NH4Cl-assisted demineralization and intrinsic nitrogen reconstruction of crayfish shell waste to prepare N-rich porous carbons for flue gas CO2 capture

Solid adsorption is a promising approach for CO 2 capture owing to its low energy consumption. N doping can enhance the CO 2 adsorption capacity of porous carbon adsorbents. Conventional doping strategies rely on exogenous N additives (e.g., urea or melamine), and often suffer from low doping efficiency and potential environmental risks. Crayfish shells are attractive precursors for N-rich porous carbons owing to high N content, but their utilization is hindered by the high CaCO 3 content and the poor thermal stability of N species. Herein, we report an NH 4 Cl-assisted pyrolysis strategy that simultaneously enables in situ CaCO 3 removal, initial pore formation, and reconstruction of intrinsic N species into thermally stable N configurations. The prepared porous carbon contains 9.65 at.% N and achieves a CO 2 uptake of 4.44 mmol/g at 25 °C and 1 bar, with an isosteric heat of adsorption (Q st ) of 22.11–27.84 kJ/mol. Owing to its relatively low Q st , the adsorbent could be regenerated below 60 °C under an N 2 purge and retained 97.6% of its initial adsorption capacity after 15 cycles. The dynamic CO 2 /N 2 separation performance and the effect of H 2 O were evaluated under dry and wet flue gas conditions. Density functional theory (DFT) calculations and experimental results indicated that H 2 O played a dual role in CO 2 adsorption: competitive adsorption at N sites and pore blocking hindered CO 2 diffusion, whereas H 2 O-induced redistribution of the local electrostatic potential strengthened subsequent CO 2 adsorption. This work provides a feasible route for utilizing crayfish shell waste and developing intrinsically N-doped porous carbons for wet flue gas CO 2 capture.