Revealing the role of hierarchical pore in alleviating competitive adsorption between different-sized VOCs: A mechanistic study using coal-based activated carbon with tunable porous hierarchy

Volatile organic compounds (VOCs) are important sources of air pollution complex in China and exist as mixtures of different-sized components in industrial exhaust gases. Activated carbon is a type of widely-used adsorbent for VOCs removal, but faced with poor VOCs co-adsorption performance due to competitive adsorption. Herein, an efficient strategy of constructing hierarchical pore configuration was proposed to alleviate competitive adsorption of VOCs with different kinetic diameters and further enhance co-adsorption capacity. The role of hierarchical pore configuration in co-adsorption of typical VOCs toluene and dichloromethane was revealed based on coal-based porous carbon with tunable pore hierarchy. Dynamic adsorption experiments show that microporedominant carbon, adsorption capacities of toluene and dichloromethane under co-adsorption dramatically decreased by 14 % and 42 % respectively compared to single component adsorption. However, the loss of adsorption capacity within the hierarchical porous carbon was only 9 % and 14 % under the same conditions. Correlation analyses and molecular dynamics simulations showed that hierarchical porous carbon could induce unique adsorption behavior in which toluene tends to be stored in mesopore and dichloromethane is mainly distributed in micropore, thus effectively reducing the competitive adsorption. Guided by the found mechanism, we further prepared hierarchical porous carbon with high specific surface area and pore volume, based on which adsorption capacity of toluene and dichloromethane under co-adsorption condition was enhanced by more than 50 % compared to micropore-dominant carbon. The relevant mechanism provides a theoretical basis for advancing the optimization of co-adsorption process of mixed VOCs.