Microwave-coordinated KOH directionally modulated N/O co-doped porous biochar from Enteromorpha and its structure–effect relationships in efficient CO2 capture

To develop the CO2 adsorption capacity of Enteromorpha-based biochar, N/O co-doped porous biochar (NOBC) was directionally modulated by microwave-coordinated KOH, and the CO2 capture mechanism was explored by structure-effect relationship and density functional theory (DFT) calculations. NOBC with different porous structures and heteroatom contents were prepared by optimization of key parameters (microwave heating temperature, heating time, and KOH ratio) via Response Surface Methodology. The results showed that NOBC(700–20-3) had the maximum CO2 adsorption capacity of 6.09 mol/kg (273 K and 1 bar) and the CO2/N2 selectivity of 78.88 (298 K and 1 bar). After 5 cycles, the CO2 adsorption capacity of NOBC(700–20-3) was still up to 5.98 mol/kg (273 K and 1 bar), showing good cycling performance. The structure-effect relationship analysis showed that the CO2 capture performance of NOBC was proportional to the specific surface area, micropore ratios, graphitization degree, and heteroatoms contents, and inversely proportional to the mean pore diameter. DFT indicated that the synergistic effect between N and O elements developed the CO2 adsorption ability by boosting the affinity and electron transfer between NOBC and CO2. This work contributed to providing a theoretical basis and technical support for the targeted modulation of porous structures and improved surface properties of biochar for efficient CO2 adsorption.