The modular and defined arrangement of nanoparticles over several length scales represents an attractive approach for creating an almost infinite variety of architectures from a limited number of building blocks [1]. Among the many possible geometries, three-dimensional and porous structures, such as those found in aerogels, are unique because, on the one hand, the size-specific properties of the nanobuilding blocks are fully preserved in the macroscopic material and, on the other hand, large surface areas are generated, which are crucial for efficient photocatalysis [2].
In this talk, a versatile strategy for synthesizing fully crystalline aerogels by gelation of the corresponding colloidal nanoparticle dispersions will be presented [3]. The composition, transparency and macroscopic geometry of the aerogels can be precisely tuned by carefully selecting the type of nanoparticles and their concentration in the colloidal dispersion as well as by controlling the gelation process [4]. These optimization strategies are demonstrated using the example of aerogels for gas-phase photocatalysis. In this case, it is important that the photoreactors are adapted to the shape of the aerogels [5]. In particular, gas flow through and illumination of the aerogels have a major influence on the efficiency of the photocatalytic gas phase reactions. Based on the example of photocatalytic hydrogen production from methanol, the influence of these parameters is shown and concepts are presented on how the systems can systematically be optimized.

References
[1] M. Niederberger, Multiscale Nanoparticle Assembly: From Particulate Precise Manufacturing to Colloidal Processing, Adv. Funct. Mater. 2017, 27, 1703647.
[2] M. Schreck, M. Niederberger, Photocatalytic Gas Phase Reactions, Chem. Mater. 2019, 31, 597.
[3] F. Matter, A.L. Luna, M. Niederberger, From colloidal dispersions to aerogels: How to master nanoparticle
Gelation, Nano Today 2020, 30, 100827.
[4] F. Matter, M. Niederberger, Optimization of Mass and Light Transport in Nanoparticle-Based Titania Aerogels, Chem. Mater. 2023, 35, 7995.
[5] F. Matter, M. Niederberger, The Importance of the Macroscopic Geometry in Gas-Phase Photocatalysis, Adv. Sci. 2022, 9, 2105363.