| Summary: | Biochar-based carbonaceous adsorbents are gaining interest due to their high availability, ease of modification, and low cost; however, they show limited adsorption of CO<sub>2</sub> in flue gas due to common textural properties. In this study, TEPA-modified biochar was used to prepare a solid amine adsorbent for the efficient capture of CO<sub>2</sub> in flue gas. First, the porous biochar was prepared with FeCl<sub>3</sub>, Mg(NO<sub>3</sub>)<sub>2</sub>, and H<sub>2</sub>O (g) as activators and walnut shells as carbon sources. Next, the biochar was modified with TEPA to obtain a solid amine adsorbent. Porous texture properties and sample surface functional groups were characterized, and we measured the adsorption CO<sub>2</sub> of the amine-modified biochar in a breakthrough adsorption device. Results showed that biochar has a large specific surface area (744.38 m<sup>2</sup> g<sup>−1</sup>), a total pore volume of 1.41 cm<sup>3</sup> g<sup>−1</sup>, and a high mesoporous volume ratio (82.7%). The high pore volume provided a more efficient support space for loading tetraethylenepentamine (TEPA). The adsorbent had an excellent CO<sub>2</sub> adsorption capacity, corresponding to 2.82 mmol g<sup>−1</sup>, which increased to 3.31 mmol g<sup>−1</sup> and kept water resistance at 10% H<sub>2</sub>O (g) simulated flue gas (SFG). The FTIR analysis showed that H<sub>2</sub>O (g) inhibited urea production after cyclic adsorption. Therefore, solid amine adsorbent created by amine-modified biochar has potential advantages in its application for capturing CO<sub>2</sub> in SFG.
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