Green synthesis of SnO 2 -ZnO-eggshell nanocomposites and study of their application in removal of mercury (II) ions from aqueous solution.

Background: Mercury (Hg) in dental amalgam is the world's hidden source of mercury contamination. The development of more eco-friendly and cost-effective adsorbents to reduce mercury pollutants in wastewater is highly desirable and is still a major challenge. In this study, a novel nanocomposite was synthesized and used as an efficient adsorbent for the removal of Hg(II) ions from aqueous solution.
Methods: A green and cost-effective method was described to the synthesis of SnO ₂ -ZnO-eggshell nanocomposites using teucrium polium extract as a renewable reductant and mild stabilizer. The biosynthesized nanocomposites were characterized by various techniques. The novel SnO ₂ -ZnO-eggshell nanocomposites were used as an effective adsorbent in the removal of mercury (II) ions. To achieve the maximum absorption efficiency of Hg(II) ions, the effect of operating factors such as pH value, the dose of catalyst, the initial metal concentration of Hg(II) ions, and catalyst type were evaluated.
Results: The removal percentage and adsorption capacity of Hg(II) were obtained 99.15% and 396.6 mg.g ^- 1, respectively, under optimal conditions after 5 minutes. The selectivity of SnO ₂ -ZnO-eggshell nanocomposites for the adsorption of metal ions was studied, and the highest selectivity was obtained for adsorption of Hg (II) ions. Furthermore, the SnO ₂ - ZnO-eggshell nanocomposites could be recovered and reused at least three times without considerable loss of their efficiency.
Conclusions: The present approach has advantages such as rapidity, simplicity, selectivity, low cost and, most importantly, the use of nanocomposites containing a bio-waste material of eggshell for removal of Hg(II) ions from aqueous solution.
Competing Interests: Conflict of interestAll authors declare that they have no conflict of interest.
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