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Origin of reduced magnetization and domain formation in small magnetite nanoparticles.

ABSTRACT: The structural, chemical, and magnetic properties of magnetite nanoparticles are compared. Aberration corrected scanning transmission electron microscopy reveals the prevalence of antiphase boundaries in nanoparticles that have significantly reduced magnetization, relative to the bulk. Atomistic magnetic modelling of nanoparticles with and without these defects reveals the origin of the reduced moment. Strong antiferromagnetic interactions across antiphase boundaries support multiple magnetic domains even in particles as small as 12-14 nm.

SUBMITTER: Nedelkoski Z

PROVIDER: S-EPMC5385549 | biostudies-literature | 2017 Apr

REPOSITORIES: biostudies-literature

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Origin of reduced magnetization and domain formation in small magnetite nanoparticles.

Nedelkoski Zlatko Z Kepaptsoglou Demie D Lari Leonardo L Wen Tianlong T Booth Ryan A RA Oberdick Samuel D SD Galindo Pedro L PL Ramasse Quentin M QM Evans Richard F L RF Majetich Sara S Lazarov Vlado K VK

Scientific reports 20170410

The structural, chemical, and magnetic properties of magnetite nanoparticles are compared. Aberration corrected scanning transmission electron microscopy reveals the prevalence of antiphase boundaries in nanoparticles that have significantly reduced magnetization, relative to the bulk. Atomistic magnetic modelling of nanoparticles with and without these defects reveals the origin of the reduced moment. Strong antiferromagnetic interactions across antiphase boundaries support multiple magnetic do ...[more]

PMID: 28393876

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Project description:Heterostructures of magnetite (Fe3O4) nanoparticles and reduced graphene oxide (RGO) sheets are very common composite materials for different applications such as catalysis, energy storage, and biomedicine. Developing methods for the facile control of the size and shape of both freestanding Fe3O4 nanoparticles and those anchored onto RGO sheets is in demand. Herein, we report on the rapid and facile microwave synthesis (MWS) of Fe3O4 nanoparticles and Fe3O4/RGO with various sizes and shapes using the oleylamine (OAm)/oleic acid (OAc) ligand pair. The solvothermal synthesis using microwave irradiation (MWI) resulted in the concurrent conversion of graphene oxide (GO) into RGO and the in-situ formation of various-shaped Fe3O4 on RGO sheets. Freestanding Fe3O4 nanoparticles of various shapes were prepared using MWS for comparison. The morphological, structural, and surface properties of the samples were studied using different characterization techniques. The magnetization properties of the prepared samples were determined using a vibrating sample magnetometer. Various-shaped standalone and RGO-supported Fe3O4 nanoparticles including nanospheres, nanocubes, and nanotriangles were synthesized via MWI at 1000 W for 20 min by changing the ratios of the iron precursor and the OAm/OAc ligand pair. Interestingly, the MWI using OAm/OAc ligand pair of a molar ratio of 3:4 resulted in the in-situ formation of large hexagonal Fe3O4/RGO. The X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) results confirm the crystallinity and spinel structure of the prepared Fe3O4 samples and prove the concurrent conversion of GO into RGO with assemblies of Fe3O4 nanoparticles. The magnetization measurements further emphasized the role of size and shape in affecting the magnetic properties of Fe3O4 and Fe3O4/RGO heterostructures. The results identify the qualities of the prepared samples and prove the MWS as a facile one-pot method for the preparation of Fe3O4 and Fe3O4/RGO heterostructures.

Project description:Synthetic dyes are predominantly emitted into the eco-environment resulting, in harmful effects on the environment and human. This study presents a new perspective on the mesoporous silica (SBA-16) and reduced graphene oxide (rGO) obtained from rice husk ash as substrates for Fe3O4 nanoparticles (NPs) to investigate their morphological and Fenton catalytic characteristics towards degradation of synthetic acid blue 40 dye (AB40). The adsorption and Fenton catalytic properties of AB40 dye by the prepared Fe3O4, Fe3O4/SBA-16 and Fe3O4/rGO catalysts were examined. The successful synthesis of such catalysts was affirmed by the results obtained from FE-SEM, EDX, TEM, FTIR, XRD and nitrogen adsorption measurements. The adsorption of AB40 dye followed the Langmuir model, with maximum adsorption capacities of 169.2, 21.1 and 16.6 mg/g for Fe3O4, for Fe3O4/SBA-16 and Fe3O4/rGO, respectively. This result was explained based on their specific surface areas. The decolorization efficiency was estimated through several factors, including initial dye concentration, pH and H2O2 concentration. The results disclosed that a catalyst dose = 1 g/L, initial dye concentration = 50 mg/L, pH = 3 and [H2O2] = 15 mmol/L are the optimum conditions for full decolorization of AB40 within 60 min at 35 °C. The prepared Fe3O4 NPs exhibited a superior Fenton activity at 25 °C and pH 3. However, both composites increased Fenton performance above 25 °C, indicating that SBA-16 and rGO substrates can enhance the stability of Fe2+ to generate a higher amount of hydroxyl radicals. Regeneration results disclosed that the obtained Fenton-like catalysts revealed notably high catalytic efficiency (> 95%) and stability, with minimal decrease in activity observed after running four cycles of AB40 dye degradation at pH 3 and 35 °C. Thus, this study demonstrated that both SBA-16 and rGO substrates obtained from rice husk ash improved the reusability and stability of Fe3O4 catalysts in wastewater treatment using heterogeneous Fenton reactions.

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Origin of reduced magnetization and domain formation in small magnetite nanoparticles.

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Origin of reduced magnetization and domain formation in small magnetite nanoparticles.

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