Newswise – Growing demand for carbon-based fuels to fuel the economy continues to increase the amount of carbon dioxide (CO2) in the air. While efforts are being made to reduce CO2 emissions, this does not mitigate the harmful effects of the gas already in the atmosphere. So researchers have come up with creative ways to use atmospheric CO2 by converting it into valuable substances such as formic acid (HCOOH) and methanol. Photoreduction of CO2 using photocatalysts using visible light as a catalyst is a popular method for such conversions.
In the latest breakthrough, revealed in the May 8, 2023, international edition of Angewandte Chemie, Professor Kazuhiko Maeda and his research team at Tokyo Institute of Technology have made significant progress. They have successfully developed a tin (Sn) metal-organic framework (MOF) that promotes the selective photoreduction of CO2. The recently introduced MOF was named KGF-10 and its chemical formula is [SnII2(H3ttc)2.MeOH]n (H3ttc: trithiocyanuric acid, MeOH: methanol). Using visible light, KGF-10 effectively converts CO2 to formic acid (HCOOH). Professor Maeda explained, “To date, many highly efficient photocatalysts for CO2 reduction based on rare and noble metals have been developed. However, integrating light-absorbing and catalytic functions into a single molecular unit composed of a large number of metals remains a challenge.” Thus, Sn proved to be an ideal candidate to overcome these two obstacles.”
MOFs, which combine the advantages of metals and organic materials, are being explored as a greener alternative to traditional photocatalysts based on rare earth metals. Sn, known for its dual role as a catalyst and light absorber in photocatalyst processes, could potentially be a viable option for MOF-based photocatalysts. Although MOFs composed of zirconium, iron, and lead have been extensively studied, understanding of Sn-based MOFs is still limited. Further studies and studies are needed to fully explore the possibilities and potential applications of Sn-based MOFs in the field of photocatalysis.
To synthesize tin-based MOF KGF-10, the researchers used H3ttc (trithiocyanuric acid), MeOH (methanol), and tin chloride as starting components. They chose 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole as an electron donor and hydrogen source. After synthesis, the obtained KGF-10 was subjected to various analytical methods. These tests showed that the material has a moderate CO2 adsorption capacity with a band gap of 2.5 eV and effective absorption in the visible wavelength range.
Armed with knowledge of the physical and chemical properties of the new material, the scientists used it to catalyze the reduction of carbon dioxide by visible light. Notably, the researchers found that KGF-10 achieves CO2 to formate (HCOO-) conversion with up to 99% selectivity without any auxiliary photosensitizer or catalyst. In addition, KGF-10 demonstrated an unprecedentedly high apparent quantum yield – a measure of the efficiency of using photons – reaching a value of 9.8% at 400 nm. Notably, structural analysis performed during the photocatalytic reaction showed that KGF-10 undergoes a structural modification to aid in the reduction process.
This groundbreaking research presents a high performance tin-based photocatalyst KGF-10 with no need for noble metals as a one-way catalyst for the reduction of CO2 to formate by visible light. The remarkable properties of KGF-10 demonstrated in this study could revolutionize its use as a photocatalyst in a variety of applications, including solar CO2 reduction. Prof. Maeda concludes: “Our results indicate that MOFs can serve as a platform for developing superior photocatalytic capabilities through the use of non-toxic, cost-effective, and abundant metals found on Earth, which are often molecular metal complexes. Unattainable.” This discovery opens up new possibilities. horizons in the field of photocatalysis and paves the way for the sustainable and efficient use of the Earth’s resources.
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