Template Preparation Of Inorganic Hollow Fibers And Hollow Spheres

Inorganic hollow fibers have attracted considerable attention because of their potential applications such as in microreactors, supports, inorganic membrane separation and reactors, catalysis, gas sensors, and photovoltaics. Some techniques have been applied to the preparation of inorganic hollow fibers, such as dry/wet spinning and electrospinning an inorganic material system, supramolecular assembly, pyrolyzing the polymeric hollow fiber membranes, electrophoretic deposition, the template approach, etc. Among these techniques, the template approach is relatively simple and versatile in controlling the size and morphology of the inorgnic hollow fibers. The template preparation inorganic hollow fibers with diameter of several microns and length of about one millimeter were reported. In this paper, we present a new method to prepare TiO₂ hollow fibers by using poly(vinylidene fluoride) hollow fiber microfiltration membranes as the template. The idea of this technique is to fill the TiO₂ precursor into the pores of the polymeric membranes. After burning the polymeric component off, inorganic TiO₂ hollow fibers keeping almost the same structure and morphology as the template are formed. These hollow fibers were characterized by simultaneous differential scanning calorimetric analysis and thermogravimetric analysis, x-ray diffraction, and scanning electron microscopy. It was found that the outer diameters and the wall thickness of the TiO₂ hollow fibers could be adjusted by changing the polymeric hollow fibers with different sizes and the calcinations temperatures. Furthermore, The phase structure and the composition of each phase of the TiO₂ hollow fibers could be readily adjusted by changing the calcination temperature. On the other hand, by changing the configuration and shape of the polymeric template, inorganic TiO₂ hollow fibers with different configurations and shapes (such as spring and honeycomb) will also be prepared. By using the TiO₂ hollow fibers as supports, magnetic Ni-TiO₂ composite hollow fibers could be prepared by chemical plating. It was found that the Ni layers were tightly attached to TiO₂ layers. The thickness of the Ni layer could be adjusted by changing the chemical plating time. On the other hand, the tensile strength of the composite hollow fibers was stronger than TiO2 hollow fibers and increased with the increase of the chemical plating time. After 1.5 h of chemical plating, the tensile strength of composite hollow fibers reached 54.62 MPa, which is strong enough for various applications. Inorganic hollow spheres have attracted considerable attention because of their potential applications such as in controlling releasing capsules, artificial cells, shape selective catalysis and adsorption. Among them, TiO2 hollow spheres and metal hollow spheres are of great interests because of their outstanding catalytic properties. It is reported that the catalytic activity of TiO2 can be greatly enhanced by loading highly dispersed precious metals on TiO2 particles. If the precious metals are loaded on TiO2 hollow spheres, the composite materials can be more practically usable. Therefore, TiO2 hollow spheres supported Ag and Pd were prepared by a two-stage photocatalytic deposition method. TEM and XRD characterization indicated that the metals particles were highly dispersed. The sizes of Ag and Pd were about 4 and 15 nm respectively. On the other hand, Ni-TiO2 composite hollow spheres and Ni hollow spheres were simply synthesized by chemical plating method, using TiO2/PS spheres and polystyrene spheres as the templates respectively. Furthermore, by applying an ultrasonic treatment, Ni hollow spheres with a diameter of about 0.15 μm and a shell thickness of about 5 nm were prepared. These two types of hollow spheres were characterized by differential scanning calorimetric analysis and thermogravimetric analysis, x-ray diffraction, transmission electron microscopy, and transimission electron microscopy.