The selective adsorption mechanism of benzene over water on nitrogen-doped activated carbon regulated by methyl functional groups

Improving the adsorption capacity of activated carbon (AC) for volatile organic compounds (VOCs) in humid conditions, while suppressing the interference of water molecules on the adsorption process, is significant for maximizing the effectiveness of AC as an adsorbent for efficient VOC removal. This paper investigates the impact of water on benzene adsorption by nitrogen-doped activated carbon (ACN), the hydrophobicity of different nitrogen-doped types, and the effects of methyl on the selective adsorption of benzene by ACN. The investigation is based on experiments and DFT simulations, and the corresponding mechanisms were elucidated through the force field-based energy decomposition analysis (EDA-FF), the independent gradient model based on Hirshfeld partition (IGMH), and the atoms in molecules (AIM). Under the coexistence of benzene and water, a van der Waals (vdW) interaction occurs between the adsorbed water molecules and benzene molecules, which seriously impairs benzene adsorption on ACN. Pyridine and pyrrole N enhance the adsorption of water by increasing the electrostatic interaction between water molecules and AC. Methyl group reduces hydrophilicity by increasing the repulsion of pyridine and pyrrole nitrogen with water. The selective adsorption of benzene on ACN was improved by enhancing the dispersion effect with benzene. The experimental results showed that after ACN modification with the methyl, benzene adsorption was completely restored to the situation when there was no water interference. This confirms that nitrogen-methylation is an effective method for enhancing benzene adsorption by AC while suppressing water interference.