Mechanistic effects of graphitization degrees and surface oxygen heteroatoms on VOCs adsorptive separation: Experimental and theoretical perspective

Abstract

The porous carbon is considered to be one of the most suitable materials for volatile organic compounds (VOCs) adsorption and separation. Revealing the adsorption behavior and molecular interaction mechanism is of great significance for the preparation and synthesis of porous carbon adsorbents. Herein, we investigated detailed mechanistic effects of graphitization degrees and surface oxygen heteroatoms of porous carbon on their benzene and ethanol adsorptive separation performance by combining experiments and theoretical calculations. The results show that graphitized carbon surface has a stronger van der Waals interaction with benzene molecules compared to the disordered carbon surface, and thus exhibit a higher benzene adsorption performance and benzene/ethanol selectivity. While the introduction of oxygen functional groups enhances electrostatic affinity of porous carbon surface, resulting in higher ethanol adsorption capacity and ethanol/benzene selectivity under the entire pressure range. Subsequent theoretical calculations studied the adsorption behaviors of benzene and ethanol molecules in porous carbon models (with different graphitization degrees and oxygen contents) from the perspective of the weak interactions, and found the different molecular configurations of benzene and ethanol is the main leading cause of their different adsorption preferences. This study provided mechanistic insights on how the graphitization degrees and oxygen heteroatoms affected the capture and separation properties of porous carbon, which would further provide a rational alternative strategy in the preparation and synthesis of porous carbons for the effective gas mixture capture and separation.