Defective NH2-UiO-66 for effective Pb(II) removal: Facile fabrication strategy, performances and mechanisms

Abstract

Defective NH₂-UiO-66 adsorbent (named as NH₂-UiO-66-SD) was successfully fabricated via post-synthesis method with the aid of both sodium carbonate anhydrous (Na₂CO₃) and diethylenetriaminepentaacetic acid (DTPA), in which the defective structure was confirmed by various characterizations. The as-obtained defective NH₂-UiO-66-SD exhibited outstanding Pb(II) sorption capacity (172.21 ​mg ​g⁻¹) and rapid diffusion rate (29.87 ​mg ​g⁻¹ min^−0.5) at room temperature with optimal pH being 5.47. The Pb(II) sorption behavior was conformed to pseudo-second-order kinetics and Langmuir model, demonstrating that the chemical sorption of the monolayer played a dominant model. As well, the thermodynamic parameters like standard Gibbs free energy change ΔG^o (−31.21 ​kJ ​mol⁻¹), standard enthalpy change ΔH^o (12.79 ​kJ⁻¹ ​mol⁻¹) and standard entropy change ΔS^o (146.73 ​J ​mol⁻¹ ​K⁻¹) revealed that the Pb(II) sorption process of NH₂-UiO-66-SD was spontaneous, endothermic and disordered. Furthermore, the NH₂-UiO-66-SD exhibited desirable desorption and recirculation performances (removal efficiencies >85 ​% in 5 runs) with ideal stability. Moreover, the Pb(II) sorption mechanism of NH₂-UiO-66-SD mainly included the electrostatic attractions and coordinative interactions. Overall, this work offered an intriguing method of fabricating defective NH₂-UiO-66 adsorbent, which vastly enhanced adsorption efficiency for toxic metal ions elimination from wastewater.