Ethylenediamine-functionalized Zr-based MOF for efficient removal of heavy metal ions from water

Ethylenediamine-functionalized Zr-based metal-organic framework (MOF, UiO-66-EDA) was prepared via Michael addition reaction to investigate its potential for adsorption of heavy metal ions from water. Specifically, the influence of agitation time, solution pH, the dosage of the adsorbent, initial metal ion concentration, temperature, and coexistence of other metal ions was investigated on the removal efficiency of UiO-66-EDA towards Pb(II), Cd(II), and Cu(II) metal ions. The pseudo-second-order kinetic model governed the adsorption of these ions onto the UiO-66-EDA. Langmuir isotherm model matched the experimental isotherm of adsorption with a maximum adsorption capacity of 243.90, 217.39, and 208.33 mg/g for Pb, Cd, and Cu ions, respectively. The adsorption of Pb, Cd, and Cu ions onto UiO-66-EDA was dependent on electron exchange, electron sharing, electrostatic and covalent interactions between the metal ions as well as the abundant functional groups on UiO-66-EDA surface. Thermodynamic parameters such as free energy changes (ΔG), standard enthalpy changes (ΔH), and standard entropy changes (ΔS) were calculated, which revealed spontaneous and endothermic nature of the adsorption process. The UiO-66-EDA was stable and recyclable during adsorption studies of Pb, Cd, and Cu ions, suggesting its potentiality as an adsorbent for heavy metals recovery.