Development of syntheses for nanostructured titania and silica
Abstract: Nanostructured titania is of great interest for a variety of energy and environmental applications, including conversion of solar energy, for energy storage systems and removal of organic pollutants in water and air. Titania is composed of earth abundant elements, it is environmentally friendly and chemically stable which makes it an attractive material to utilize. For many of the applications of titania, high surface area is beneficial, and it can be achieved by designing materials with structural features in the nanometer range, e.g. particles of a few nanometer in diameter and mesoporous materials with pore diameters in the range of 2-50 nm. In addition, the degree of crystallinity and the polymorph type have large effects on the physicochemical properties of the material. In this work, syntheses of titania nanoparticles and mesoporous titania and silica films were developed and the effect of varying relevant synthesis parameters on the structure on the atomic and nanometer scale was investigated. A low-temperature spray deposition method was developed to prepare ordered mesostructured titania and silica films via evaporation induced self-assembly (EISA) process, using a non-ionic block copolymer as a structure directing agent. The spray deposition method can be scaled up, the film thickness is tunable, surfaces of various shapes can be coated and heat sensitive substrates can be used. For the preparation of the mesoporous titania films, the polymer template was removed with UV radiation and the synthesis is carried out completely at temperatures below 50 °C. The effect of synthesis parameters, such as film thickness, synthesis time and aging time at high relative humidity on the structure at the atomic and nanometer scale were studied. Moreover, the prepared mesoporous titania was examined as an anode material in lithium ion batteries and the lithiation was studied in detail with electrochemical methods and structural characterization methods. In addition, titania nanoparticles were synthesized under acidic conditions at low temperature and the polymorph selectivity studied. Unexpectedly, selectivity towards rutile was observed with short synthesis time and related to high concentration of the titania precursor, whereas the selectivity towards brookite and anatase was related to lower concentrations of the precursor.
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