A low-energy approach to a reversible carbon dioxide capture strategy has been demonstrated by researchers from Renmin University of China. Solar radiation serves as the energy source and modified sawdust is used as the CO₂ absorbent in a system that enables use of the captured gas to generate methanol, ethanol and other products.

The CO₂ adsorbent, based on sawdust impregnated with an aqueous solution of low-molecular-weight amine-based polymer, does not require complicated synthesis and can trap CO₂ and be regenerated by solar heating. A reflector and sunlight absorption layer formed the sunlight harvesting system applied to heat the modified sawdust.

Schematic of the sunlight-controlled CO2 separation installation. Source: Shiming Zhang, Renmin University of China

In a proof-of-concept demonstration, a mixed gas consisting of CO₂ and nitrogen was treated by the sawdust-solar harvesting system. Half of the CO₂ in the mixed gas was rapidly extracted by the separation process within 6 minutes. The CO₂ concentration fell from 30.1% to 2.7% under a continuous illumination of solar light for 120 minutes, and 91% of CO₂ inside the test gas tank was successfully captured by sawdust. The target gas was also reversibly discharged from the separation system, thus renewing the sawdust as fresh CO₂ absorbent.

The research is published in Green Energy & Environment.