanate and tetraethyl orthosilicate as Ti and Si source followed by centrifugal spinning. The fibers with uniform diameters about 10-20μm were consisted of nanoparticles and abundant mesopores. The addition of silica was a crucial factor for obtaining long fibers because of the formation of Ti-O-Si networks. The crystal phase, crystal morphorlogy, surface area and pore structure were controlled by varying the contents of silica and heat treatment temperatures. It was found that the proper addition of Si could improve the surface texture and enhance the thermal stability and crystal stability. When Si/Ti molar ratio was 0.15, the product heated at 700℃retained the maximal surface area and pore volume of 127.7 m2·g-1 and 0.25 cm3·g-1 respectively. It displayed the highest photoactivity of all, and the degradation rate of X-3B in aqueous solution reached 99.6% after 75 min under UV irradiation. Also, the degradation rate and the mineralization rate of X-3B were 94.7% and 58.9% after 3 h under solar irradiation, respectively. In addition, the degradation rate was also more than 90% after 6 cycles. Furthermore, the results of bactericidal test showed that TiO2 fibers not only possess bactericidal properties under UV light but also antimicrobial properties in dark.In the second section, F, N-modified fibers were prepared, which were consisted of double-mesopore structure and surface hydroxyl groups, using 0.15STF-700 as raw material, HF and HNO3 as modifiers. And they exhibited high adsorption efficiency with removal of X-3B being over 84% through electrostatic force and ion exchange. Furthermore, collaborative photocatalysis between TiO2 and adsorbed pollutants, which resulted a substantial increase in UV-active, occurred and led to visible light response with the degradation rate of X-3B being 98% after 45 min.In the third section, TiO2 crystal fibers were prepared using tetrabutyl titanate as Ti source, polyvinylpyrrolidone (PVP) as template and acetic acid as stabilizer and chelating agent through a novel and facile sol-gel method. On the one hand, PVP could improve the viscosity of TiO2 gel to obtain the precursor fibers with uniform diameters about 40μm by dry spinning, while the apparent viscosity reached several Pa·S and the gel belonged to pseudoplastic fluid by rotational viscometer. On the other hand, PVP could lower phase transition temperature and produce abundant mesopores through the follow-up thermal decomposition, which was helpful for increasing surface area and pore volume. The unique stage-temperature-programmed technique, heat preservation at 500℃and up to 700℃, could suppress the growth of rutile particles and obtain mixed form of anatase and rutile with suitable proportion. The photocatalytic results showed that the fibers with mixed crystal exhibited high photocatalytic activity and the degradation rate of X-3B (50 mg·L-1) reached 95% after 120 min under UV irradiation.