Newswise — The ceaseless need for carbonaceous fuels to fuel the economy continues to augment the quantity of carbon dioxide (CO2) in the air. Although endeavors are underway to decrease CO2 emissions, this alone cannot mitigate the detrimental consequences of the gas already existing in the atmosphere. Hence, researchers have devised ingenious means to utilize the present atmospheric CO2 by converting it into valuable substances like formic acid (HCOOH) and methanol. Employing visible light as a catalyst, the photoreduction of CO2 via photocatalysts stands as a popular technique for accomplishing such transformations.
In a recent breakthrough disclosed in Angewandte Chemie, International Edition on May 8, 2023, Prof. Kazuhiko Maeda from the Tokyo Institute of Technology and his team of researchers achieved a significant advancement. They successfully developed a metal-organic framework (MOF) based on tin (Sn), which facilitates the selective photoreduction of CO2. The newly introduced MOF, designated KGF-10, possesses the chemical formula [SnII2(H3ttc)2.MeOH]n (H3ttc: trithiocyanuric acid and MeOH: methanol). Through the utilization of visible light, KGF-10 effectively converted CO2 into formic acid (HCOOH). Prof. Maeda explains, "Many highly efficient photocatalysts for CO2 reduction reliant on rare and valuable metals have been developed so far. However, the integration of light absorption and catalytic functions within a single molecular unit composed of abundant metals has long been a persistent challenge. Therefore, Sn proved to be an ideal candidate, capable of overcoming both of these obstacles."
MOFs, which combine the advantages of both metals and organic materials, are being investigated as a greener substitute for traditional photocatalysts that rely on rare-earth metals. Sn, recognized for its dual role as a catalyst and light absorber in photocatalytic processes, holds potential as a viable option for MOF-based photocatalysts. While MOFs composed of zirconium, iron, and lead have undergone extensive exploration, the understanding of Sn-based MOFs remains limited. Further research and investigation are necessary to fully explore the capabilities and potential applications of Sn-based MOFs in the field of photocatalysis.
To synthesize the Sn-based MOF KGF-10, the researchers utilized H3ttc (trithiocyanuric acid), MeOH (methanol), and tin chloride as the initial components. As an electron donor and hydrogen source, they selected 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole. Following the synthesis, the prepared KGF-10 underwent various analysis techniques. These examinations unveiled that the material exhibited a moderate ability to adsorb CO2, possessed a bandgap of 2.5 eV, and effectively absorbed visible light wavelengths.
Equipped with knowledge regarding the physical and chemical characteristics of the novel material, scientists harnessed it for catalyzing the reduction of CO2 in the presence of visible light. Remarkably, the researchers discovered that KGF-10 achieved the conversion of CO2 into formate (HCOO-) with an impressive selectivity of 99%, without requiring any supplementary photosensitizers or catalysts. Additionally, KGF-10 exhibited an unprecedentedly high apparent quantum yield—a measure of the efficiency of photon utilization—reaching a value of 9.8% at 400 nm. Notably, structural analysis conducted during the photocatalytic reactions revealed that KGF-10 underwent structural modifications while facilitating the reduction process.
This groundbreaking study introduced a tin-based photocatalyst, KGF-10, which exhibits high performance, eliminates the need for precious metals, and functions as a single-component catalyst for the visible-light-driven reduction of CO2 to formate. The exceptional properties displayed by KGF-10 in this research have the potential to revolutionize its utilization as a photocatalyst in various applications, including solar energy-driven CO2 reduction. Prof. Maeda concludes, "The outcomes of our investigation serve as evidence that MOFs can serve as a platform for developing remarkable photocatalytic capabilities, typically unachievable with molecular metal complexes, by employing non-toxic, cost-effective, and abundant metals found on Earth." This discovery opens up new horizons in the field of photocatalysis and paves the way for sustainable and efficient utilization of Earth's resources.
RSS