Preperation Of TiO₂–based Composite Nanofibers And Study Of Their Photocatalytic Performances

In the last two decades, nanoscience appears an amazing rise by advances in the synthesis and interdisciplinary research of the properties of nanostructures and nanomaterials, such as large specific surface area, small size effect, surface and interface effect and quantum size effect, inwhich at least one of the dimensionalities fall in the 1–100 nm. The size of nanomaterials can affect their properties, such as electronic, optical, magnetic and mechanical properties, owing to quantum confinement of electrons or Wannier excitons in three–dimensional（3D）, two–dimensional（2D）, one–dimensional（1D）, and zero–dimensional（0D） nanostructures. The possible technological applications have promoted the rapid development of the field. The excellent control over the size, composition, crystal structure, surface chemistry and solid–state properties of 0D and 1D nanostructures of inorganic semiconductors and metals brings about the advanced properties of the nanomaterials. 1D nanostructures contain nanofibers, nanowires, nanotubes, nanobelt, et al. There are many methods to prepare the 1D nanofibers, such as hydrothermal synthesis method, chemical vapor deposition method, template method, electrospinning method, and so on.Electrospinning, as a versatile method to produce functional nm to mm fibers, is widely used in the processing of fibers for various applications in the fields of energy, healthcare and environmental engineering. Electrospinning method can not only synthesize organic nanofibers, but also prepare inorganic nanofibers. After the subsequent calcined process, only inorganic compound leave, the polymeric substance in composite nanofibers are removed, which makes the defects stay on the fibers. As active sites, the defects on inorganic nanofibers can make the catalytic, sensing and medical performance much higher. Moreover, modified nanofibers with some semiconductors or metals can improve the function of the fibers.In this paper, tetrabutyl titanate/polyvinylpyrrolidone（TBT/PVP） composite nanofibers were prepared by electrospinning method. Then TiO₂ nanofibers were obtained after calcining TBT/PVP. TiO₂ nanofibers were modified with metal（M） and metal sulfide（MS） with different chemical processes. Metal oxide（MO） doping TiO₂ composite nanofibers were synthesized by electrospinning and calcination method. The main contents are as the following:1. TiO₂ nanofibers were prepared combining electrospinning and calcination method. Ag+ adsorbed on the surface of TiO₂ nanofibers was reduced to Ag0 by in situ reduction method under UV light irradiation, and then Ag–TiO₂ composite nanofibers were obtained. The photocatalytic degradation performance was analyzed by degrading methyl orange solution. And the photocatalytic hydrogen production performance was evaluated with methanol solution as sacrificial agent. Experimental results show that the photocatalytic performances of TiO₂ nanofibers were significantly improved after loading Ag particles. With the increasing of Ag content, the value of photocatalytic performances is improving. When Ag content reaches 5%, the photocatalytic performance is optimal.Utilizing the reducing capacity of Ethylene glycol, we prepared Ni–TiO₂ composite nanofibers by hydrothermal method under high temperature and high pressure. The structure and morphology of Ni–TiO₂ nanofibers were characterized through XRD, XPS, SEM and TEM. The synthesis mechanism was also studied.2. Three kinds of MS–TiO₂ composite nanofibers were synthesized by electrospinning and hydrothermal methods. First, we prepared popcorn–like Cd S nanoparticles using hydrothermal method. Its structure and morphology were studied through SEM, TEM, XRD and EDX. The synthesis mechanism was also conjectured. Using methyl orange as degradation substrate, the photocatalytic degradation performance of Cd S nanoparticles was evaluated.On the basis of the synthesis of Cd S nanoparticles, we prepared bud–like Cd S–TiO₂ composite nanofibers. The synthesis mechanism of Cd S–TiO₂ nanofibers was conjectured, which was based on the synthesis mechanism of Cd S nanoparticles. Through the study of Cd S composite nanofibers’ optical properties, it found that the light response range of the composite nanofibers was broadened to the visible light region, and the photocatalytic degradation capability of the composite nanofibers was much higher than that of pure TiO₂ nanofibers.Using the same preparation method of Cd S–TiO₂ composite nanofibers, Zn S–TiO₂ composite nanofibers were also synthesized. The structure and morphology of the nanofibers were analyzed by XRD, XPS, EDX and SEM. Compared with TiO₂ nanofibers, the optical property of Zn S–TiO₂ was obviously enhanced.At last, Cu S–TiO₂ composite nanofibers were prepared using the same method. The structure and morphology of the nanofibers were analyzed and its optical property was also studied.3. MO（Zn O, Ni O, Cu O and Co₃O₄） doping TiO₂ composite nanofibers（MO/TiO₂） were prepared by electrospinning and calcination method. The structure of MO/TiO₂ was studied using XRD, XPS and EDX. The morphology of MO/TiO₂ nanofibers was investigated by SEM and TEM. Thermo–gravimetric processes were measured by TGA. Ultraviolet visible diffuse reflectance spectrum of Zn O/TiO₂ and Ni O/TiO₂ composite nanofibers was evaluated also. Experimental results show that doping MO can extend the absorption region of optical spectrum, which may improve the optical property of nanofibers.