The Role of Water in Carbon Dioxide Adsorption in Porphyrinic Metal‐Organic Frameworks

Abstract

Capturing and converting CO ₂ through artificial photosynthesis using photoactive, porous materials is a promising approach for addressing increasing CO ₂ concentrations. Porphyrinic Zr‐based metal‐organic frameworks (MOFs) are of particular interest as they incorporate a photosensitizer in the porous structure. Herein, the initial step of the artificial photosynthesis is studied: CO ₂ sorption and activation in the presence of water. A combined vibrational and visible spectroscopic approach was used to monitor the adsorption of CO ₂ into PCN‐222 and PCN‐223 MOFs, and the photophysical changes of the porphyrinic linker as a function of water concentration. A shift in CO ₂ sorption site and bending of the porphyrin macrocycle in response to humidity was observed, and CO ₂/H ₂O competition experiments revealed that the exchange of CO ₂ with H ₂O is pore‐size dependent. Therefore, humidity and pore‐size can be used to tune CO ₂ sorption, CO ₂ capacity, and light harvesting in porphyrinic MOFs, which are key factors for CO ₂ photoreduction.

Abstract

MOFs combined with photochemistry for CO ₂ photoreduction have great potential for addressing the challenge of reducing CO ₂ emissions. Herein, a combined visible‐infrared spectroscopic approach is reported to study the initial step of CO ₂ photoreduction: adsorption of CO ₂ in the presence of water into porphyrinic Zr‐MOFs. The findings will serve as guideline to tune adsorption site and photophysical properties of the photosensitizer.