Transforming Coal Fly Ash into Climate Solutions: AlOOH-Supported Solid Amine Adsorbents for Cost-Effective and Ultranegative CO 2 Emissions

Solid amine adsorbents are emerging as a promising technology for achieving ultranegative CO₂ emissions. However, their complex fabrication procedures and high costs pose considerable challenges, frequently accompanied by ancillary CO₂ emissions and environmental repercussions. Herein, we developed a cost-efficient AlOOH-supported solid amine adsorbent (designated PEI@AlOOH), synthesized from coal fly ash. Aluminum was effectively recovered via a limestone-soda sintering approach, achieving an extraction efficiency as high as 98%. Subsequent synthesis of the AlOOH support yielded a high pore volume of 1.68 cm³·g^-1 following a simplified aging and ethanol washing procedure. Benefiting from its extensively developed porosity, PEI@AlOOH exhibited a notable CO₂ adsorption capacity of 178 mg·g^-1 in simulated flue gas environments. Concurrently, the high density of interlayer water and hydroxyl groups within AlOOH conferred exceptional urea resistance and cyclic stability for PEI@AlOOH, with only a 4.11% decline in performance over 30 operational cycles. A comprehensive life cycle assessment validated its exceptionally low carbon footprint and capture cost, registering merely 190.4 kg of CO₂ emissions per tonne captured and a capture cost of 252 $ per tonne, clearly outperforming existing alternatives. With continued innovation and process refinement, additional cost reductions are foreseeable, thereby reinforcing the industrial potential of PEI@AlOOH for large-scale deployment.