The conversion of light into heat is an essential process for a wide range of technologies such as solar thermal heating, photoacoustics, (photo)catalysis, and desalination. 3D nanomaterial-based aerogels and foams have shown great promise as photothermal transducer materials. However, light-to-heat conversion is physically limited by surface near-absorption, resulting in strong heat localization only at the illuminated surface region, while most of the transducer material volume remains unused for light-matter interaction.
We present an innovative fabrication concept for 3D hierarchical and highly porous (>99.9%) hybrid aeromaterial transducers that enable ultra-fast and volumetric photothermal response with a factor of ~2.5 improvement over the state-of-the-art. The hybrid aeromaterials are based on hierarchical framework structures composed of interconnected hollow silicon dioxide (SiO2) microtubes, providing a platform with strong light scattering properties [1], functionalized with extremely small amounts (in the order of a few µg cm-3) of reduced graphene oxide (rGO) nanosheets [2], acting as photothermal agents. Tailoring the density of rGO within the hierarchical framework structure enables us to control both light scattering and light absorption, and thus a volumetric photothermal response. Utilizing the synergistic effect, the enhanced photothermal interaction volume in combination with the high surface area and low volumetric heat capacity of the porous transducer material enables ultra-rapid activation of macroscopic gas volumes [3], opening up new functionalities and application scenarios based on light-to-heat conversion, such as untethered light-driven and -controlled microfluidic pumps and soft pneumatic actuators. Extending the concept, it is conceivable to use the photothermal transducer materials for photocatalysis applications by additional functionalization with catalytic nanomaterials.