Upcycling Wood Waste into Solar-Driven Regenerative Sorbent for Direct Air Capture

Direct air capture (DAC) is a promising negative-emission technology for mitigating climate change caused by excessive atmospheric CO₂ emissions. Amine-functionalized solid adsorbents exhibit a strong affinity for CO₂ in ambient air, making them attractive for DAC systems. However, their regeneration for reuse typically requires a high energy use during thermal swing processes. Herein, we upcycle wood waste into a DAC adsorbent that can release CO₂ via solar light irradiation for an energy-saving DAC process. Importantly, the as-synthesized adsorbent in situ preserves lignin, enabling photothermal heating without addition of photothermal fillers into a complex composite. The as-synthesized adsorbent exhibits a CO₂ uptake of 1.84 mmol/g at 25 °C, rapidly reaching 50% of its capacity within 7 min, and releasing 50% of CO₂ in 22 min at 67 °C under solar illumination. Moreover, this study found the presence of water vapor enhances the CO₂ adsorption capacity of the adsorbent, making it particularly advantageous for CO₂ capture under humid air conditions. This work demonstrates a straightforward approach for developing solar-driven regenerative CO₂ adsorbents based to a large fraction on waste lignocellulosic biomass, offering a promising pathway to sustainable and energy-efficient DAC.