Study of photocatalytic activities of nanoscaled metal oxides on textiles

Abstract

A systematic study of the synthesis and application of nanoscaled metal oxides with photocatalytic activity was conducted. The synthesis was based on sol-gel nanotechnology at low temperatures and atmospheric pressure. The metal oxide sols were then applied to textile materials to form photocatalytic self-cleaning thin films by a dip-pad-dry-cure process. The main research work was focused on the synthesis, characterization, and application of pure anatase titanium dioxide (Ti02) and anatase titanium dioxide doped with other materials. The results showed that the anatase titania and its doped forms possess high photocatalytic activity, which was demonstrated by the complete decomposition of bacteria, colorants, red wine and coffee stains. Nanocrystalline anatase Ti02 sols were prepared under ambient pressure and at temperatures close to or approaching to room temperature using hydrolysis of titanium tetraisopropoxide in an acidic aqueous solution. A comprehensive study was carried out on the surface morphology, crystal phase and particle size of nanocrystalline Ti02 using field-emission scanning electron microscopy (FESEM), X-ray diffraction spectroscopy (XRD), and high resolution transmission electron microscopy (HRTEM). The effect of catalysts and different temperatures on the formation of anatase Ti02 and the self-cleaning performance of Ti02treated cotton fabrics under UV irradiation were evaluated. These Ti02 treated cotton fabrics possess significant photocatalytic self-cleaning properties, such as bactericidal activity, colorant decomposition and degradation of red wine and coffee stains. The UV absorption, the mechanical properties and durability of Ti02 treated cotton fabrics were investigated. Anatase Ti02 prepared by an aqueous sol-gel process at 60 °C was applied to polyester fabric since polyester is the most widely applied synthetic fibre in textile and clothing. Due to the poor adhesion between the Ti02 and polyester fibres, low temperature plasma (LTP) pretreatment of polyester fibres using oxygen gas was performed. The wettability of polyester towards the titania sol and the adhesion of titania layers to polyester fibres were improved as a result of the introduction of negative groups COO-,-O-O- onto polyester surface. The self-cleaning properties, such as bactericidal activities, colorant decomposition and degradation of red wine and coffee stains, of the anatase functionalized polyester fibers were studied. The surface morphological changes of polyester fibers before and after plasma treatment, and of plasma-treated fibers before and after applying anatase titania film were characterized by SEM. The adhesion between the anatase titania and polyester fibers was investigated. To improve the photocatalytic activity of Ti02 films, the anatase Ti02/Si02 nanocomposites were investigated. Anatase Ti02/Si02 nanocomposites were developed in an aqueous solution by a sol-gel process at a low temperature. The morphology of these nanocomposites was characterized by SEM, showing that Ti02 nanoparticles were deposited on the surface of Si02 spheres. The spherical TiO2/Si02 nanocomposites treated cotton fabrics demonstrated higher photocatalytic activity in comparison to pure Ti02 treated cotton fabrics in a typical photocatalytic test using a model compound of Neolan Blue 2G dye. The enhanced photocatalytic activities of the Ti02/Si02 treated cotton fabrics was considered attributable to the increased specific surface area and the enhanced surface acidity of nanocomposites. To eliminate the need for high temperature operations and the use of corrosive chemicals such as nitric acid and hydrochloric acid in synthesizing anatase TiO2, a new synthesis method for single-phase anatase Ti02 was developed using a sol-gel process in aqueous media followed by aging at room temperature. The self-cleaning activities of the as-prepared TiO2 thin films deposited on cotton fabrics were evaluated by the photodegradation of Neolan Blue 2G and the decomposition of red wine and coffee stains. The UV absorption, tensile strength and durability to laundering of the Ti02 treated cotton were also studied. This study further optimizes the synthesis conditions for anatase Ti02 which could contribute to the large scale fabrication of self-cleaning textiles. To extend the absorption of Ti02 into visible region of the spectrum and to reduce electron-hole recombination to further improve photocatalytic activity of Ti02 in UV-Visible region, Fe3+ doped Ti02 photocatalytic self-cleaning system was investigated. The synthesis was based on a sol-gel process in an aqueous solution at a temperature of 60 °C with the addition of Fe3+ dopant. The doping reduces the band gap energy and increases the wavelength response range extending to visible region. The Fe3+ dopant with various doping level was also studied. It was found that higher photocatalytic activity was achieved at optimum doping level compared to that of the pure Ti02 system under both UV irradiation and a visible light source without UV. The study revealed that anatase Ti02-based self-cleaning system is one of the most promising systems for the development of self-cleaning textiles that would have high potential in commercialization with the advantages of being environmentally friendly, low cost, energy and water saving due to the reduced laundry requirements of the treated items.