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Solid amine adsorption is considered to be the most promising technology for post-combustion CO 2 capture, but it still has drawbacks due to the high cost of supports and the easy occurrence of CO 2 -induced chemical deactivation. Herein, we propose a novel eco-friendly method for realizing efficient and stable solid amine adsorbents. A calcium silicate hydrate (CSH) support with a pore volume of 3.0 cm3 g−1 is synthesized from coal fly ash (CFA) with the pore-expanded assistance of azeotropic distillation, and then the PEI@CSH adsorbents are prepared by impregnation. The adsorption capacity of the prepared 60%PEI@CSH-0.1 adsorbent reaches 198 mg g−1 and exhibits an excellent cyclic stability, with an attenuation of only 1.9% after 10 cycles under ideal regeneration conditions. Even under realistic regeneration conditions, the CO 2 uptake remains at 103 mg g−1 after 10 cycles, which shows obvious advantages over that of commercial SiO 2 supports. By using FT-IR, solid-state NMR and DFT calculations, we found that the CSH support promotes the conversion of primary amines to secondary amines in PEI molecules, and thus effectively inhibits the inactivation induced by the formation of urea compounds. Therefore, the PEI@CSH adsorbents provide a low-cost and high-efficiency approach for both in-situ CFA utilization and CO 2 mitigation inside coal-fired power plants. [Display omitted] • PEI@CSH adsorbents showed excellent adsorption capacity and cyclic stability. • The surface chemical property of CSH led to the anti-urea PEI@CSH adsorbents. • Solid-phase NMR and DFT calculation were applied for clarifying anti-urea mechanism. • PEI@CSH adsorbents realized both in-situ CFA utilization and CO 2 mitigation. [ABSTRACT FROM AUTHOR]