One photon, two reactions - new catalyst converts CO₂ and biowaste simultaneously

Researchers have developed a solar driven catalyst material that harnesses the energy of a single photon to reduce carbon dioxide and oxidise organic waste at the same time, and produce valuable chemicals in both reactions. 

Scientists at the University of Nottingham have created two catalyst materials which, when coupled together within the same reactor, can simultaneously convert carbon dioxide (CO₂) into a valuable chemical and biomass-derived feedstock into building blocks for sustainable plastics, driven solely by solar light. The research has been published in Communications Materials of the Nature Publishing Group.

A bias-free photoelectrochemical (PEC) reactor consists of two connected compartments, each containing the newly developed catalysts. When sunlight shines on one compartment, each photon drives the oxidation of a biowaste molecule. The electron released during this process is then transferred to the second compartment, where it reduces CO₂ to formate. 

This creates two useful products from the energy of a single photon: a valuable chemical derived from greenhouse gas, widely used in textiles, paints, and pharmaceuticals, and a precursor to next-generation bio-based plastics sourced from biowaste.

Dr Madasamy Thangamuthu, Research Fellow at the School of Chemistry, University of Nottingham, who designed the PEC reactor and catalysts, said: “At the heart of the process is a nanostructured photoanode made of carbon nitride and tungsten oxide semiconductors, enhanced with a cobalt oxide layer, which is coupled to a cathode in the second compartment. The process is initiated when a photon of solar light strikes the photoanode, generating an electron that travels to the cathode to reduce CO₂, while the remaining hole on the photoanode simultaneously oxidises the 5-Hydroxymethyl-2-furoic acid (HMFA) molecule.”

The PEC reactor with the new catalysts achieved remarkably high efficiencies of approximately 93% for CO₂-to-formate conversion and around 95% for biomass oxidation, showcasing efficient utilisation of photon energy. As the transformation is driven solely by solar energy, without the need for additional heat or electrical input, this approach presents exciting opportunities for sustainable chemical manufacturing.

Dr Vincenzo Taresco, Assistant Professor in the School of Chemistry, who specialises in polymeric materials synthesis, said: “Sustainable polymer production is one of the key challenges of our times. While advances in materials chemistry are progressing rapidly, new strategies are needed to drive these reactions efficiently. In this work, the use of solar light enables a clean process, ensuring that a sustainable energy source powers sustainable chemistry.” 

The catalysts developed by the Nottingham group differ from many existing catalyst materials that rely on expensive or scarce materials. Instead, these new catalysts are made from earth- abundant elements, making them more suitable for scalable applications. A life cycle assessment has further confirmed the environmental benefits of this process, emphasising its potential for low-carbon chemical manufacturing. In the future, this catalyst system could be scaled up for industrial use.

Dr Jesum Alves Fernandes, Associate Professor in the School of Chemistry, and expert in heterogeneous catalysis, said: “The method of catalyst fabrication is crucial for the future success of this technology. Our unique approach to the on-surface assembly of metal atoms into catalyst particles—specifically tailored in size, shape, and composition—will be essential for extending this work to other chemical processes and further enhancing CO₂ utilisation.”

The group has previously reported on the on-surface assembly of catalysts from individual atoms to create highly effective catalysts for hydrogen production and CO₂ conversion to methanol. 

The researchers believe that this approach can be further developed to integrate with industrial CO₂ sources and biorefineries, enabling distributed, sustainable chemical production.

Andrei Khlobystov, Professor of Nanomaterials at the School of Chemistry, said: “We are very excited about this breakthrough. Currently, humanity harvests only a tiny fraction of solar energy, most of which is converted into electricity. This discovery, however, opens new opportunities to capture sunlight directly to address two global challenges simultaneously. Using sustainable catalysts to drive both processes brings us closer to achieving UK and global net-zero targets.”

This work, funded by the EPSRC Programme Grant ‘Metal atoms on surfaces and interfaces (MASI) for sustainable future’ www.masi.ac.uk, represents a significant step towards reducing reliance on expensive metals for hydrogen production, thus contributing significantly to the circular and low-carbon economy.