A new material that can selectively capture CO₂ molecules and efficiently convert them into useful organic materials has been developed by researchers at Kyoto University, along with colleagues at the University of Tokyo and Jiangsu Normal University in China. They describe the material in an open access paper in the journal Nature Communications.

One possible way to counteract rising global CO₂ emissions is to capture and sequester carbon from the atmosphere, but current methods are highly energy intensive. The low reactivity of CO₂ makes it difficult to capture and convert it efficiently.

The new material is a porous coordination polymer (PCP, also known as MOF; metal-organic framework), a framework consisting of zinc metal ions. The researchers tested their material using X-ray structural analysis and found that it can selectively capture only CO₂ molecules with ten times more efficiency than other PCPs.

Direct structural information of confined CO₂ in a micropore is important for elucidating its specific binding or activation mechanism. However, weak gas-binding ability and/or poor sample crystallinity after guest exchange hindered the development of efficient materials for CO₂ incorporation, activation and conversion. Here, we present a dynamic porous coordination polymer (PCP) material with local flexibility, in which the propeller-like ligands rotate to permit CO₂ trapping.

… Owing to its high affinity towards CO₂ and the confinement effect, the PCP exhibits high catalytic activity, rapid transformation dynamics, even high size selectivity to different substrates. Together with an excellent stability with turnover numbers (TON) of up to 39,000 per Zn_1.5 cluster of catalyst after 10 cycles for CO₂ cycloaddition to form value-added cyclic carbonates, these results demonstrate that such distinctive structure is responsible for visual CO₂ capture and size-selective conversion.

—Wu et al.

The material has an organic component with a propeller-like molecularstructure, and as CO₂ molecules approach the structure, they rotate and rearrange to permit CO₂ trapping, resulting in slight changes to the molecular channels within the PCP. This allows it to act as molecular sieve that can recognize molecules by size and shape. The PCP is also recyclable; the efficiency of the catalyst did not decrease even after 10 reaction cycles.

One of the greenest approaches to carbon capture is to recycle the carbon dioxide into high-value chemicals, such as cyclic carbonates which can be used in petrochemicals and pharmaceuticals.

—Susumu Kitagawa, materials chemist at Kyoto University

After capturing the carbon, the converted material can be used to make polyurethane, a material with a wide variety of applications including clothing, domestic appliances and packaging.

This work highlights the potential of porous coordination polymers for trapping carbon dioxide and converting into useful materials, opening up an avenue for future research into carbon capture materials.

Resources

• Pengyan Wu, Yang Li, Jia-Jia Zheng, Nobuhiko Hosono, Ken-ichi Otake, Jian Wang, Yanhong Liu, Lingling Xia, Min Jiang, Shigeyoshi Sakaki & Susumu Kitagawa (2019) “Carbon dioxide capture and efficient fixation in a dynamic porous coordination polymer” Nature Communications volume 10, Article number: 4362 doi: 10.1038/s41467-019-12414-z