Functionalized metal-organic framework UIO-66 nanocomposites with ultra-high stability for efficient adsorption of heavy metals: Kinetics, thermodynamics, and isothermal adsorption

This work reports an easily prepared, reusable and novel ethylenediamine tetramethylene phosphonic acid (EDTMP)-modified defective UIO-66-based metal-organic framework (MOF) for the removal of heavy metals especially Pb(II) from wastewater. The adsorption process was determined by batch experiment. The synthesized materials were evaluated by advance characterization techniques including SEM, FTIR, XRD, TGA, XPS and elemental mapping analyses and the effect of reaction conditions on the adsorption process was evaluated. Results showed that the maximum adsorption capacity of UIO-66-EDTMP for Pb(II) was 381.195 mg/g, achieved at equilibrium time of 480 min at pH 5 and temperature 298 K, respectively. Langmuir, Hill, R-P and Sips isotherms and Pseudo second order (PSO) kinetic models well describes the adsorption process via multi-molecular, irreversible, and chemical adsorption process. Experimental and mechanistic tests have shown that the treatment of Pb by UIO-66-EDTMP consists mainly of chelation, ion exchange, electrostatic, and interactions between O, N, and P-containing groups. In addition, UIO-66-EDTMP showed better selectivity for Pb(II) compared to the treatment of Cd(II), Cu(II), Zn(II) and Ni(II) under coexistence and good reproducibility in five adsorption cycles. This work would serve as blueprint for further research into post-functionalized MOF materials for heavy metals removal from water.