Boosting the Mechanical Strength and Photocatalytic Activity of 3D-Printed Titania Aerogels by Atomic Layer Deposition and Heat Treatment

Titania aerogels are highly porous materials optimal for photocatalysis due to their high surface area. Further spatial structuring by 3D printing improves gas diffusion in the aerogel, leading to a higher photocatalytic activity. However, the aerogel's mechanical properties are reduced in comparison to non-3D printed aerogels. We hereby present an approach based on atomic layer deposition (ALD) of subnanometer-thin TiO₂ layers to compensate for that detrimental effect. The ALD-deposited TiO₂ consists of amorphous and anatase phase, with the anatase phase likely crystallizing on the aerogel's crystallites. Nanoindentation measurements confirm that the TiO₂ ALD-coatings improve the aerogel's mechanical properties. Additionally, it enhances the photocatalytic properties of the TiO₂ aerogel, which we attribute to the increased interface area and improved interconnection of the nanoparticle network. By further thermal postprocessing, it is possible to fully crystallize the ALD-deposited TiO₂, which shows a complementary effect on photocatalytic performance, improving hydrogen evolution rate by more than 1 order of magnitude from 6.35 to 125 μmol g^-1 h^-1. The combination of 3D structuring of aerogels with ALD coatings demonstrated in this work could be extended in the future to a wide range of materials where the interplay between mechanical and catalytic properties is vital.