Activated Carbon–Metal Organic Framework Composite for the Adsorption of Contaminants of Emerging Concern from Water

A composite adsorbent (CMOF) based on in situ growth of MIL-100Fe (MOF) within the macro- and mesopores of a Darco-KB-G activated carbon (AC) was prepared for the efficient adsorption of a set of contaminants of emerging concern (CECs), namely, caffeine (CFN), carbamazepine (CBZ), clofibric acid (CA), 10,11-epoxycarbamazepine (Ep-CBZ), naproxen (NPX), o-desmethylnaproxen (o-DMN), paraxanthine (PXN), and salicylic acid (SA), from water. The properties of the composite and that of the parent materials were evaluated via X-ray diffraction, scanning electron microscopy, nitrogen porosimetry, thermal gravimetric analysis (TGA), and X-ray photoelectron microscopy. Mass balances indicate that the composite contains about 46 wt % MOF, while a comparison of pore size distributions and TGA corroborated that the vast majority of the crystalline material resides within the macro/mesopores of the AC. Zeta potential measurements revealed that the acid media used during the in situ growth of the MOF resulted in a CMOF surface charge profile (isoelectric point (IEP) = ∼3.2) that is generally more negative than that of the MIL-100(Fe) (IEP = ∼4.2) and the nonacid treated AC (IEP = ∼5.5). Single and multicomponent CEC equilibrium adsorption tests were performed at room temperature, neutral pH conditions, and low CEC concentrations (∼μg L^–1). Single component adsorption data show that the composite adsorbs 10-fold more CEC molecules compared to the MOF alone, with a selectivity that increases as follows: CA < SA < o-DMN < PXN < NPX < CFN < Ep-CBZ < CBZ. The effect of competition among the CECs on the adsorption capacity of CMOF was not as significant, only about 9% smaller compared to single component adsorption data. Uptake improvements seen in the CMOF appear to be the result of interactions based on a combination of hydrophobicity (from the AC core) and enhanced electrostatic level forces as well as π-complexation and π–π stacking interactions.