Zeolitic Imidazolate Framework-8 with High Efficiency in Trace Arsenate Adsorption and Removal from Water

The development of highly efficient adsorbents, especially those aimed at the capture of trace (ppb, 10–9) arsenate, is one of the principal challenges in the water treatment field. In this article, zeolitic imidazolate framework-8 (ZIF-8) was explored for the removal of trace arsenate from water. Results showed that ZIF-8 outperformed some other adsorbents and owned the first and highest reported adsorption capacity (76.5 mg g–1) at a low equilibrium concentration (9.8 μg L–1). Satisfactory adsorption properties (adsorption capacity, adsorption rate, adaptability to water environment, regeneration capacity) demonstrated the feasibility of using ZIF-8 as an efficient adsorbent for the removal of aquatic trace arsenate. In addition, Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) spectra revealed the proposed mechanism of As(V) adsorption onto ZIF-8: producing large amounts of external active sites (Zn–OH) through the dissociative adsorption of water and subsequently forming an inner-sphere complex with the arsenate molecule. Insights into the adsorption process uncovered the key factors to the formation of this high removal efficiency: the hydration process to form a surface hydrogen group by dissociative adsorption of water; the high accessible surface area; and the cooperative interaction (e.g., van der Waals' force and hydrogen bonding) between As(V) species at low surface coverage.