Light-swing CO2 capture: photoirradiation-based chemical CO2 release based on photoisomerization of azobenzene-amine/guanidine derivatives†

The world is committed to reducing CO₂ emissions, and research on CO₂ capture and effective utilization is being actively studied. Among the methods in development, direct air capture (DAC) is classified as a negative emission technology and has attracted significant study. The current problem with CO₂ capture technologies for decarbonization is their cost due to the high separation energy required to release CO₂. We have developed a new light-swing method that can potentially utilize a natural source of energy, i.e., sunlight, as an alternative to temperature- and pressure-swing methods. Herein, we report photoirradiation-based CO₂ capture based on photoisomerization of azobenzene-amine and guanidine derivatives. The visible light-swing CO₂ absorption and release system using azobenzene-guanidine has shown potential in DAC systems owing to its reusability. A plausible mechanism for CO₂ release under light irradiation involves photoisomerization from trans- to cis-azobenzene in which steric repulsion with other molecules is the driving force, and CO₂ is released due to the functional disruption of intermolecular interactions. This concept demonstrates the potential of using various photokinetic molecules as a driving force for light-swing CO₂ capture.