A novel metal-organic framework-derived ZnO@ZIF-8 adsorbent with high efficiency for Pb (II) from solution: Performance and mechanisms

A metal-organic framework (ZnO@ZIF-8) with great adsorption potential was developed using ZnO nanoparticles as a surface-active center and applied to lead removal from wastewater. The adsorption experiments were carried out and the related adsorption behaviors were investigated. The adsorbent shows excellent adsorption performance between pH 3-5. The maximum adsorption capacity of ZnO@ZIF-8 for Pb (II) was 689.36 mg/g at 303 K. The adsorptive process of Pb (II) onto ZnO@ZIF-8 conforms to the Langmuir isotherm and pseudo-second-order kinetic models. Thermodynamics illustrate that the adsorption process is chemical adsorption on a uniform surface. Selectivity experiments showed that ZnO@ZIF-8 had the strongest affinity with Pb (II). The adsorption-desorption cycle confirmed that ZnO@ZIF-8 was a reliable and recyclable adsorbent. XPS, Zeta potential and FT-IR analysis illustrate that the adsorption of Pb (II) by ZnO@ZIF-8 was concentrated in electrostatic adsorption and chelation. DFT calculation indicated that there are different types of Pb (II) combination mode (Pb-N and Pb-O) and the adsorption mainly depended on the chelation. This study presented herein played important roles in the governance of heavy metal waste-water pollution as a result of ZnO@ZIF-8 can effective selectivity cleanup of Pb (II).