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 CO 2 emissions. However, their complex fabrication procedures and high costs pose considerable challenges, frequently accompanied by ancillary CO 2 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 cm 3 ·g –1 following a simplified aging and ethanol washing procedure. Benefiting from its extensively developed porosity, PEI@AlOOH exhibited a notable CO 2 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 CO 2 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.