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In this paper, zeolitic imidazolate framework‐8 modified by the ethanediamine (NH2‐ZIF‐8) was employed for adsorbing Au (III) and Ag(I) from aqueous solutions. The adsorption capacities of NH2‐ZIF‐8 towards Au (III) and Ag(I) were found to be significantly affected by the pH values of the solution. The adsorption kinetics studies show that NH2‐ZIF‐8 presents a fast adsorption property towards metals, attaining 93% of adsorption equilibrium uptake for Au (III) within the first 30 min. This phenomenon can be ascribed to the coordination interaction between the amino group and Au (III). The thermodynamic data suggest that the adsorption of NH2‐ZIF‐8 towards Au (III) is endothermic process, while that for Ag(I) is exothermic. The maximum adsorption capacities of NH2‐ZIF‐8 toward Au (III) and Ag(I) can be achieved to 357 mg·g−1 and 222.25 mg·g−1, respectively. The metal ions interference results show that Cu (II) and Ni (II) hardly have no interference on Au (III) adsorption in e‐waste containing 1500 mg·l−1 Cu (II),100 mg·l−1 Ni (II) and 10 mg·l−1 Au (III); while for Ag(I), Cd (II) and Zn (II) have little interference on Ag(I) adsorption in the hybrid solutions containing Ag(I), Ni (II), Cd (II) and Zn (II) with equal concentration (50 mg·l−1), but Ni (II) interference most. The XPS study shows that partial Au (III) was reduced to Au(I), and that Ag(I) was completely reduced to Ag(0) during the adsorption process. The abundant of active sites of NH2‐ZIF‐8 containing C=N, N‐H, and Zn‐OH groups play a key role in the adsorption of Au (III) and Ag(I). In addition, electrostatic interaction can be responsible for the adsorption of Au (III) by NH2‐ZIF‐8. The regeneration experiments results show that the adsorption capacities of NH2‐ZIF‐8 towards Au (III) and Ag(I) can maintain after three cycles. This work provides a reliable method to improve the adsorption kinetics for metal ions.

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Recovery of precious metal ions from wastewater can bring huge economic benefits and alleviate current supply shortage in industries. Here, a novel metal–organic framework (2,5-TP) constructed with sulfur-containing ligands and Zn­(II) was synthesized as a highly efficient adsorbent to adsorb Au­(III) from water for the first time. Compared with that of the reported adsorbents, 2,5-TP exhibits excellent Au­(III) adsorption performance with the maximum adsorption capacity of 1253.5 mg·g–1 and an adsorption ratio of 97%. Significantly, 2,5-TP has excellent selectivity toward Au­(III) and remarkable recycle performance. The adsorption kinetics for Au­(III) adsorption can be described well by the pseudo-second-order kinetics and the adsorption isotherm data accord well with the Sips model, indicating that the adsorption of Au­(III) onto 2,5-TP is a heterogeneous chemisorption process. The formation of Au–S and Zn–O–Au bonds suggests an important role in Au­(III) adsorption. With the facile synthesis, high adsorption capacity, excellent selectivity, and outstanding reusability, the 2,5-TP adsorbent could be a promising candidate to adsorb Au­(III) from water.

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In this work, an adsorbent, an O-containing metal-organic framework (MOF) (Zn-NDC) was designed and prepared to recover Ag(I) with high performance to alleviate its high consumption and protect the environment. Its adsorption performance was accessed by batch adsorption experiment. The kinetic data fit well with the pseudo-first-order model, pseudo-second-order model, and moving boundary model. It is found that the overall adsorption rate was determined by liquid film diffusion. The maximum adsorption of Zn-NDC towards Ag(I) can be up to 844 mgÁg −1 , superior to many reported adsorbents. Besides, Sips model better fits with the experimental data, implying the adsorption process belongs to heterogeneous adsorption. Thermodynamic analysis indicates the adsorption process of Ag(I) is a spontaneous, exothermic, and entropy-driven process. Zn-NDC could selectively adsorb Ag(I) from a hybrid solution containing Ag(I), Co(II), Ni(II), Cd(II), Cr(III), Zn(II), and Mg(II). Moreover, Zn-NDC could be effectively reused up to three cycles with negligible change in adsorption capacity. Finally, the X-ray photoelectron spectroscopy (XPS) results show the electronic attraction and inner-sphere surface complexation are the main adsorption mechanism. Based on the above analysis, Zn-NDC could be regarded a cost-effective adsorbent for the Ag(I) removal.