Surfactant-free green synthesis of Fe3O4 nanoparticles capped with 3,4-dihydroxy-phenethylcarbamodithioate: stable recyclable magnetic nanoparticles for the rapid and efficient removal of Hg(II) ions from water

Mercury is considered one of the most notorious global pollutants due to its high toxicity and widespread use in industry. Although many materials have been developed for the removal of mercury for water purification, most of these materials are difficult to reuse, which may lead to an increase in the mercury handling expense. Therefore, new sustainable materials that can be easily recycled and are highly efficient for the removal of mercury are required. Herein, we report the surfactant-free green synthesis of Fe3O4 magnetic nanoparticles (MNPs) using a watermelon (Citrullus lanatus) rind extract. The Fe3O4 MNPs were further functionalized with 3,4-dihydroxyphenethylcarbamodithioate (DHPCT) and applied to the removal of Hg(II). Evaluation of the mercury removal efficiency and the amount adsorbed by DHPCT@Fe3O4 MNPs demonstrated a high Hg(II) removal efficiency (98%) with a maximum Hg(II) adsorption capacity of 52.1 mg g(-1). Systematic studies of the adsorption mechanism and selectivity suggest that the soft ligand (DHPCT) can preferentially coordinate with the soft metal ion (Hg(II)) resulting in selective mercury removal. The developed DHPCT@Fe3O4 MNPs were readily recycled several times using an external magnet by exploiting their ferromagnetic character, without a significant decline in the Hg(II) removal efficiency. This study provides a new insight into the preparation of a highly efficient adsorbent for Hg(II) removal by an eco-friendly method.