Electrospun Preparation And Performance Of One-dimensional TiO₂ Based Photocatalytic Materials

Now, the energy crisis and environmental pollution are two big difficulties in human development. The abundant consumption of non-renewable fossil energy leads to serious environmental pollution. Changing the energy structure and developing renewable clean energy are two challenges that the scientists must face. As is known to all, solar energy is an ideal renewable clean energy, but solar energy is difficult to use because of its low energy density. Converting solar energy into available energy is an effective way to solve the energy crisis and environmental pollution. In 1972, Japanese scientists Fujishima and Honda reported photocatalytic water splitting for hydrogen generation on TiO2 electrodes. A few years later, Inoue reported photocatalytic reduction of greenhouse gas CO2 into hydrocarbon fuel in aqueous solution using semiconductor powder. Semiconductor photocatalytic technology is an important method of using solar energy. TiO2 photocatalysts have been widely studied due to cheapness, non-toxic, chemical inertness and light stability. TiO2 photocatalytic performance mainly restricted to the narrow scope of light absorption(< 387 nm) and high light-induced electron-hole recombination rate. Enhancing TiO2 photocatalytic performance is a hot spot in current research. This paper mainly studies the preparation of one dimensional electrospun TiO2 composites and their photocatalytic performance.First, we prepare the TiO2 nanotubes using the coaxial electrospinning technique. During the process of electrospinning, the outer needle was filled with precursor solution containing tetrabutyl titanate, polyvinylpyrrolidone and ethanol. The inner needle was filled with paraffin oil. During the process of calcination, paraffin oil will volatilize, the outer layer containing Ti precursor will convert into TiO2 crystal, so that we can obtain the TiO2 nanotubes. Then, TiO2-Ag-Cu2 O composite was obtained using surface deposition Ag and Cu2 O. The TiO2-Ag-Cu2 O composite photocatalyst shows better activity of photocatalytic hydrogen-production than TiO2, TiO2/Ag and TiO2/Cu2 O. The photocatalytic performance of the TiO2-Ag-Cu2 O sample exceeds that of the TiO2 nanotubes sample by more than 62 times. The corresponding apparent quantum efficiency of the TCA sample is 2.3% at 365 nm wavelength light irradiation. In the ternary system Ti O2-Ag-Cu2 O, the surface plasmon resonance effect of Ag has changed the charge transfer way between Cu2 O and TiO2. Through a series of characterization techniques, we put forward a kind of dual Z-scheme charge transfer mechanism and discuss this mechanism in detail.Second, preparing carbon nanofibers through electrospinning technology. The precursor solution of electrospinning was composed with polyacrylonitrile(PAN) and nitrogen dimethyl formamide(DFM). After two step sintering process, the carbon nanofibers were obtained. Then the carbon nanofibers were treated in strong acid solution for activated the surface of carbon fiber, and the TiO2 nanocrystals was grew on activated carbon nanofibers using hydrothermal method. This composite have carbon nanofiber@TiO2 core-shell structure. The photocatalytic reduction of CO2 tests indicate that the activity of carbon nanofiber@TiO2 core-shell composite shows 2.3-fold higher CH4 production rate than those of TiO2 nanocrystals obtained just through hydrothermal treatment. Through characterizations, we found that the improvement of performance could be attributed to the following.(1). The introduction of carbon fiber brings bigger specific surface areas which increases surface reactive sites;(2). The black carbon fiber can absorb more visible light, and the light energy can be converted into heat energy that can speed up the diffusion of reaction and product and then improve the efficiency of photocatalytic reaction;(3). The carbon fiber with good electrical conductivity can separate the light-induced electron-hole pairs in TiO2.