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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]

Amine-functionalized adsorbents have become a hot topic in research on CO 2 separation from biogas. However, developing superior adsorbents with high adsorption capacity and stable cyclic stability under a CO 2 regeneration atmosphere remains difficult. In this study, azeotropic distillation, a green, recyclable method, was used to expand the pores of the nano-Al 2 O 3 support. The pore volume of pore-expanded nano-Al 2 O 3 reached 1.62 cm3 g−1, and the derived amine-functionalized nano-Al 2 O 3 adsorbent ('60%PEI@AD-Al 2 O 3 ') possessed a superior CO 2 uptake of 199.4 mg·g−1 adsorbent with rapid adsorption kinetics. '60%PEI@AD-Al 2 O 3 ' showed favourable cyclic stability under CO 2 regeneration atmosphere with a final CO 2 uptake of 133.8 mg·g−1 adsorbent after 50 cycles, which possessed a competitive CO 2 uptake compared with the reported amine-functionalized adsorbents with anti-urea stability. This superior performance is attributed to the large pore volume of the pore-expanded nano-Al 2 O 3 support and the anti-urea stability for '60%PEI@AD-Al 2 O 3 ', which does not require active amine modification and avoids diluting the active amine content. Furthermore, the effect of water vapour in biogas on adsorption performance was studied. Water vapour could significantly promote CO 2 adsorption at low temperatures (<90 °C), and it was accompanied by strong water vapour adsorption, which would potentially increase the regeneration energy consumption. Additionally, water vapour could effectively inhibit the formation of urea compounds, further improving the cyclic stability. Because of the facile, scalable preparation method, the synthesised amine-functionalized nano-Al 2 O 3 adsorbent has broad application prospects for CO 2 separation. [Display omitted] • Nano-Al 2 O 3 was pore-expanded via n-butanol solvent to a pore volume of 1.62 cm3 g−1. • Polyethylenimine was impregnated on nano-Al 2 O 3 for CO 2 separation from biogas. • '60%PEI@AD-Al 2 O 3 ' adsorbent shows superior CO 2 uptake of 199.4 mg·g−1 adsorbent. • '60%PEI@AD-Al 2 O 3 ' adsorbent possesses favourable cyclic and anti-urea stability. • Water vapour can inhibit the urea formation and improve the cyclic stability. [ABSTRACT FROM AUTHOR]