Nanoengineered photocatalytic surfaces for wastewater treatment

Researchers from AMO GmbH and RWTH Aachen University have demonstrated an ingenious method to enhance the efficiency photocatalytic processes for wastewater treatment. The research has been reported in ACS Applied Nano Materials.

Water supply is becoming a major challenge in many areas of the world, calling for novel solutions for wastewater treatment and reuse. One of the challenges is getting rid of tenacious organic contaminants. These can be decomposed into harmless compounds by high-energy UV-light treatments, but the energy cost of these methods is currently too high for sustainable solutions.  A group of scientists lead by Dr. Ulrich Plachetka at AMO GmbH has now demonstrated a promising approach for using less energetic photons, paving the way to solar-driven wastewater treatment.

The key idea beyond this result is to combine structural and plasmonic effects to enhance the photocatalytic efficiency of titanium dioxide (TiO₂) – a material that is already employed as photocatalyst in wastewater treatments, but which normally requires the use of high-energy UV-light (UV-C). Plachetka and co-workers have now demonstrated that it is possible to achieve photocatalytic degradation of organic molecules under less energetic UV-light (UV-A) by depositing TiO₂ on a nano-engineered surface formed by a periodic array of glass cones covered by a thin film of gold. Most interestingly, the system proved able to decompose the organic dye methylene blue even under white light, indicating the potential of the approach for solar-driven wastewater treatment.

More specifically, the samples were fabricated by nanostructuring a glass surface to form a periodic grid of cones, with a diameter of 240 nm. A thin layer of metal (aluminum or gold) was then deposited on the cones, which were then finally covered by a thin film of TiO₂. The cones increase the effective area of the catalytic surface by nearly a factor of three and act as a diffraction grating, creating a light trapping effect. In addition, when covered by aluminum or gold, the cones act as plasmonic antennas, significantly enhancing the optical absorption of the TiO₂ film and its photocatalytic activity.

One of the most interesting aspects of the work is that the devices were fabricated using a scalable nanostructuring approach and conventional thin-film deposition methods, and could be therefore produced on large scale at low costs. Furthermore, the photocatalytic efficiency of the devices based on gold compares well with the one of TiO₂/metal nanoparticles (which today represent the state of the art) but completely circumvent the potential toxicological risks associated with nanoparticles.

Desislava Daskalova, the first author of the paper, explains: “The novelty of our work does not lie in any individual component of our photocatalytic surfaces, but in the successful combination of several approaches. From the fabrication perspective, nanostructuring of glass substrates is relatively easy and nanoimprint makes it scalable and cost-effective. From the scientific perspective, plasmonic photocatalysis paves the way to technologies based on solar-driven chemical reactions. We have demonstrated how this all comes together for advanced wastewater treatment, but the principle might be extended to also other photocatalytic processes.”

“This is a good example of how nanotechnology is instrumental for addressing global societal challenges,” says Prof. Max Lemme, Director of AMO GmbH. “At AMO, we have been developing nanostructuring techniques for years. Nanoimprint was a very active field of research in itself at the turn of the century. Now, it is one of the tools in our technology portfolio that we apply to find sustainable solutions for real-world problems, water management in this case.”

This scientific work is the result of the collaboration between AMO GmbH, the Chair of Electronic Devices (ELD) and the Institute for Environmental Engineering at RWTH Aachen University, and it contributes to the research pursued in the projects PEPcat and FreeHydroCells.

 

Bibliographic information:

“Combined Structural and Plasmonic Enhancement of Nanometer-Thin Film Photocatalysis for Solar-Driven Wastewater Treatment,” D. Daskalova, G. Aguila Flores, U. Plachetka, M. Möller, J. Wolters, T. Wintgens, and M. C. Lemme.

ACS Appl. Nano Mater. 2023
https://doi.org/10.1021/acsanm.3c02867 

This research was funded by the German Federal Ministry of Education and Research (BMBF) through the project PEPcat (02WCL1519A) and by the European Commission through the Horizon Europe Research and Innovation Programme, under grant agreement No. 101084261 (FreeHydroCells).