Enhanced adsorption of heteroatoms-containing volatile organic compounds on single-atom aluminum-modified activated carbon

For the adsorptive removal of polar heteroatom-containing volatile organic compounds (VOCs) from the air, the polar groups of the adsorbents allow for enhanced adsorption forces, however, they also facilitate the competitive adsorption of the coexisting water. Therefore, the design of adsorbents for polar VOCs requires a rational trade-off between adsorption forces and moisture resistance. In this work, activated carbon (AC) was modified by single-atom Al using an adsorption method, and the adsorption performances for some oxygenated and chlorinated VOCs were studied. Compared to AC, the adsorption capacities of the single-atom Al-modified AC for methanol, ethanol, dichloromethane, and 1,2-dichloroethane increased by 45 %, 11 %, 9 %, and 10 %, respectively, under dry conditions, and by 31 %, 13 %, 9 %, and 9 %, respectively, at a relative humidity of 60 %. In contrast, modifying AC by particulate Al species using an impregnation method led to decreased adsorption performances under humid conditions. Density functional theory computations demonstrated that the Al atoms coordinated to functional groups of AC feature particularly high adsorption energies for the polar VOCs, and the hydroxyl groups bonded to the Al atoms also serve as additional adsorption sites. On particulate Al species, the densely populated hydroxyl groups favor the adsorption of water molecules through intensified hydrogen bonding, promoting the rapid formation of water clusters and severely blocking the adsorption sites for VOCs. Such a negative effect on VOCs adsorption can be mitigated on atomically dispersed Al species. The single-atom Al-modified AC can be a readily available adsorbent for the emission control of polar VOCs.