Jeotikanta Mohapatra

Mesoporous iron oxide nanowires: synthesis, magnetic and photocatalytic properties

A surfactant- and template-free approach is described for the synthesis of mesoporous α-Fe2O3, Fe3O4 and α-Fe nanowires (NWs). In this approach, α-FeOOH NWs (length 550 nm and diameter 30 nm) were first prepared by hydrolysis of FeCl3. On subsequent thermal treatment in a fluidized bed reactor in the presence of a forming gas (Ar 93% + H2 7%), α-FeOOH transformed to mesoporous NWs of ɑ-Fe2O3, Fe3O4 and ɑ-Fe by controlling the process parameters such as reaction time and temperature. The obtained NWs of α-Fe2O3, Fe3O4 and α-Fe were ferromagnetic at room temperature with a coercive field (Hc) of 412, 583 and 628 Oe respectively. The aligned NWs showed 1.6 to 2 times-enhanced remanence in the parallel direction relative to the perpendicular direction due to magnetic anisotropy. These mesoporous magnetic NWs with a high specific surface area (82 m2 g−1 for α-Fe2O3 NWs) were used in photocatalysis due to the high adsorptivity of three probe dye molecules. The as-prepared α-Fe2O3 NWs exhibited only modest photocatalytic activity; however, the catalytic activity could be further enhanced by decorating the mesoporous ɑ-Fe2O3 NWs with 10 nm sized ZnO nanoparticles. The developed ɑ-Fe2O3/ZnO nanowire nanohybrids could eliminate 100% of the probe dyes: methylene blue, Rhodamine B and methyl orange within 90 min irradiation with solar light, underlining the high photocatalytic degradation efficiency of the nanohybrid. The nanowire nanohybrids could be easily recovered by applying an external magnetic field and reused for at least 4 times without significant loss of their photocatalytic activity.

Magnetic and hyperthermia properties of CoxFe3-xO4 nanoparticles synthesized via cation exchange

We demonstrate magnetic and hyperthermia properties of CoxFe3-xO4 (x = 0, 0.1, 0.3 and 0.5) nanoparticles synthesized via a simple cation exchange reaction of ∼12 nm Fe3O4 nanoparticles. The substitution of Fe cations with Co2+ ions leads to enhanced magnetocrystalline anisotropy and coercivity of the pristine superparamagnetic Fe3O4 nanoparticles. Hyperthermia measurement shows that by controlling the Co content (x = 0 to 0.5) in CoxFe3-xO4 nanoparticles, their specific absorption rate (SAR) can be greatly improved from 132 to 534 W/g. The strong enhancement in SAR value is attributed to the increased anisotropy and coercivity. Moreover, with the increase of ac magnetic field from 184 to 491 Oe, the SAR values of Fe3O4 and Co0.5Fe2.5O4 nanoparticles increase from 81 to 132 W/g and 220 to 534 W/g, respectively.

Cleaning of magnetic nanoparticle surfaces via cold plasmas treatments

We report surface cleaning of magnetic nanoparticles (SmCo5 nanochips and CoFe2O4 nanoparticles) by using cold plasma. SmCo5 nanochips and CoFe2O4 nanoparticles, coated with surfactants (oleic acid and oleylamine, respectively) on their surfaces, were treated in cold plasmas generated in argon, hydrogen or oxygen atmospheres. The plasmas were generated using a capacitively coupled pulsed radio frequency discharge. Surface cleaning of nanoparticles was monitored by measurement of the reduction of surface carbon content as functions of plasma processing parameters and treatment times. EDX and XPS analyses of the nanoparticles, obtained after the plasma treatment, revealed significant reduction of carbon content was achieved via plasma treatment. The SmCo5 nanochips and CoFe2O4 nanoparticles treated in an argon plasma revealed reduction of atomic carbon content by more than 54 and 40 in atomic percentage, compared with the untreated nanoparticles while the morphology, crystal structures and magnetic properti...

Large T 1 contrast enhancement using superparamagnetic nanoparticles in ultra-low field MRI

Superparamagnetic iron oxide nanoparticles (SPIONs) are widely investigated and utilized as magnetic resonance imaging (MRI) contrast and therapy agents due to their large magnetic moments. Local field inhomogeneities caused by these high magnetic moments are used to generate T2 contrast in clinical high-field MRI, resulting in signal loss (darker contrast). Here we present strong T1 contrast enhancement (brighter contrast) from SPIONs (diameters from 11u2009nm to 22u2009nm) as observed in the ultra-low field (ULF) MRI at 0.13 mT. We have achieved a high longitudinal relaxivity for 18u2009nm SPION solutions, r1u2009=u2009615u2009s−1 mM−1, which is two orders of magnitude larger than typical commercial Gd-based T1 contrast agents operating at high fields (1.5xa0T and 3xa0T). The significantly enhanced r1 value at ultra-low fields is attributed to the coupling of proton spins with SPION magnetic fluctuations (Brownian and Néel) associated with a low frequency peak in the imaginary part of AC susceptibility (χ”). SPION-based T1-weighted ULF MRI has the advantages of enhanced signal, shorter imaging times, and iron-oxide-based nontoxic biocompatible agents. This approach shows promise to become a functional imaging technique, similar to PET, where low spatial resolution is compensated for by important functional information.

Author Correction: Large T 1 contrast enhancement using superparamagnetic nanoparticles in ultra-low field MRI

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper.

Magnetic properties of nickel carbide nanoparticles with enhanced coercivity

Rhombohedral nickel carbide (Ni3Cx, x=0.7, 1.2 and 1.5) nanoparticles (∼ 110 nm) with enhanced magnetic coercivity (HC up to 1.3 kOe) at temperature below the spin-glass freezing (Tf) have been demonstrated. The presence of spin-glass state, which is seen at ∼17 K, is evident by the field dependence of the freezing temperature following the de Almeida–Thouless (AT) relationship and frequency dependence of Tf. Moreover, the spin-glass state is irreversible to the sweeping applied field and results in high HC at 10 K. With increases of the carbon content, we have found a gradual increasing trend in the saturation magnetization (MS: 6.6 to 9.2 emu/g) and coercivity (350 Oe to 1.3kOe) at 10 K. This is attributed to the increase of spin-glass contribution and the weak ferromagnetic phase.

Exchange Coupling in Soft Magnetic Nanostructures and its Direct Effect on their Theranostic Properties

Exchange coupling between hard and soft magnetic materials at the nanoscale exhibits novel or improved physical properties for energy and data storage applications. Recently, exchange coupling has also been explored in core/shell magnetic nanostructures (MNS) composed of hard and soft magnetic spinel ferrites, but applications have been limited in biomedicine due to the presence of toxic cobalt based ferrites as hard magnetic component. We report core/shell MNS where both core and shell components are soft magnetic ferrites (Fe3O4, MnFe2O4, and Zn0.2Mn0.8Fe2O4) and show that exchange coupling still exists due to the difference in their anisotropy. The physical properties (saturation magnetization, susceptibility, anisotropy, r2 relaxivity, and specific absorption rate) of core/shell MNS are compared with the same size single phase counterparts which excludes any size dependent effect and gives the direct effect of exchange coupling. After optimization of core and shell components and their proportions, we have shown that a core/shell MNS shows significantly higher contrast enhancement and thermal activation properties than their single phase counterparts due to exchange coupling between core and shell ferrites. Our finding provides a novel way to improve theranostic properties of spinel ferrite based MNS while maintaining their biocompatibility.

Enhanced coercivity in Co-doped α-Fe2O3 cubic nanocrystal assemblies prepared via a magnetic field-assisted hydrothermal synthesis

Ferromagnetic Co-doped α-Fe2O3 cubic shaped nanocrystal assemblies (NAs) with a high coercivity of 5.5 kOe have been synthesized via a magnetic field (2 kOe) assisted hydrothermal process. The X-ray diffraction pattern and Raman spectra of α-Fe2O3 and Co-doped α-Fe2O3 NAs confirms the formation of single-phase α-Fe2O3 with a rhombohedral crystal structure. Electron microscopy analysis depict that the Co-doped α-Fe2O3 NAs synthesized under the influence of the magnetic field are consist of aggregated nanocrystals (∼30 nm) and of average assembly size 2 μm. In contrast to the NAs synthesized with no magnetic field, the average NAs size and coercivity of the Co-doped α-Fe2O3 NAs prepared with magnetic field is increased by 1 μm and 1.4 kOe, respectively. The enhanced coercivity could be related to the well-known spin–orbit coupling strength of Co2+ cations and the redistribution of the cations. The size increment indicates that the small ferromagnetic nanocrystals assemble into cubic NAs with increased size ...