Adsorption of Pd(II) from wastewater by a functionalized metal-organic framework with aminopyridine structure: Performance and mechanism

Metal-organic frameworks are recognized as a new kind of potential adsorbent for wastewater treatment because of their tunable pore size, high surface area and modifiable functionality. In this work, 2,6-diaminopyridine functionalized UiO-66-NH2 (UiO-66-DAP) was synthesized by a post-modification strategy and was applied to the adsorption of Pd(II) from aqueous solution. The aminopyridine structure on UiO-66-DAP greatly improved the adsorption performance for Pd(II), with an adsorption capacity of 190.95 mg/g. The adsorption process of Pd (II) on UiO-66-DAP was consistent with the pseudo-second-order kinetic model and the Langmuir adsorption isotherm. Thermodynamic studies confirmed that the adsorption process was endothermic and spontaneous. Regeneration studies showed that UiO-66-DAP was stable and recyclable. Moreover, UiO-66-DAP could maintain high selectivity to Pd(II) even in a wastewater containing multiple interfering metal ions. According to the results of Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), zeta potential, comparative experiments and DFT calculations, the chelation and electrostatic attraction between Pd(II) and the aminopyridine structural unit are the dominant mechanisms. Using UiO-66-DAP as an adsorbent, this study provides a promising way for the separation of palladium form wastewater.