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

Abstract

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