<p>This study presents an efficient method for CO₂ capture and separation using low-cost corncob-based activated carbon/metal nanoparticles (MNPs/AC) composites. Initially, the optimization of AC synthesis was conducted by varying activating agent/precursor ratios and activation temperature. Subsequently, the highly porous AC was modified using a polyol method with a single and binary mixture of Cu²⁺ and Zn²⁺ metals. The raw AC, Cu/AC, Zn/AC, and Cu–Zn/AC composites were extensively characterized through BET, FESEM-EDX, FT-IR, TGA, and Boehm’s titration analyses. Gas adsorption results revealed that the bimetallic composite sample, Cu–Zn/AC, demonstrated the highest CO₂ capture capacity of 5.41 mmol/g compared to the parent AC (3.25 mmol/g) as well as the single metal-doped ACs, Cu/AC (4.19 mmol/g) and Zn/AC (4.38 mmol/g) at 1 bar and 25 °C due to stronger synergistic effects. In addition, the selectivity of CO₂/N₂ and CO₂/CH₄ was also studied for samples using the Ideal Adsorption Solution Theory (IAST) at 25&#xa0;°C&#xa0;and 1 bar. Among all samples, Cu–Zn/AC showed excellent selectivity towards CO₂/N₂ and CO₂/CH₄ with values of 65 and 16, respectively. The higher selectivity for metal-doped samples compared to the pristine AC is due to a stronger interaction between the introduced MNPs and CO₂ molecules, as indicated by the higher isosteric heat of CO₂ adsorption. These results suggest that the bimetallic (Cu–Zn) doped AC is an effective and low-cost adsorbent for natural gas upgrading and flue gas CO₂ capture.</p> Graphical Abstract <p></p>