Synthesis and Characterization of Activated Biocarbons Produced from Avocado Seeds Using the Non-Toxic and Environmentally Friendly Activating Agent K2CO3 for CO2 Capture

Activated biocarbons were synthesized from avocado seeds using potassium carbonate as an activating agent. The study aimed to evaluate K2CO3 as a greener and less corrosive alternative to KOH, traditionally used for producing porous carbons. Twelve samples were obtained under varying activation conditions using both dry K2CO3 and its saturated solution. The material activated at 800 °C with a 1:1 precursor-to-activator ratio (C_K2CO3_800) showed the highest CO2 adsorption capacity of 6.26 mmol/g at 0 °C and 1 bar. Nitrogen adsorption–desorption analysis confirmed a predominantly microporous structure, with ultramicropores (0.3–0.7 nm) primarily responsible for the high CO2 uptake. The Sips model provided the best fit to the adsorption equilibrium data, indicating a heterogeneous surface. The isosteric heat of adsorption (22–26 kJ/mol) confirmed a physical adsorption mechanism. Furthermore, the CO2/N2 selectivity, evaluated using the Ideal Adsorbed Solution Theory (IAST), reached values up to 18 at low pressures, highlighting the excellent separation performance. These findings demonstrate that avocado seed-derived activated carbons prepared with K2CO3 are efficient, renewable, and environmentally friendly sorbents for CO2 capture, combining high adsorption capacity with sustainability and ease of synthesis.