Preparation, Characterization And Photocatalytic Properties Of Nanocystal Self-Supported Continuous Titania Fibers

Nanotitania plays a crucial role in photocatalytic field because of its innocuity, high photocatalytic activity, high redox ability and high chemical stability. But, the titania powder is prone to being agglomeration, hard separation and recycle. Filmy and supported titania have low photocatalytic activity. Focused on these problems, this paper introduces an improved sol-gel method without template, combined with centrifugal spinning and water vapor heat treatment process to prepare nanocystal self-supported continuous titania fibers. The novel photocatalyst is composed of active and base components. They not only have high photocatalytic activity, large surface area, but also easy separation and recyle. So it is a functional material that has wide application and developmental prospect.They were characterized by XRD, SEM, FTTR, UV-Vis DRS, XPS and N₂ adsorption-desorption. Furthermore, this paper investigates the degradation of several typical pollutants in water including X-3B, arsenic and bacteria. Also, the photocatalytic activity was associated with phase structure, granule morphology and characteristics of spectral response. The impacted factors of photocatalytic activity was discussed, too. This paper was divided into three parts as follows:In the first section, centrifugal spinning device was innovately manufactured applied in titania fiber preparation field. The device is inexpensive, simple to operate. The separared single fibers with different diameter were prepared by adjusting spinning rate and spinning pore size. Based on the technique, the three-dimensional titania fiber non woven cloth was obtained by changing spinning angle and floating rate. And photocatalytic water treatment device was explored combining optical fiber resulting in sufficient utilization for sun's rays. Three patents were warranted about them. Centrifugal spinning remedyed the disadvantage of electrospinning. It will play important role in inorganic fiber field.In the second section, the nanocystal self-supported continuous titania fibers were prepared using tetrabutyl titanate and tetraethyl orthosilicate as Ti and Si source by improved sol-gel method without any template. The fiber was above 1 metre long with a diametre of 10～50μm. The substrate were composed of titania nanocrystals and pores. The morphorlogy, surface area and pore structure were controlled by adjusting Si content. The product calcined under 700°C has the largest specific surface area and pore volume: 127.7 m²/g and 0.25 cm³/g, while the mole ratio of Si/Ti is 0.15. And it exhibites the highest photocatalytic activity for the degradation of X-3B. It mainly attributes to perfect anatase crystal structure, large specific surface area, pore volume and strong absorption to UV light. The kinetic data and adsorption isotherm for the adsorption As(V) accorded with pseudo-second rate equation and Freundlich equation. Adsorption was dominant with static gravitation. Adsorption isotherm for the adsorption As(III) was in agree with Freundlich equation, and surface compound played dominant effect. Photocatalysis made bacteria inactivation under ultraviolet light, and restrained bacteria increasing without ultraviolet light.In the third section, pure titania continuous fibers with abundant surface defect (Ti³⁺) were prepared using inexpensive titanium tetrachloride and tetraethyl orthosilicate as Ti and Si source through sol-gel process combining steam heat treatment. At low temperature, steam is catalyst to accelerate nucleation and crystallization. Meanwhile, abundant surface defect (Ti³⁺) were cteated through one-step crystallization avoiding high energy and time of conventional two-step crystallization. Compared to P25, the absorption edge of pure titania fibres appeared red shift. Its absorption intensity increases by 40 % in the wavelength larger than 400 nm. It exhibit high photocatalytic activity. The main reason may be that Ti³⁺ surface state was 0.3 eV below the conduction band of titania. So it can capture the photoelectron in the conduction band, increase photoinduced charge separation, decrease electron-hole recombination, and enhance the photo-catalytic efficiency. The new energy band-oxygen vacancy state (2.02～2.45 eV) was formed above valance band which is corresponding 506～614 nm. So the catalyst can absorb visible rays. Nevertheless, the doping of Si restrained the formation of Ti³⁺ and oxygen vacancy resulting in decreased absorption of visible rays and photocatalytic activity.