Copper-doping induced hierarchically porous metal-organic framework for enhanced adsorption of cefradine antibiotic

Development of hierarchically porous materials is important for adsorptive removal of antibiotic with large molecular size. Herein, we proposed a novel strategy for constructing hierarchically porous metal-organic frameworks (MOFs), via introducing low-coordination-number copper in zirconium-oxygen clusters. Compared with UiO-66 (UiO, University of Oslo), the Cu-doped sample exhibits larger specific surface area and importantly, abundant defects and large rhombus-like window. Benefited from that, cefradine is easily diffused into the cages of UiO-66. The resultant UiO-66-Cu owns much higher adsorption capacity (325.1 mg g−1) for this antibiotic than Cu-absence sample does (102.0 mg g−1), which is also superior to those reported adsorbents. Besides, adsorption equilibrium was obtained at ∼600 min. It is found that the adsorption behavior can be well described by Langmuir isotherm model and pseudo-second-order model. The adsorption is gradually enhanced along with the increasing pH (2.0–8.0). Co-existing ions including Na+, K+, Ca2+, Mg2+, Cl-, NO3- and SO42- commonly have negligible effects on the adsorption. Finally, the adsorbent can be well regenerated by using ethanol as the eluent. Mechanism investigation indicates that cefradine adsorption in UiO-66-Cu is driven by electrostatic, hydrogen bond and coordination interactions. Thus, our work provides an effective adsorbent for cefradine and meanwhile proposes a new approach to construct hierarchically porous MOFs.