Chemical modification of activated carbon monoliths for CO2 adsorption

The development of materials with potential application for CO2 capture is a topic of great scientific interest. Activated carbons (AC) can be conveniently used as CO2 adsorbents thanks to their microporous structure and tunable chemical properties. In this work, two AC honeycomb monoliths were synthesized starting from African palm stones through activation either with H3PO4 or with ZnCl2 solution. Surface functionalization was performed in order to add nitrogen groups, aiming at an enhancement of CO2 adsorption capacity. This chemical modification was performed either with ammonia in gas phase or a with 30 % ammonium hydroxide aqueous solution on both AC monolith samples. The original and modified monoliths were characterized by N-2 adsorption at 77 K, infrared spectroscopy, Boehm titration, and immersion calorimetry in benzene and water. CO2 adsorption on both raw and functionalized AC monoliths was evaluated in volumetric equipment at a temperature of 273 K and until 1 bar, and adsorption capacity ranging between 120 and 220 mg(CO2) g (AC) (-1) was obtained. The experimental results indicated that both methods of chemical modification determined an increase in the content of superficial nitrogen groups and thus an increase in CO2 adsorption capacity, the treatment with ammonium hydroxide being slightly preferable.