Mechanism of CO ₂ Adsorption on the Green Oxygen-Doped Hierarchical Biochar Activated by Dual Organic Salts

Excessive carbon dioxide emissions have led to global climate change, resulting in significant environmental impacts. Efficient CO₂ adsorbents are crucial for carbon dioxide capture. This study employs a green dual organic salt activation strategy to prepare a series of OPPCx (orange peel porous carbon) materials. Combining experimental results with DFT simulations, a reliable mechanism for CO₂ adsorption was proposed. Compared to the activation with sole C₆H₅K₃O₇, the introduction of C₁₂H₁₀Mg₃O₁₄ modulated the porous structure of the carbon material and enhanced the oxygen content and biochar yield. Micropore volume and surface oxygen functional groups are important factors influencing CO₂ adsorption. Oxygen functional groups exhibit strong electrostatic attraction to CO₂. The introduction of ketones (C═O), which have the highest content in the OPPCx samples, increased the adsorption energy by 109.9% compared to the original carbon substrate. The OPPC₃₁ sample exhibits the highest CO₂ adsorption capacity, reaching 4.31 mmol/g at 298 K and 1 bar. In addition, the OPPC₃₁ sample exhibits a moderate adsorption heat of 28.9 kJ/mmol, with an adsorption selectivity for CO₂ over N₂ of 17. The material also demonstrates good recyclability, as its adsorption capacity remains at 4.19 mmol/g (298 K, 1 bar) after five cycles, indicating that it is a promising CO₂ adsorbent material.