Mechanism of efficient adsorption for arsenic in aqueous solution by zeolitic imidazolate framework‑8

Arsenic (As) is one extremely hazardous and carcinogenic metalloid element. Due to mining, metal smelting, and other human activities, the pollution of water (especially groundwater) and soil caused by As is increasingly serious, which badly threatens the environment and human health. In this study, a zeolite imidazolate framework (ZIF-8) was synthesized at room temperature and employed as an adsorbent to facilitate the adsorption of As(III) and As(V) from the solution. The successful synthesis of ZIF-8 was demonstrated by X-ray diffraction (XRD), and scanning electron microscopy (SEM) revealed that its particle size was approximately 80 nm. The adsorption kinetics, adsorption isotherm, solution pH, dose, coexisting ions, and the synonymous elements antimony (Sb) were conducted to study the adsorption of As by ZIF-8 nanoparticles. The maximum saturation adsorption capacity was determined to be 101.47 mg/g and 81.40 mg/g for As(III), and As(V) at initial pH = 7.0, respectively. Apparently, ZIF-8 had a good removal effect on As, and it still maintained a good performance after four cycles. The coexisting ions PO₄^3- and CO₃^2- inhibited the adsorption of both As(III) and As(V). ZIF-8 performed well in removing both As and Sb simultaneously, although the presence of Sb hindered the adsorption of both As(III) and As(V). Both FTIR and XPS indicated the adsorption mechanism of As on ZIF-8: ZIF-8 generates a large amount of Zn-OH on the surface through hydrolysis and partial fracture of Zn-N, both of which form surface complexes with As.