Synthesis of porous and activated carbon from lemon peel waste for CO2 adsorption

The concentration of CO2 in the atmosphere has been increasing and is soon to reach a threatening level for life on the planet. Porous carbons made from biobased materials including from waste resources can be applied to selectively adsorb CO2 from large industrial sites and then lower atmospheric CO2 emissions. In this work, we synthesized highly porous carbons from lemon-peel wastes using two-step activation process involving hydrother-mal carbonization followed by chemical activation with KOH, and KOH + alum at 800 degrees C. The sample activated with KOH + alum has the highest BET surface area (2143 m 2 /g) and total pore volume of 1.3 cc/g. Although the KOH activated sample has a lower surface area (1113 m 2 /g), it has better CO2 adsorption capacity ranging up to 4.5 mmol/g because of its well-developed pore structures and a high proportion (90 %) of micropore dis-tributions. The isosteric heat of adsorption lower than 40 kJ/mol indicated that adsorption is mainly driven by physisorption. Better CO2/N2 selectivity suggested a high affinity of the activated carbons towards CO2. Partic-ularly, the sample activated with KOH had selectivity in the range of 20 at the highest adsorption temperature (40 degrees C), making it a potentially viable option for direct CO2 adsorption applications from large industrial sources.