Metallothionein-immobilized silica-coated magnetic particles as a novel nanobiohybrid adsorbent for highly efficient removal of cadmium from aqueous solutions

Abstract

In this contribution, magnetic nanocomposite particles of Fe₃O₄ cluster@SiO₂ (MNPs) were functionalized with N-(2-aminoethyl)-3-aminopropyltrimethoxy-silane (EDS) to obtain amine-functionalized magnetic nanocomposite particles (AF-MNPs). Then, a novel nanobiohybrid magnetic adsorbent was developed by immobilization of the recombinant form of a rice metallothionein (MT) isoform onto the surface of the synthesized AF-MNP (MT-AF-MNPs) for the highly efficient removal of cadmium ions from aqueous media. The kinetic data for both AF-MNPs and MT-AF-MNPs were best fitted to the pseudo-second-order kinetic model. The best interpretation for the equilibrium data was given by a Langmuir isotherm, and the maximum cadmium adsorption capacities for AF-MNPs and MT-AF-MNPs were 320 mg g⁻¹ and 476 mg g⁻¹, respectively. The adsorption process for both nanocomposite particles was pH dependent and the adsorption capacity was found to decrease with decreasing of the pH. The cadmium-loaded adsorbents could be recovered readily by magnetic separation and regenerated easily by acid treatment. The continuous adsorption–desorption studies indicated that the AF-MNPs and MT-AF-MNPs retain 70% and 56% of their initial adsorption capacity after four adsorption–desorption cycles, respectively. The findings of the present work show the great potential of MT-AF-MNPs as an effective and recyclable adsorbent for the removal of cadmium ions from waste water.