A review on the synthesis and applications of green rust for environmental pollutant remediation

Abstract

This paper discusses the various approaches to the synthesis of green rust. Green rusts are synthesized by changing the average oxidation state of iron compounds so that the ratio of ferric/ferrous ions is between 0.25 and 0.33. This can be achieved by mixing ferrous and ferric hydroxides, oxidation of ferrous compounds or reduction of ferric compounds. Characterization of the samples with analytical methods such as Mossbauer spectroscopy, X-ray diffraction spectroscopy, scanning electron microscopy, transmission electron microscopy and atomic-force microscopy is discussed. Green rusts have a layered double hydroxide structure, with an interchangeable anion layer and a mixed ferrous–ferric cation layer. This structure can adsorb ions by intercalation or exchange anions with its environment. The cation layer can oxidize, which gives a reducing nature to green rusts. These properties make them excellent candidates for the reduction and immobilization of several inorganic pollutants. Green rusts also have applications in dechlorination of organic compounds and in the synthesis of nanohybrid materials. These environmental and nanochemistry applications are also covered in this paper.