Semiconducting Titania Aerogels of tunable Crystallinity and Polymorphs

Abstract

Within this work we will present novel sol-gel based synthesis routes for (semi-)crystalline Titania aerogels. Based on the synthesis procedure material parameters such as surface area, the polymorph present in the sample and the degree of crystallinity can be controlled. Providing an alternative synthesis route for highly porous, highly crystalline Titania samples with specific surface areas of up to 600 m² g-1 can be obtained without calcination steps and thus obtain the open porous 3D structure. The aerogel properties can be selectively controlled by the respective synthesis parameter. Especially, the direct influence of acid concentration was investigated on. Due to the dependence on the steric hindrance of the alkoxy ligands, the applied chloride ions coordinate in different ways to the used Titania precursor which changes the hydrolysis and condensation reaction kinetics. Also, the usage of different solvents led to a ligand exchange of the Titania precursor which lead to different intermediate complexes with coordinated chloride ions that act as templates for the formation of mixtures of anatase and brookite polymorph with tunable ratios. In-situ analysis methods such as Raman spectroscopy, revealed the polymorph growth during three to seven days of aging in the wet gel state. Here, we would like to focus on diffraction analysis of the as prepared aerogels depending on the synthesis parameter as well as in-situ and ex-situ Raman spectroscopy for direct polymorph identification and the polymorph stability and evolution on thermal treatment.