The chemical stability of metal-organic frameworks in water treatments: Fundamentals, effect of water matrix and judging methods

Metal-organic frameworks (MOFs), with high surface areas and abundant active sites, have been widely studied as adsorbents and catalysts in water treatments. Although some MOFs are water stable, they do not always keep their stability in water treatments, because MOFs would face threats from not only water but also the water matrix related factors, such as pH, inorganic ions, metal ions and reactive oxygen species. Thus, it is meaningful to have insight into the relationship between MOFs stability and water matrix. However, a lot of studies have reported the excellent performances of MOFs in water treatments, but few ones have deeply revealed the instability of MOFs. In addition, overestimation of MOFs stability might occur, because the commonly used judgment methods of MOFs stability have their disadvantages. Taking the X-ray diffraction (XRD) pattern as an example, partial loss of metal ions and ligands would not result in the obvious change in the XRD pattern of MOFs. Hence, this review pays attention to the fundamentals of MOFs stability, the chemical stability of MOFs in water treatments and judging methods of MOFs stability. Overall, this review is expected to guide a comprehensive understanding of MOFs stability in water treatments, and further help to select suitable MOFs according to the application environments.