Development of high-performance adsorbent using KOH-impregnated rice husk-based activated carbon for indoor CO₂ adsorption

Relatively high indoor CO₂ concentration (greater than 1000 ppm) has a negative impact on human health. In this work, a cost-effective CO₂ adsorbent (DKOH-AC) was developed by impregnating KOH on rice husk-based KOH activated carbon (KOH-AC, 1439 m²/g). KOH can be successfully loaded on the surface of KOH-AC and significantly changed its surface properties. DKOH-AC still remained a considerable surface area (206 m²/g) and showed a similar S_micro/S_BET ratio. In-situ FTIR analysis confirmed that the major CO₂ adsorption mechanism of KOH-AC was based on physisorption while that on DKOH-AC involved both chemisorption and physisorption. DKOH-AC showed a higher heat of adsorption (34 ∼ 41 KJ/mol) and gas selectivity (16.6) than these of KOH-AC. KOH-AC quickly reached an adsorption equilibrium (about 50 min) as compared to that of DKOH-AC. In addition, DKOH-AC exhibited an excellent adsorption performance of 2.1 mmol/g for a low concentration of CO₂ (2000 ppm ∼ 500 ppm) under indoor conditions. Both the CO₂ adsorption isotherm on KOH-AC and DKOH-AC well followed the Langmuir and Freundlich models. The CO₂ adsorption kinetics on KOH-AC followed the pseudo-first order model whereas that on DKOH-AC obeyed the pseudo-second order model. The adsorption process was controlled by the intraparticle diffusion combined with the film diffusion model.