Liquid-Phase Adsorption of Aromatics over a Metal-Organic Framework and Activated Carbon: Effects of Hydrophobicity/Hydrophilicity of Adsorbents and Solvent Polarity

In order to understand the effect of solvent polarity and hydrophilicity/hydrophobicity of adsorbents on adsorption, aromatic compounds with very low acidity or basicity were adsorbed over two highly porous adsorbents, a metal-organic framework (MOF, MIL-101) and activated carbon (AC). Thiophene, pyrrole, and nitrobenzene were tested in liquid-phase adsorptions to estimate possible applications of the adsorbents in adsorptive desulfurization (ADS), adsorptive denitrogenation (ADN), and water purification, respectively. MIL-101 adsorbed the three adsorbates more effectively with decreasing solvent polarity, and AC with increasing solvent polarity. This behavior can be explained by the hydrophilicity of MIL-101 and hydrophobicity of AC, which was confirmed by measuring the hydrophobicity indexes. The preferential adsorptions of the adsorbates over MOF might be explained by polar interactions and AC by hydrophobic interactions. Moreover, it can be concluded that MOFs, especially hydrophilic ones, can be effectively used in adsorptions in nonaqueous phases, including ADS and ADN. Finally, an increase in hydrophobicity of a MOF is necessary for the applications of MOFs in water purification.