CO2-assisted synthesis of graphitic resin-based activated carbon for ultrahigh selective adsorption of VOCs under humid conditions

Abstract

Water vapor in the waste gases greatly reduce the VOCs adsorption capacity of adsorbents due to the competitive adsorption. Though chemical activation combined with catalytic graphitization was an available strategy for achieving both good graphitization and rich porosity to capture VOCs under humid conditions, it still remains a challenge of catalyst deactivation. This work developed a novel route to synthesize graphitic resin-based activated carbon (GRC) via CO2-assisted Fe-catalyzed graphitization and concurrent KOH activation. The selective adsorption behaviors of VOCs/water vapor were thoroughly investigated by static and dynamic adsorption experiments. The obtained GRC-10-A (5) displayed an outstanding graphitization degree, lower O content and hierarchical pore structure. This triggers a high dynamic adsorption capacity and a faster intra-particle diffusion both for toluene and 1,2-dichloroethane. For weak polar toluene, the adsorption selectivity quantized by Difference of Isosteric Heats equation was up to 69, exceeding strong polar 1,2-dichloroethane up to 12. Grand Canonical Monte Carlo simulations were used to explore the competitive adsorption mechanism from the perspective of surface oxygen groups (SOG) and pore size. The results revealed the main contributor to the excellent adsorption selectivity was a lower SOG content, which restricted the formation and pore condensation of water clusters. On the other hand, both the micropore overlap potential and molecular kinetic diameter determined the advantageous pore size ranges for different VOCs under humid conditions. These findings provide support for the fabrication and practical application of adsorbents in VOCs removal from humid conditions.