The activated carbons were conditioned to Carbon dioxide (CO₂) emissions from industrial activities continue to accelerate global warming, necessitating the development of efficient and sustainable post-combustion carbon capture technologies. Activated carbon produced from agricultural waste has emerged as a promising low-cost adsorbent for CO₂ capture; however, the influence of moisture on its adsorption performance remains insufficiently understood. This study investigated the effect of moisture content on the CO₂ adsorption capacity of activated carbon derived from palm kernel shell (PKS), coconut shell (CS), and groundnut shell (GS). The biomass precursors were carbonized at optimized temperatures of 750°C, 600°C, and 450°C, respectively, and chemically activated using potassium hydroxide (KOH). moisture contents of 0%, 5%, and 10% before CO₂ adsorption experiments were conducted at temperatures of 30°C, 40°C, and 50°C under pressures of 10, 15, and 20 psi using a locally fabricated flow-loop apparatus based on Sieverts' law. The adsorbents were characterized using Brunauer Emmett–Teller (BET) surface area analysis, Fourier Transform Infrared (FTIR) spectroscopy, and Scanning Electron Microscopy coupled with Energy Dispersive X-ray spectroscopy (SEM-EDX). The results showed that moisture significantly enhanced the CO₂ adsorption performance of all adsorbents. Palm kernel shell exhibited the highest adsorption capacity of 2.640 mmol g⁻¹ at 10% moisture, 50°C, and 20 psi, followed by coconut shell (2.298 mmol g⁻¹) and groundnut shell (1.300 mmol g⁻¹). Increasing the moisture content from 0% to 10% improved adsorption capacities by 240%, 189%, and 194% for PKS, CS, and GS, respectively. BET analysis further demonstrated that moisture conditioning increased the surface area and pore volume of PKS from 237.018 to 736.79 m² g⁻¹ and from1.177 to 2.853 cm³ g⁻¹, respectively, while FTIR analysis confirmed the formation of oxygen- containing functional groups and aromatic carbon structures that enhanced CO₂ adsorption. These findings demonstrate that moderate moisture levels (5-10%) substantially improve the adsorption performance of biomass-derived activated carbons by increasing pore accessibility and providing additional active adsorption sites through water-CO₂ interactions. Among the investigated adsorbents, palm kernel shell showed the greatest potential as an efficient and sustainable material for post combustion CO₂ capture in humid flue gas environments.

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