Investigation of CO₂ Adsorption on Modified Bimetallic Activated Carbon Derived from Apricot Stones

The adsorption of CO₂ was investigated on monometallic and bimetallic activated carbon (PAC) prepared from apricot waste. Metals such as Zn, Ni, Ce, and Cu were impregnated onto PAC at varying ratios. Scanning electron microscopy images revealed grain-like particles and flower-like layers due to the accumulation of the impregnated metals. N₂ sorption analysis (BET) showed an increase in the PAC surface area to 756.95 m²/g after modification with Zn. For the bimetallic adsorbents, the addition of Cu and Ce resulted in surface areas of 753.95 and 731.91 m²/g, respectively. Pore size distribution analysis indicated the presence of micropore channels in the 1-2 nm range for both monometallic and bimetallic adsorbents. CO₂ adsorption tests demonstrated that metal impregnation on the activated carbon surface enhanced CO₂ adsorption capacity. The 0.5Ce/0.5Zn/PAC sample exhibited the highest CO₂ adsorption capacity, reaching 4.25 mmol/g at 0 °C and 2.77 mmol/g of CO₂ at 25 °C. The heat of adsorption for 0.5Ce0.5Zn/PAC ranged from 31.4 to 41.3 kJ/mol, suggesting that CO₂ adsorption is predominantly physical. A two-cycle regeneration test showed a reduction in CO₂ uptake ranging from 5.1 to 9.7%, indicating high adsorbent stability. The 0.5Ce0.5Zn/PAC adsorbent also demonstrated high selectivity for CO₂ over N₂. Kinetic studies indicated that the intraparticle diffusion model best fits the experimental data. The CO₂ capture system developed in this study shows potential for applications in CO₂ capture at the outlets of production processes and in gas purification facilities.