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[Display omitted] • KOH was impregnated on rice husk KOH-activated carbon, named as DKOH-AC. • DKOH-AC involved both chemi- and physi-sorption when KOH-AC allowed physi-sorption. • CO 2 adsorption on DKOH-AC followed Freundlich and pseudo second order models. • DKOH-AC adsorbed 2.1 mmol/g in an indoor condition. Relatively high indoor CO 2 concentration (greater than 1000 ppm) has a negative impact on human health. In this work, a cost-effective CO 2 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 CO 2 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 CO 2 (2000 ppm ∼ 500 ppm) under indoor conditions. Both the CO 2 adsorption isotherm on KOH-AC and DKOH-AC well followed the Langmuir and Freundlich models. The CO 2 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. [ABSTRACT FROM AUTHOR]

[Display omitted] • Leaching of the valuable metals and utilizing carbon residue from spent lithium-ion batteries. • K 2 CO 3 impregnated carbon utilized as an adsorbent for indoor CO 2 capture. • An investigation of the reaction mechanism for CO 2 adsorption on supported K 2 CO 3 under humid condition. • At low CO 2 concentrations, the CO 2 adsorption capacity for K 2 CO 3 /carbon ranged from 5.1 to 7.3 wt% Recycling and reusing the carbon-residues (i.e., graphite), as well as recovering valuable metals by leaching from spent lithium-ion batteries, is environmentally and economically significant. In particular, since a large amount of spent lithium-ion batteries (LIBs) will be generated along with the rapid growth of electric vehicles (EVs), research on recycling carbon-residues from LIB anodes is urgently needed. Herein, the battery powder (BP) was obtained from spent lithium-ion batteries (LIBs) through physical-pyrolysis and sieving. Chemical composition analysis confirmed that the battery used in this work was composed of NCM cathode with high-nickel content and graphite anode material. The average particle size of the obtained BP was 87 μm. In order to obtain the residue having high concentration of carbon, the metal extraction was applied using an HCl solution. As a result, metals (Li, Ni, Co, Mn, Al, Cu, and Fe) in the final remnant were found to be less than 2%, and carbon was found to have a purity of 97% or more. The obtained BP was tested as both the adsorbent and support for indoor CO 2 capture. Various activation treatments were examined to enhance the textural properties of BP. BP-K (K 2 CO 2 impregnated BP) adsorbents were prepared, and their CO 2 adsorption performances were evaluated with CO 2 adsorption isotherms, thermogravimetric analysis (TGA), and 0.1 m 3 chamber (CO 2 IR analyzer) at low CO 2 level (1000–2000 ppm). Through XRD and FT-IR analyses, the adsorption mechanism between K 2 CO 3 and CO 2 under moisture-containing indoor air conditions was confirmed to depend on chemisorption in the following reaction pathway: R1–R3(K 2 CO 3 (s) + H 2 O (g) + CO 2 (g) ⇋ 2KHCO 3 (s) (R1), K 2 CO 3 (s) + 1·.5H 2 O(g) ⇋ K 2 CO 3 ·1·.5H 2 O(s) (R2), K 2 CO 3 ·1·.5H 2 O(s) + CO 2 (g) ⇋ 2KHCO 3 (s) + 0·.5H 2 O(g)(R3)). The adsorption working capacities of the recycled BP-K adsorbents were remained relatively constant during four consecutive cycles. [ABSTRACT FROM AUTHOR]