Direct air capture of CO₂ via aqueous-phase absorption and crystalline-phase release using concentrated solar power

Using negative emissions technologies for the net removal of greenhouse gases from the atmosphere could provide a pathway to limit global temperature rises. Direct air capture of carbon dioxide offers the prospect of permanently lowering the atmospheric CO₂ concentration, providing that economical and energy-efficient technologies can be developed and deployed on a large scale. Here, we report an approach to direct air capture, at the laboratory scale, using mostly off-the-shelf materials and equipment. First, CO₂ absorption is achieved with readily available and environmentally friendly aqueous amino acid solutions (glycine and sarcosine) using a household humidifier. The CO₂-loaded solutions are then reacted with a simple guanidine compound, which crystallizes as a very insoluble carbonate salt and regenerates the amino acid sorbent. Finally, effective CO₂ release and near-quantitative regeneration of the guanidine compound are achieved by relatively mild heating of the carbonate crystals using concentrated solar power.