Confined space synthesis of chromium–based metal–organic frameworks in activated carbon: Synergistic effect on the adsorption of contaminants of emerging concern from water

Abstract

The steadfast presence of contaminants of emerging concern (CECs) in the environment calls for tailored remediation strategies. In this regard, Cr-based metal-organic frameworks (MOFs; MIL-100Cr and MIL-101Cr) were grown inside of activated carbon (AC) pores via confined synthesis for a superior adsorptive removal of those CECs from water. The composites CMOF-100Cr and CMOF-101Cr, as well as the apohost AC and pure MOFs, were characterized via X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive analysis by X-rays (EDAX), nitrogen adsorption–desorption, thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy, and zeta potential measurements. XRD, SEM/EDAX, TGA, and pore size distribution data provided direct evidence of the successfully confined space syntheses of the hierarchical composites. Occupancy of the large voids of AC by the MOF was 100% and 43% for CMOF-100Cr and CMOF-101Cr, respectively. The adsorption capacity of the materials was evaluated in both single- and multi-component fashion at neutral pH and low CEC concentrations (μg L−1). The CECs were caffeine (CFN), carbamazepine (CBZ), clofibric acid (CA), naproxen (NPX), and metabolites 10,11-epoxycarbamazepine (Ep-CBZ), o-desmethylnaproxen (o-DMN), paraxanthine (PXN), and salicylic acid (SA). In general, the observed capacities for both single and multi-component adsorption of CECs increased as follows MIL-100Cr < < MIL-101Cr < CMOF-101Cr < AC < < CMOF-100Cr. Compared to the composite containing MIL-100Fe (i.e., CMOF-100Fe) previously developed by our group, the substitution of the metal node by Cr3+ produced significant enhancements in CEC uptake capacities. The affinity of CMOF-100Cr toward CECs increases as follow: SA < CA< o-DMN < NPX < PXN < CFN < Ep-CBZ < CBZ. Environmental significanceThe persistence of contaminants of emerging concern (CECs) in water mandates the development of tailored remediation strategies. To be suitable, these must consider efficacy and avoid undesired byproducts. An attempt to individually grow two chromium-based nanoporous metal-organic frameworks, each possessing particular linkers, within the pores of an activated carbon via confined space synthesis has proven to be effective in the adsorptive removal of a set of CECs that included metabolites. Furthermore, the adsorption was conducted in both single- and multi-component fashion to gain insight into the CECs competitive nature during uptake. The hierarchical composite adsorbents exhibited superior uptake capacity because of the synergistic combination of hydrophobicity and specific interactions between the metal node and the CECs, while multiple adsorption cycles were possible via thermal regeneration.