Prediction and optimization of removal performance for europium onto phosphate decorated zirconium-based metal–organic framework nanocomposites: Structure-activity relationship and mechanism evaluation

Herein, phosphorylation modified zirconium-based metal–organic frameworks composites (UiO-66-PO 4 ) were synthesized by facile and green approach, which was employed to remove Eu(III) from water solution under various experimental conditions. The macroscopic experiments showed that the removal performance of Eu(III) onto the UiO-66-PO 4 composites was endothermic and spontaneous with the tremendous phosphate groups acting as critical binding sites. The SEM, XRD and FTIR provided beneficial evidence for propitious phosphate group grafted onto UiO-66 surfaces. The removal performance of Eu(III) onto UiO-66-PO 4 composites followed the pseudo-second-order model and the adsorption isotherms were well simulated by Langmuir model. The maximum adsorption capacity of UiO-66-PO 4 composites toward Eu(III) was calculated to 3.86 × 10 -4 mol·g −1 using Langmuir model. The UiO-66-PO 4 hybrids having excellently stable could be easily regenerated with no observed significant reduction in the elimination of Eu(III) even after five consecutive cycles. Furthermore, the XPS spectra results further revealed that those including zirconium, phosphate and oxygen functional groups played significantly role in the restricting of europium onto UiO-66-PO 4 surfaces. The experimental results further illustrated that the interactive mechanisms of Eu(III) onto UiO-66-PO 4 hybrids were primarily attributed to the outer-sphere surface complexation at low pH values and then inner sphere surface complexation at high pH values. Based on the discussed results, the UiO-66-PO 4 composites can be as promising candidates with favorably recycled reutilization for the elimination of europium from wastewater systems.