Experimental study on CO2 capture by KOH-activated pistachio shell char and its composites using chemisorption approach

In the present article, the waste pistachio shell is utilized as precursor material to synthesize activated carbon and composites for CO₂ capture on account of its high carbon and low ash content. A two-step optimization strategy for the production of activated carbon is employed to ensure the optimum findings. The synthesization of pistachio shell-derived activated carbon (PSAC) includes carbonization at 500–700°C temperature followed by a KOH activation with varying fraction ratios of biochar: KOH in the range of 1:2–1:6 at 850°C under the inert environment. The optimized carbonized product is found to be at 562.5°C based on the biochar throughput and percentage stable carbon content, considering the effect of moisture content, the molecular mass of carbon and hydrogen, and the H/C ratio in their expressions. Six different composites are also synthesized by varying the fractions of expanded graphite and polyvinyl alcohol. The maximum specific surface area for PSAC is found to be 703 m²/g with micro- and meso-pores, and the greatest CO₂ capture capacity through chemisorption alone reaches 0.858 mmol/g at 1 bar. However, adding ingredients to activated carbon to form composites reduces the specific surface area, leading to lower CO₂ capture capacity due to partial occupation of adsorption sites. A comparative analysis demonstrates that the proposed biomass-derived carbon exhibits superior potential for CO₂ capture, outperforming many sorbents reported in the literature. Additionally, a brief economic analysis is performed on the newly synthesized activated carbon and composite, highlighting their potential for cost-effective CO₂ capture applications.