Simultaneous defect engineering and phosphoric acid functionalization of UiO-66 for enhanced adsorption of Yb(III)

The recovery of rare earth elements from mineral wastes is extremely critical for the soaring global demand due to their unique roles and resource scarcity. In this work, the defective phosphoric acid functionalized UiO-66-COOH (UiO-66-COOH-OP-ST2) was prepared via the successive phosphoric acid functionalization and defect modulation procedures towards UiO-66-COOH. The adsorption results disclosed that maximal adsorption capacities of UiO-66-COOH-OP-ST2 and phosphoric acid functionalized UiO-66-COOH (UiO-66-COOH-OP) were found to be 132.76 and 83.11 mg/g at pH = 6, respectively. Adsorption kinetics curves and isotherms revealed that the adsorption process was consistent with pseudo second order kinetic model and Langmuir isothermal model. Furthermore, UiO-66-COOH-OP-ST2 can maintain 91.74 % of initial adsorption capacity after five consecutive adsorption–desorption cycles, and exhibit no significant changes in the XRD patterns, demonstrating an excellent recycling stability. In addition, the adsorption mechanism elucidated that the elevated adsorption performance was mainly attributed to the electrostatic attraction and complex interaction between the O sites and Yb(III) based on EDS and XPS analysis. This work efficiently improved adsorption performance of metal organic frameworks after simultaneously grafting functional groups and creating defective sites without affecting their stabilities.