Water and air are vital for life – their pollution presents a big problem for humanity. The key to solving environmental and energy problems in the future is an efficient use of solar energy, which is a free, sustainable, and abundant source of energy. Photocatalysts are compounds that accelerate a wide variety of reactions using solar energy, including the production of added-value products and the decomposition of organic pollutants (to CO$_2$ and H$_2$O). The most researched photocatalyst is titanium dioxide (TiO$_2$), but its photocatalytic activity is limited by a high recombination rate of electron-hole pairs and a relatively wide band gap (3.2 eV for anatase), hindering the absorption of visible light. The photocatalytic activity can be improved by coupling TiO$_2$ with another semiconductor – for example cerium dioxide (CeO$_2$).
In the master's thesis, a procedure for sol-gel synthesis via the evaporation-induced self-assembly (EISA) method was established with controlled conditions (40 °C and 33 % relative humidity), followed by calcination. Mesoporous TiO$_2$, CeO$_2$ and TiO$_2$-CeO$_2$ composites were synthesized. Titanium(IV) butoxide was used as a TiO$_2$ precursor, and the mesoporous structure was achieved with the addition of the structure-directing agent Pluronic F127. TiO$_2$-CeO$_2$ composites were prepared with different amounts of cerium source using different approaches depending on the cerium source added: 1) cerium salts as CeO$_2$ precursors, 2) previously-synthesized CeO$_2$, and 3) a physical mixture of pre-synthesized TiO$_2$ and CeO$_2$. The photocatalytic activity of the materials was determined by monitoring the conversion of isopropanol to acetone with an FTIR spectroscopy in a gas-solid reactor system under UV and visible light illumination, and by the decomposition of the methylene blue dye in a liquid-solid system. The synthesized materials featured an average pore diameter of 5–7 nm and a high specific surface area. The photocatalytic activity was greatly influenced by the amount of the cerium source and especially by the synthesis approach. The physical mixtures were the most active, surpassing the activity of commercial TiO$_2$ P25 in the gas-solid system at all amounts of added cerium source.
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