| In recent years, the increasingly serious environment pollution prompts the rapid development in the photocatalytic technology with non-toxicity and high-efficiency. TiO2nano-material is perhaps the most prospecting photo-catalyst. However, the nano meter TiO2materials including TiO2nanopowder, TiO2nanotube and TiO2nanofiber, is hard to separate and recovery from the water. Therefore, a lot of studies on macroscopic and fibrous TiO2catalyst have been recently carried out. In this paper, continuous titanium dioxide fiber (CTF) was successfully synthesized by sol-gel method, and the Ti sol fabrication mechanism and the effects of the processing parameters on the CTF were investigated. The pore formation mechanism on the TiO2surface was analyzed and the grain growth kinetics was brifly investigated. Then methylene blue and formaldehyde were used as the target pollutant to study the photocatalytic activity of the CTF. In addition, the CTF was modified by Si doping and (Si, N) co-doping. The main conclusions were drawn as following:Ti sol with spinnability was synthesized by sol-gel technique using the tetrabutyl orthotitanate as Ti source, and absolute alcohol as solvent. The effects of pH value, the molar ratio of distilled water to tetrabutyl orthotitanate (R), the molar ratio of PVP adhesive to tetrabutyl orthotitanate (P), oil bath temperature and time on the viscosity and rheological properties of the Ti sol were investigated, and the formation mechanism of spinning Ti sol was also analyzed. The optimal preparation conditions of Ti sol with spinnability were obtained:pH=5, R≤2, P=0.1%, the oil bath temperature120℃-135℃, and the oil bath time1-2hours. When R>2, the structure of the Ti sol changed from chain-like to three-dimensional network which presents poor spinnability.The CTF were successfully prepared by the Ti sol spinning and subsequent calcination treatment. The effects of calcination methods, calcination temperature and time on the microstructure and composition of the CTF were examined by SEM, TEM and XRD. The results showed that the samples obtained by air calcination and steam activation calcination methods had similar fiber diameter (20-30μm) and nano-particle size. The CTF calcined by the two calcination methods at500℃contained anatase and rutile phases. However, the specific surface area of the steam activation sample (32.27m2·g-1) was higher than that of the air calcination one (26.66m2·g-1). Through the kinetics analysis of the DSC curves, the activation energy of phase transformation from anatase phase to rutile phase was about96kJ·mol-1The grain growth kinetics of the CTF at500℃was researched. At500℃, the grain growth exponent and the rate constant is2,5.34×102nm2·h-1for anatase and4,1.91×107nm4·h-1for rutile TiO2phase. The carbonated organic on the surface of CTF could react with oxygen resulting from steam decomposition to form CO2. Then, the escape of CO2induced the pores formation on the surface of the CTF.Under25℃(reaction temperature) and25W (UV lamp power), the optimal photocatalytic reaction condition for methylene blue was as follows:the CTF concentration is0.6g·L-1, and the pH value is7. Under the same condition, the optimal CTF concentration and pH value for formaldehyde (10mg·L-1) photocatalytic reaction is0.5g·L-1and5, respectively.The Si-doped continuous TiO2fiber (Si-CTF) was prepared by in-situ method, then the (Si, N)-codoped continuous TiO2fiber ((Si, N)-CTF) was obtained by calcining the Si-CTF in nitrogen. Si-doping can improve the CTF precursor sol viscosity below40℃, and the sol has spinnability when the molar ratio S=5%(S=Si: TBOT). The diameter of nano-particles in Si-CTF (20nm) was smaller than that of CTF calcined at500℃, which indicate that the Si doping can inhibite the growth of TiO2nano-particle. In addition, XRD results showed that the Si doping or (Si, N) codoping could effectively depress the phase transformation from anatase to rutile. The MB degradation of Si-CTF and (Si, N)-CTF are69.2%and93.7%respectively. |
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