Insights into light and mass transport in nanoparticle-based aerogels: the advantages of monolithic 3D photocatalysts

The interest of nanoparticle-based aerogels—3-dimensional (3D) nanoparticle assemblies of macroscopic sizes—in photocatalysis is mainly their versatility for tailoring properties. However, little is known about the true viability of the aerogels as photocatalysts in part because of their 3D structure that is unusual for this application. Here, we investigate the mass and light transport effectiveness in the whole aerogel network and evaluate their photoactivity. We used anatase-based aerogels as model samples and designed a continuous-flow reactor to perform such analyses. It was found that the photons with suitable energy to initiate the reaction can propagate through the entire monolith because of their diffusive transport, making the 3D network fully active. The mass transport in the aerogels was also effective but is influenced by the reactor design. The aerogels showed promising activity, e.g., Pd-anatase aerogels with a volume of only 0.5 ± 0.04 cm3 generated 92 μmol h−1 of H2 with an apparent quantum efficiency of 13% at 375 nm.