Engineering NSAIDs imprinted UiO-66s for markedly enhanced adsorption of coexisting diclofenac sodium and Cu(II) and their synergistic adsorption mechanism

Abstract Competitive adsorption of complex nonsteroidal anti-inflammatory drugs (NSAIDs) from wastewater often reduces the adsorption capacity of object pollutants on most porous materials. To address this issue, NSAIDs molecules were proposed for engineering imprinted pores in UiO-66s to boost their adsorption capacity towards diclofenac sodium (DCF) and Cu(II) in a complex solution. Naproxen (NAP) with proper chemical structure was proved to introduce more imprinted pores (at ~19 A) with enhanced mesoporous volume, abundant unsaturated metal sites, and terminal hydroxyl groups in UiO-66@NAP. These new intriguing properties awarded high adsorption affinity to UiO-66@NAP for DCF and Cu(II), and their adsorption capacities reached up to 385 and 52 mg/g for single DCF and Cu(II) components, respectively. When DCF and Cu(II) simultaneously appeared in an aqueous solution, DCF was proved to preferentially occupy adsorption sites on UiO-66@NAP with higher adsorption kinetics compared to Cu(II). Afterwards, these pre-adsorbed DCF acted as new adsorption sites to bridge more Cu(II) in the solution. Similarly, the adsorbed Cu(II) on UiO-66@NAP had the same reciprocal bridging effect towards DCF, which realized the synergistic adsorption of DCF and Cu(II) over UiO-66@NAP. Notably, DCF was found to greatly boost the synergistic effect of the Cu(II) adsorption. As a result, UiO-66@NAP exhibited 1.5 and 2.6 times higher uptakes for DCF (573 mg/g) and Cu(II) (135 mg/g) in the binary system compared to their single pollutant system, and its equilibrium adsorption capacity was much higher compared to several state-of-the-art adsorbents. The current work set out a new strategy to modify MOFs for enhanced adsorption of complex NSAID contaminants and revealed a deep understanding of the interactions between NSAIDs and heavy metals ions.