Carbon–based metal organic framework composite adsorbent for the removal of contaminants of emerging concern from water

Abstract

For more than two decades, the presence of contaminants of emerging concern (CECs) in sources of water has attracted attention from the scientific community due to their inherent capability to produce biological undesirable effect in living organisms and the overall impact to the environment, even at very low doses. Effective remediation of CECs also remains a challenge, even with current improvements in capacity of water treatment (WT) operations to mitigate pathways associated to the exposition to humans, animals, and edible plants. Therefore, there are significant opportunities in diverse WT areas to enable CEC remediation technologies that would allow for the attainment of higher clean water standards and also to prevent further potential environmental impact. This work offers a promising alternative to remove very low concentrations of CECs from water using composites adsorbents (CMOFs) based on the confined space synthesis of metal organic frameworks (MOFs) inside of activated carbon (AC) pores. This arrangement could offer a synergistic effect produced by the superior hydrophobicity from AC, which is providing not just hydrophobic interactions, but also an effective barrier to diminish water competition for the adsorption active sites given by the MOFs. The resulting CMOFs composite materials were tested in the removal of a specific target of CECs from water in both single- and multi-component matrix. These CECs were chosen not only by their occurrence in the environment, but also exhibit a considerable range of molecular structure and physio-chemical properties, and these include carbamazepine (CBZ), caffeine (CFN), naproxen (NPX), clofibric acid (CA), and metabolites such as salicylic acid (SA), 10,11-epoxycarbamazepine (Ep-CBZ), paraxanthine (PXN), and o-desmethylnaproxen (o-DMN). The latter three result from partial decomposition of primary molecules CBZ, CFN, and NPX, respectively. In addition, this work also evaluated the effect of the chemical environment constitution (i.e., organic linker and metal node) of the MOF over the affinity toward CECs. The obtained results showed that the overall adsorption capacity for the tested materials increases as follow: MIL-100Fe < MIL-100Cr < MIL-101Cr < CMOF-101Cr < AC-treated with acids < CMOF-100Fe < AC < CMOF-100Cr. These results have proven that getting simultaneous hydrophobicity and available active adsorption sites has a tremendous impact in the adsorption capacity of CECs specially in those molecules who remain without ionic charge during the process (i.e., CBZ and Ep-CBZ). Finally, this work has also demonstrated a suitable regeneration via thermal treatment to ensure multi cycle adsorption processes without affecting the overall uptake capacity