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

Abstract

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.