Simultaneous removal of antibiotics and metal oxoanions from aqueous solution by Ce-doped UiO-66: Removal mechanisms and solid phase extraction

Abstract

Simultaneous removal of coexistent antibiotics and heavy metals from wastewater is crucial for the safety and quality of aquatic ecosystems. Metal-organic frameworks (MOFs) are promising candidates for wastewater remediation due to their robust and tailorable pore structure, but the removal mechanisms for the synchronous removal of multiple pollutants remain unclear. Herein, Ce-doped UiO-66 (Ce-UiO-66) was prepared and utilized to efficiently remove multiple pollutants from water under single and mixed pollutant systems. After Ce doping, the adsorption amounts of pefloxacin (PEF), tetracycline (TC) and Cr(VI) reached 476.3 mg/g, 368.6 mg/g and 58.3 mg/g, respectively, which were 5–10 times higher than those of pristine UiO-66. In the binary system, the presence of Cr(VI) broadened the optimal adsorption pH range of PEF, and Cr(VI) adsorption was enhanced in the presence of low concentrated PEF. Various interactions contributed together to the excellent adsorption ability of Ce-UiO-66. The contribution degree of some interactions was as follows: (1) for PEF adsorption, at 2.0 < pH < 5.0, complexation bonding (CB) accounted for 40–95% of the total uptake; at 5.0 < pH < 10.0, the contribution of electrostatic attraction (EA) increased to approximately 5–36% while CB decreased to 32–50%; (2) for TC adsorption, at 2.0 < pH < 7.0, CB accounted for 50–81% of the total uptake; at 7.0 < pH < 10.0, the contribution of CB increased to approximately 30% and EA at 2.0 < pH < 10.0 accounted for 5–14% of the total uptake; and (3) for Cr(VI) adsorption, at 2.0 < pH < 10.0, EA and CB dominated the adsorption, together accounting for 50–100% of the total uptake. More importantly, the order of functional groups participating in adsorption was revealed by 2D-FTIR-COS analysis. Ce-UiO-66 showed excellent recycling ability and was efficient in removing multiple pollutants from various actual water samples. Moreover, simple solid phase extraction (SPE) experiments revealed that Ce-UiO-66 obtained excellent adsorption capacities of 474.63 mg/g and 261.8 mg/g for PEF and TC, respectively. This study provides a new paradigm for devolving highly robust adsorbents for wastewater treatment.