Adsorptive removal of diclofenac sodium from water with Zr-based metal–organic frameworks

The adsorptive removal of diclofenac sodium (DCF), one of the most frequently detected pharmaceuticals and personal care products (PPCPs), was studied for the first time with metal–organic frameworks (MOFs). Zr-based MOFs, UiO-66 and functionalized UiO-66s (with SO₃H/NH₂), were applied in the adsorption and the results were compared to that of activated carbon (AC). The pristine and functionalized UiO-66s showed much better performances than AC in terms of both the adsorption kinetics and capacities. The faster adsorption kinetics is significant as the pore size of UiO-66 is smaller than that of AC, which also suggests that certain interactions, such as electrostatic interaction or π–π stacking, might exist between DCF and UiO-66. In addition, the functionalization of UiO-66 with SO₃H groups resulted in a remarkable enhancement of the adsorption kinetics and capacity. However, the opposite trend was found after the NH₂ functionalization of UiO-66. These results suggest that some additional interactions might exist, such as base–base repulsion between the NH₂ group of NH₂-UiO-66 and the NH group of DCF, or acid–base attraction between the SO₃H group of SO₃H-UiO-66 and the NH group of DCF. Furthermore, at low concentrations, the adsorption capacity of the SO₃H-functionalized UiO-66 was approximately 13-times higher than that of AC, which is very important from a practical point of view.