Synthesis and Post-Treatment Approaches for Porous and Crystalline TiO2 Aerogels

Kurzfassung

Photocatalytic hydrogen generation allows for hydrogen production with a low carbon footprint and low energy requirements for use as an alternative fuel source to fossil fuels. One requirement for efficient photocatalysis is an affordable and highly active catalyst with low toxicity. TiO2 aerogels therefor offer great potential photocatalysts for hydrogen generation. During this thesis, different titanium dioxide aerogels were produced by the sol-gel process on basis of titanium isopropoxide, ethanol, HCl and water. Two series of experiments were conducted: Series one foregoing any post-treatment approaches and focusing on altering the molar ratio of hydrochloric acid used during synthesis. Series two investigates effects of low temperature and low dwelling time thermal treatment in ambient, H2 and vacuum atmosphere. The primary goal of both series is to acquire a material with high surface area and pore volume while simultaneously achieving high degrees of crystallinity to allow high charge carrier mobility for photocatalytic processes. Resulting TiO2 aerogels are analyzed by methods of physisorption, PXRD, SEM, XPS, UV/VIS, TG-DSC and FT-IR. TiO2. Aerogels of series one show that increasing molar acid ratio results in an increase of pore width and broadening of pore size distribution. Crystallinity increases as well with increasing acid amount up to a molar ratio of 0.381. Temperature has a larger effect on crystallinity than dwelling time. Pore width increases with rising treatment temperatures while pore size distribution narrows for ambient and H2 thermal treatment. Vacuum thermal treatment showed a narrowing in pore size distribution and a decrease in pore width with rising temperatures indicating the presence of inaccessible pores in the investigated TiO2 aerogel system. An increase of Ti3+ defects was observed for vacuum thermal treatment at 300 °C while H2 and ambient thermal treatment show no increase in Ti3+ defects. The found crystalline TiO2 phase across all investigated samples is anatase.