Enhancement of CO 2 adsorption on high surface area activated carbon modified by N 2, H 2 and ammonia

Abstract

The activated carbons (ACs) with high surface area were modified separately by using ammonia aqueous solution impregnation and microwave irradiation in an atmosphere of N 2 or H 2 in order to improve their adsorption properties toward CO 2. The modified ACs were characterized, and the surface chemical properties of the ACs were determined separately by FTIR, Boehm titration and X-ray photoelectron spectroscopy (XPS) methods. The isotherms of CO 2 on the modified ACs were measured. Results showed that after surface modification, the contents of elements C and N of the samples increased, while that of the element O of the samples decreased in comparison with the original AC. Correspondingly, the amounts of the surface basic groups of the modified ACs increased, while those of the surface acidic groups decreased as compared to the original AC. The use of microwave irradiation in an atmosphere of N 2 to modify the carbon can make the total basic groups of the surfaces of the ACs be the highest among the modified ACs. As a consequence of that, the modified AC samples had higher adsorption capacities of CO 2 than the original AC, and the more the surface basic groups of the ACs, the higher the adsorption capacity of the ACs for CO 2. The amount adsorbed of CO 2 on the modified AC by the microwave irradiation in the atmosphere of N 2 was up to 3.75 mmol/g at 1 atm and 293 K, having an increase of 28% in comparison with the original AC.