ABSTRACT
Maximizing the safe removal of hexavalent chromium (Cr6+) from waste streams is an increasing demand due to the environmental, economic and health benefits. The integrated adsorption and bio-reduction method can be applied for the elimination of the highly toxic Cr6+ and its detoxification. This work describes a synthetic method for achieving the best chemical composition of spherical and flower-like manganese ferrite (MnxFe3-xO4) nanostructures (NS) for Cr6+ adsorption. We selected NS with the highest adsorption performance to study its efficiency in the extracellular reduction of Cr6+ into a trivalent state (Cr3+) by Shewanella oneidensis (S. oneidensis) MR-1. MnxFe3-xO4 NS were prepared by a polyol solvothermal synthesis process. They were characterised by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectrometry (XPS), dynamic light scattering (DLS) and Fourier transform-infrared (FTIR) spectroscopy. The elemental composition of MnxFe3-xO4 was evaluated by inductively coupled plasma atomic emission spectroscopy. Our results reveal that the oxidation state of the manganese precursor significantly affects the Cr6+ adsorption efficiency of MnxFe3-xO4 NS. The best adsorption capacity for Cr6+ is 16.8 ± 1.6 mg Cr6+/g by the spherical Mn0.22+Fe2.83+O4 nanoparticles at pH 7, which is 1.4 times higher than that of Mn0.8Fe2.2O4 nanoflowers. This was attributed to the relative excess of divalent manganese in Mn0.22+Fe2.83+O4 based on our XPS analysis. The lethal concentration of Cr6+ for S. oneidensis MR-1 was 60 mg L-1 (determined by flow cytometry). The addition of Mn0.22+Fe2.83+O4 nanoparticles to S. oneidensis MR-1 enhanced the bio-reduction of Cr6+ 2.66 times compared to the presence of the bacteria alone. This work provides a cost-effective method for the removal of Cr6+ with a minimum amount of sludge production.
ABSTRACT
Water pollution by heavy metals is one of the most serious worldwide environmental issues. With a focus on copper(II) ions and copper complex removal, in the present study, ultra-small primary CoFe2O4 magnetic nanoparticles (MNPs) coated with octadecylamine (ODA) of adequate magnetization were solvothermally prepared. The surface modification of the initial MNPs was adapted via three different chemical approaches based on amine and/or carboxylate functional groups: (i) the deposition of polyethylimide (PEI), (ii) covalent binding with diethylenetriaminepentaacetic acid (DTPA), and (iii) conjugation with both PEI and DTPA, respectively. FT-IR, TGA, and DLS measurements confirmed that PEI or/and DTPA were successfully functionalized. The percentage of the free amine (-NH2) groups was also estimated. Increased magnetization values were found in case of PEI and DTPA-modified MNPs that stemmed from the adsorbed amine or oxygen ligands. Comparative UV-Vis studies for copper(II) ion removal from aqueous solutions were conducted, and the effect of time on the adsorption capacity was analyzed. The PEI-modified particles exhibited the highest adsorption capacity (164.2 mg/g) for copper(II) ions and followed the pseudo-second-order kinetics, while the polynuclear copper(II) complex Cux(DTPA)y was also able to be immobilized. The nanoadsorbents were quickly isolated from the solution by magnetic separation and regenerated easily by acidic treatment.
ABSTRACT
The use of magnetic nanostructures as theranostic agents is a multiplex task as physiochemical and biochemical properties including excellent magneto-responsive properties, low toxicity, colloidal stability and facile surface engineering capability are all required. Nonetheless, much progress has been made in recent years synthesis of "all-in-one" MNPs remain unambiguously challenging. Towards this direction, in this study is presented a facile incorporation of a soft magnetic phase (MnFe2O4 NPs) with a hard phase (CoFe2O4 NPs) in the presence of the biocompatible polymer sodium dodecyl sulfate (SDS), into spherical and compact bi-magnetic nanoclusters (NCs) with modulated magnetic properties that critically enhance hyperthermic efficiency and MRI contrast effect. Hydrophobic MnFe2O4 and CoFe2O4 NPs coated with oleylamine of the same size (9â¯nm) were used as primary building units for the formation of the bi-magnetic NCs through a microemulsion approach where a set of experiments were conducted to identify the optimal concentration of SDS (19.5â¯mM) for the cluster formation. Additionally, homo-magnetic NCs of MnFe2O4 NPs and CoFe2O4 NPs, respectively were synthesized for comparative studies. The presence of distinct magnetic phases within the bi-magnetic NCs resulting in synergistic behavior, where the soft phase offers moderate coercivity Hc and the hard one high magnetization Ms. Increased specific loss power (SLP) value was obtained for the bi-magnetic system (525â¯W/g) when compared with the homo-magnetic NCs (104â¯W/g for MnNCs and 223â¯W/g for CoNCs) under field conditions of 25â¯kA/m and 765â¯kHz. Relaxivities (r2) of the bi-magnetic NCs were also higher (81.8â¯mM-1â¯s-1) than those of the homo-magnetic NCs (47.4â¯mM-1â¯s-1 for MnNCs and 3.1â¯mM-1â¯s-1 for CoNCs), while the high r2/r1 value renders the system suitable for T2-weighted MRI imaging.
