Two‐dimensional photonic metasurfaces for slow light‐controlled photocatalysis

Abstract

Photocatalysis using semiconductor materials like titania (TiO2) is a key method for environmental purification or solar fuel generation. Nanostructures that maximize incident light absorption are highly desired to enhance depollution rate or solar‐to‐fuel conversion efficiency in limited volumes of catalysts. Here, we report on structural and optical properties of metasurfaces based on a 20 nm thick anatase layer conformally deposited onto a wavelength‐scale two‐dimensional periodic photonic lattice. We investigate the NO degradation using such metasurfaces, and evaluate the impact of the patterning on photocatalytic activities between 340 and 400 nm. In the 380–385 nm range, the mean photochemical efficiency is increased by a factor up to 5.7 compared to flat references, with an overall three‐fold enhancement within the whole spectral range of interest. This approach can be applied to numerous types of systems by varying active materials, leading to substantial improvements in air/water depollution, water splitting or artificial photosynthesis processes.

Influence of the Micro-Nanostructuring of Titanium Dioxide Films on the Photocatalytic Degradation of Formic Acid under UV Illumination

“…However, this improvement may be due to different phenomena, in particular the increase in the contact surface area of Ti with the pollutant, or the improved light absorption. As suggested in another work, the improvement of the light absorption can increase the mean photochemical efficiency [ 41 ]. A 20 nm thick anatase layer conformally deposited onto a wavelength-scale two-dimensional periodic photonic lattice allowed the increase of the photochemical efficiency by a factor of up to 5.7 compared to the flat references [ 41 ].…”

“…As suggested in another work, the improvement of the light absorption can increase the mean photochemical efficiency [ 41 ]. A 20 nm thick anatase layer conformally deposited onto a wavelength-scale two-dimensional periodic photonic lattice allowed the increase of the photochemical efficiency by a factor of up to 5.7 compared to the flat references [ 41 ].…”

Optical Metasurfaces for Energy Conversion

“…Alternative to NPoMs, catalytic materials themselves can be nanostructured to form metasurfaces with fine-tailored absorption properties. Two prominent examples in this direction have shown that nanopatterned TiO 2 arrays can drive photochemical processes on their surface with enhanced reaction rates compared to thin films. , Despite the highly catalytic surface, the large band gap of TiO 2 creates difficulties in implementing the material for solar-driven chemical reactions. In the past decades, a wide variety of strategies have been used to narrow down the band gap to visible-IR spectral range, one of which include the hydrogenation of the TiO 2 to create a broadband absorbing “black” material .…”

“…The enhancement in the reaction rate was explained by the emergence of Mie resonances on the metasurface which served to improve the absorption of the material in the blue range, a feature that was lacking in the black control films. A similar TiO 2 metasurface structure was also investigated to demonstrate that environmentally relevant reactions, such as the degradation of NO in the atmosphere, can also be performed with such architectures . Further efforts now are expected to be concentrated in implementing such metasurfaces to a wider range of chemical reactions, particularly to artificial photosynthesis processes.…”

“…A similar TiO 2 metasurface structure was also investigated to demonstrate that environmentally relevant reactions, such as the degradation of NO in the atmosphere, can also be performed with such architectures. 905 Further efforts now are expected to be concentrated in implementing such metasurfaces to a wider range of chemical reactions, particularly to artificial photosynthesis processes. Taking a more hybrid approach, the combination of metasurfaces with tunnel junctions can help create nanoscale reactors that can simultaneously act as highly confined catalytic spots as well as multimodal optical sensors, aiding the in situ monitoring of hot-carrier mediated chemical reactions.…”