Denaturing Agents in the Synthesis of Titanium Dioxide Aerogels & Relaxometry as a Fast Analysis Method for Prous Media

Kurzfassung

Titanium dioxide (TiO2) is a promising material for various photocatalytic applications including hydrogen generation by water splitting and ammonia synthesis by nitrogen reduction. For realizing such applications the catalyst’s efficiency is crucial. Because of their large surface area, good designability, and the high number of reactive sites (semi-)crystalline TiO2-aerogels are very promising advanced materials to bring titanium dioxide to the next level as a photocatalyst. To enable commercial large-scale synthesis of such aerogels it is important to use inexpensive reactants and solvents but past investigations showed that the properties of TiO2-aerogels change when cheaper denatured ethanol is used in the synthesis instead of more expensive non-denatured ethanol. Thus here the influence of the commonly used denaturing agents denatonium benzoate (Bitrex) and methyl ethyl ketone (MEK) on different structural and electronic properties of TiO2-aerogels are investigated in detail. It is found that MEK does not influence the properties of TiO2-aerogels at all but that Bitrex has a significant impact on the formed 3-dimensional network of the gels and their photocatalytic properties. The benzoate anions from the Bitrex coordinate to the titanium atoms of the used precursor and are incorporated into the network structure in the gelation process. They thereby cause distortions of the Ti-O lattice and promote the formation of larger pores. An additional challenge in the synthesis of aerogels is that the gels must be dried before most standard analysis methods can be conducted. For the application as catalysts, the surface area and pore structure of gels are particularly interesting properties, which are usually investigated via gas physisorption measurements. In this work, it was tried to implement NMR relaxometry as an alternative to this state-of-the-art method, which is multitudes faster than physisorption measurements and can also be conducted with nondried gels. This was not successful yet but laid the foundation for further experiments and fostered new ideas for manipulating the properties of alco- and hydrogels.