Superior pore size for enhancing the competitive adsorption of VOCs under high humid conditions: An experiment and molecular simulation study

Water vapor greatly decreases the adsorption capacity of activated carbons (AC) for low-concentration volatile organic compounds (VOCs) under high humid conditions. However, the design and synthesis of AC with high adsorption selectivity for VOCs/water vapor still remains a challenge. In this paper, a hydrophobic hierarchical porous AC was synthesized by using g-C3N4 as the pore-forming agent and the roles of pore sizes on the competitive adsorption were studied by experiments and simulation calculations. The results showed that pore size of 0.59–1.50 nm had a stronger correlation with toluene dynamic adsorption capacity. The largest adsorption capacity of single toluene and water vapor occurred in the 1.0 nm and 0.7 nm slit pore, respectively. During the toluene adsorption at 70 RH%, the superior pore size was 0.7–1.30 nm, and the maximum value appeared in the 1.0 nm pore without pore condensation of water clusters. Furthermore, a quantitative relationship that the superior pore size of VOCs at 70 RH% was 0.86–1.52 S (S is the longest distance of VOCs molecule) was summarized. In addition, a lower surface oxidation degree would broaden superior pore size range. This study provides a theoretical preference for designing AC for target VOCs removal from high humid conditions.