Hydrophobic carbon with hollow and hierarchical porous structures for efficient VOCs removal from complex exhaust gases: Experiments and DFT calculations

Water vapor and SO2 significantly diminish the adsorption performance of activated carbon (AC) for volatile organic compounds (VOCs) in exhaust gases. In this paper, a hydrophobic and hollow hierarchical porous activated carbon (HHRCs) was synthesized. The HHRC-8 possessed an ultra-high specific surface area (3373.5 m2/g), high mesopore proportion (47.33 %), and low O content (5.19 %). Under dry conditions, HHRC-8 exhibited excellent dynamic and static adsorption capacities both for weak-polar toluene and strong-polar 1,2-dichloroethane, superior to many reported MOFs and carbon materials. Additionally, the static adsorption capacity of water vapor on HHRC-8 was 6.1 mmol/g at 70 RH%, presenting a higher hydrophobicity index. During the competitive adsorption between toluene and 1,2-dichloroethane, HHRC-8, with a substitution peak phenomenon of 1,2-dichloroethane, displayed a higher total adsorption capacity and a longer breakthrough time in complex waste gases. Single water vapor (70 RH%) or SO2 (200 mg/m3) had a negative impact on VOCs adsorption, among which, water vapor showed a greater influence on the adsorption capacity, while SO2 showed a greater effect on breakthrough time. When water vapor and SO2 coexisted, the negative impact superimposed, showing a greater effect on 1,2-dichloroethane. Density functional theory calculations revealed that surface functional groups could interact with water, SO2, 1,2-dichloroethane and toluene molecules. In addition, water vapor and SO2 could mutually promote adsorption through hydrogen bonds. HHRC-8, with hydrophobicity and hierarchical adsorption properties, exhibiting a superior competitive adsorption capacity and an excellent reusability, is a promising adsorbent for the multi-component VOCs removal in complex waste gas.