Investigation Of TiO₂-Based Nanofibers With Photocatalytic Properties By Electrospinning

VIII Towards the rapid development of the global industrialization process, the resultant energy crisis and environmental pollution problems have attracted more and more attention worldwide. Photocatalytic technology can not only degrade air and water pollutants, but also can convert low-density solar energy into high-density electric energy, which render itself practical significance to solve the energy crisis and environmental pollution. Among various semiconductor materials, titanium dioxide(Ti O2) is chemically stable, non-toxic, easily reduced, rich and cheap, so it becomes one of the most promising semiconductor that is widely used in photocatalysis filed. However, due to the relatively larger band gap(3.2e V), Ti O2 can only response to ultraviolet light, which accounts only about 4% of the total solar energy. Also, the light-induced electron-hole pair of Ti O2 is prone to recombine. Therefore, how to broaden the light response range of Ti O2 to improve the utilization of solar energy, and realize effective separation of photo-generated electron-hole, have become imminent issues on resolving Ti O2 as efficient photocatalyst. Compared with other methods, electrospinning technique generally results in better charge transport, lower carrier recombination, and higher porosity, etc., which makes it attract widespread attention. In addition, recent studies have proved that noble metal modified Ti O2 help broaden the light response range and increase the quantum yield. Therefore, this paper were explored from the following two aspects:(1) Pure Ti O2 nanofibers were one-step prepared via one-step electrospinning technology, combined with sol-gel method and high-temperature calcination process;(2) With the first part of this paper, Pt-doped Ti O2 composite nanofibers(Pt-Ti O2) were prepared successfully. Then, we investigated the photocatalysis degradation mechanism of Methylene Blue under ultraviolet and visible light irradiation, specifically as follows:(1)On the first part of my paper, polyvinyl acetate(PVAc) as the polymer matrix, titanium isopropoxide(Ti P) as titanium source, acetic acid as hydrolysis inhibitor of Ti P, ethanol and acetone as mixed solvent, pure Ti O2 nanofibers were one-step prepared successfully by adjusting the component content of spinning liquid, environmental parameters, electrostatic spinning parameters, combined with high-temperature calcination process. The produced pure Ti O2 nanofibers have a high length-diameter ratio, a large number of porous structures existing on the fiber surface, and the uniform diameter distribution. We further studied the impact of Ti O2 precursor on polymer nanofibers morphology, quantitatively analyzed the components content of PVAc/Ti O2 nanofibers, the effects of different calcination temperature on Ti O2 surface hydroxyl groups, crystal structure, photocatalytic activity, etc. We studied photocatalytic mechanism of Ti O2 nanofibers degrading methylene blue dye under UV irradiation. Results showed that Ti O2 nanofibers prepared at 500 ℃ has the highest photocatalytic activity.(2)The second portion is substantially in line with the first part of the paper, except the introduction of H2 Pt Cl6?6H2O in the spinning solution. H2 Pt Cl6?6H2O as a variable, a series of different Pt doped Ti O2 composite photocatalyst were prepared. We first prepared H2 Pt Cl6/Ti O2/PVAc composite fibers with spider-web structure, and preliminarily studied the formation mechanism of this unique structure. While Ti P is hydrolyzed to Ti O2 and crystallized, H2 Pt Cl6 thermally decomposed into Pt and then Pt is inserted into the Ti O2 lattice, forming Pt-Ti O2 heterojunction nanofiber structure. Pt element load level caused a significant impact on Ti O2 nanofibers morphology, crystalline structure, surface area, pore volume and pore size. Experimental results showed that the produced Pt-Ti O2 composite nanofibers has high photocatalytic activity under visible light irradiation; too little Pt doping is not conducive to the visible light absorption, and excess Pt doping leads to the formation of more electronic-hole recombination centers, so finally we found that the optimal amount of Pt doping is 1.20%.In this paper, electrospinning technology as the main method, we prepared pure Ti O2 and Pt-Ti O2 heterojunction composite nanofibers respectively to show that composite photocatalyst has a high photocatalytic activity under visible light irradiation by modifying Ti O2 nano-fibers. To some extent, we have made a useful exploration and set reference for electrospinning to preparing other nano-materials with high photocatalytic performance.