Core-membrane microstructured amine-modified mesoporous biochar templated via ZnCl2/KCl for CO2 capture

Abstract

Mesoporous biochar (MC) derived from biomass is synthesized using a dual-salt template method involving ZnCl₂ and KCl, followed by impregnation with polyethyleneimine (PEI) of varying average molecular weights under vacuum conditions to construct a core-membrane structure for enhancing carbon capture performance. The resulting MC exhibits a highly intricate network of micropores and abundant mesopores, along with defects in graphitic structures, effectively facilitating robust PEI loading. Among the PEI-modified samples, PEI-600@MC demonstrates the highest CO₂ sorption capacity, achieving approximately 3.35 mmol/g at 0.1 MPa and 70 °C, with an amine efficiency of 0.32 mmol CO₂/mmol N. The introduction of amine functional groups in PEI significantly enhances the sorption capacity compared to bare MC. Additionally, PEI with lower average molecular weights exhibits a superior sorption performance at low pressures but shows a reduced thermal stability compared to higher molecular weight counterparts. The area of sorption hysteresis loops gradually decreases with increasing temperature and average molecular weight of PEI. The equilibrium sorption isotherms are accurately modeled by the Langmuir equation, revealing a maximum sorption capacity of approximately 3.53 mmol/g at 70 °C and saturation pressure. This work highlights the potential of dual-salts templated biomass-derived MC, modified with PEI, as an effective, widely available, and cost-efficient material for CO₂ capture.