An environmentally benign synthesis of Fe3O4 nanoparticles to Fe3O4 nanoclusters: Rapid separation and removal of Hg(II) from an aqueous medium.

In the field of nanotechnology, nanoadsorbents have emerged as a powerful tool for the purification of contaminated aqueous environments. Among the variety of nanoadsorbents developed so far, magnetite (Fe3O4) nanoparticles have drawn particular interest because of their quick separation, low cost, flexibility, reproducibility, and environmentally benign nature. Herein, we describe a new strategy for the synthesis of Fe3O4 nanoclusters, which is based on the use of naturally available edible mushrooms (Pleurotus eryngii) and environmentally benign propylene glycol as a solvent medium. By tuning the temperature, we successfully convert Fe3O4 nanoparticles into Fe3O4 nanoclusters via hydrothermal treatment, as evidenced by transmission electron microscopy. The Fe3O4 nanoclusters are functionalized with an organic molecule linker (dihydrolipoic acid, DHLA) to remove hazardous Hg(II) ions selectively. Batch adsorption experiments demonstrate that Hg(II) ions are strongly adsorbed on the material surface, and X-ray photoelectron and Fourier transform infrared spectroscopy techniques reveal the Hg(II) removal mechanism. The DHLA@Fe3O4 nanoclusters show a high removal efficiency of 99.2 % with a maximum Hg(II) removal capacity of 140.84 mg g-1. A kinetic study shows that the adsorption equilibrium is rapidly reached within 60 min and follows a pseudo second-order kinetic model. The adsorption and separation system can be readily recycled using an external magnet when the separation occurs within 10 s. We have studied the effect of various factors on the adsorption process, including pH, concentration, dosage, and temperature. The newly synthesized superparamagnetic DHLA@Fe3O4 nanoclusters open a new path for further development of the medical, catalysis, and environmental fields.