The selective conversion of CO(2 )into valuable C2+ olefins and higher hydrocarbons offers a cost-effective route to reduce fossil fuel dependence but remains a grand challenge in heterogeneous catalysis due to competing methanation and over-hydrogenation pathways. Here, we elucidate the role of highly electropositive cesium in tuning Fe-based catalysts for CO2 hydrogenation. Systematic variation of Cs/Fe ratios, coupled with XRD, M & ouml;ssbauer spectroscopy, XPS, spatially resolved ELNES, in situ DRIFTS-MS, steady-state kinetics and transient isotopic labelling studies, reveals that Cs-containing species modify the FeOx/FeC(x )ensembles and shift the rate-limiting step in the coupled RWGS-FTS reaction network. At high Cs loadings (Cs/Fe = 0.2), catalysts achieve stable performance with similar to 50% selectivity to C-2=-C-4= olefins and similar to 29% to C5+ hydrocarbons, while suppressing methane formation. Operando studies and temperature programmed reaction show that Cs enriches surface carbides, moderates H-2 activation, and stabilizes CHx intermediates, thereby redirecting hydrocarbon selectivity toward olefins and heavier hydrocarbon. These findings provide molecular-level insights into alkali promotion, highlighting Cs as electronic modulator and geometric spacer of Fe active sites. More broadly, this work establishes alkali-induced modification of FeOx/FeC(x )interfacial environments and RWGS-FTS kinetic balance are controls activity and selectivity in CO2-FTS to high-value chemical and fuels.

In this study, Zn0.5Fe2.5O4 nanopolygons are synthesized using sugarcane juice-mediated facile combustion green route and extensively examined by variety of techniques. PXRD, FTIR, XPS and HRTEM & SAED analysis affirmed formation sugar coated Zn0.5Fe2.5O4 (ZnF) nanoparticles in polygonal (NPs) morphology with a mean particle size of similar to 12 nm in the phase pure fcc structure (space group:Fd3(sic)m). Comprehensive dc-magnetization and Fe-57-Mossbauer analysis revealed that ZnF NPs exhibit superparamagnetism (SPM) at 300 K and soft ferrimagnetic (FiM) character at low temperatures. Vogel-Fulcher and dynamic scaling fits to the exhaustive ac-susceptibility data showed that below 210 K, ZnF NPs enter in the super-spin glass (SSG) state, which is realized from single spin-flip relaxation time (10(-12)s), Mydosh parameter (=0.026) and critical exponent (z nu = 6.7). Moreover, SSG phase is corroborated by the archetypal experimental signatures such as ageing, memory and rejuvenation. Notably, a rare occurrence of Griffith phase (GP) at high temperatures (800 K-900 K) is validated by power law and Arrot plots. Induction heating characteristics of ZnF NPs probed using Infrared thermography yielded Intrinsic Loss Parameter (ILP) ranging 0.32 nHm(2)kg(-1) to 5.53 nHm(2)kg(-1). Theoretical simulations and HRTEM data asserts that only similar to 20 % of NPs contribute to specific absorption rate (SAR). Overall, this meticulous study provides a systematic quantification of magnetic phases such as SSG, the coexistence of SPM and FiM, GP along with a detailed hyperthermia analysis in a greenly synthesized ZnF NPs.

Currently, iron oxide nanoparticles around 25–30 nm in diameter are the standard magnetic tracers used for magnetic particle imaging (MPI) applications. Compared to iron oxide nanoparticles, less research has been performed in creating pure iron nanoparticles for MPI applications. Previous studies have created iron core–iron oxide shell nanoparticles around 15 nm in diameter, but in order to achieve optimal MPI signal similar to iron oxides, larger diameters around 20 nm are needed. However, due to the strong magnetic characteristics of pure iron, synthesizing pure iron nanoparticles above 15 nm in diameter can be challenging due to the high risk of agglomeration. Therefore, an investigation into creating 20-nm-sized iron nanoparticles was performed utilizing potential surfactants that might prevent agglomeration. A thermal decomposition of iron pentacarbonyl was performed with different surfactants including decylamine (DA), dodecylamine (DDA), hexadecylamine (HDA), octadecylamine (ODA), and dioctyldecylamine (DODA) to determine potential differences in size or composition. All surfactants possessed a linear structure and only varied in alkyl-chain length. From the results, it was found that longer alkyl-chain length surfactants assisted in creating larger iron nanoparticle sizes.

The present study comprehensively scrutinizes the complex magnetism and hyperthermia efficiency of greenly synthesized Zn0.25Ca0.25Fe2.5O4 nanoparticles (ZNCF NPs). similar to 23 nm sized ZNCF NPs in single phase fcc-spinel symmetry were successfully produced through sugarcane juice-mediated self-combustion tactics. Biocompatibility examination against BEAS-2B cell lines indicated a safer limit of ZNCF NPs as 1 mg. Exhaustive field (upto +/- 70 kOe) and temperature-dependent (10 K to 300 K) dc-magnetization measurements showed that ZNCF NPs are in the ferrimagnetic (FiM) phase at low temperatures and superparamagnetic (SPM) along with minute magnetically hard FiM component at 300 K. 57Fe-M & ouml;ssbauer analysis validated SPM (43%) and FiM (57%) at 293 K and FiM state at low temperatures. Observed isomer shift revealed that the majority of Fe ions are in a high spin Fe3+ state along with Fe2+ ions in ZNCF NPs. Shifting in the real part of ac-susceptibility data toward the higher temperature side upon increasing frequency and obeying Vogel-Fulcher law affirmed collective freezing of superspins below freezing temperature (Tf = 200 K). Dynamic scaling fit yielded relaxation time of similar to 10-12 s, Mydosh parameter (=0.021) and critical exponent (8.9) ascertaining superspin glass (SSG) state in ZNCF NPs below glass temperature (Tg = 220 K). Furthermore, SSG phase at low temperatures is approved by archetypal experimental signatures like ageing, memory and rejuvenation. The induction heating characteristics of ZNCF NPs probed via infrared thermography yielded intrinsic loss parameter in the 0.26 nHm2 kg-1-5.10 nHm2 kg-1 range. Linear response theory provided non-zero power dissipation for ZNCF (suspension in de-ionized water) functioning range of 6-8 nm with an optimum particle size of similar to 7 nm. A prudent analysis asserted that only 18% of NPs contribute to a non-zero SAR value. Overall, this research is an exhaustive investigation of the complex magnetism and hyperthermia efficiency suitable for mild hyperthermia applications.

Ionizing radiation has become widely used in medicine, with application in diagnostic techniques, such as computed tomography (CT) and radiation therapy (RT), where X-rays are used to diagnose and treat tumors. The X-rays used in CT and, in particular, in RT can have harmful side effects; hence, an accurate determination of the delivered radiation dose is of utmost importance to minimize any damage to healthy tissues. For this, medical specialists mostly rely on theoretical predictions of the delivered dose or external measurements of the dose. To extend the practical use of ionizing radiation-based medical techniques, such as magnetic resonance imaging (MRI)-guided RT, a more precise measurement of the internal radiation dose internally is required. In this work, a novel approach is presented to measure dose in liquids for potential future in vivo applications. The strategy relies on MRI contrast agents (CAs) that provide a dose-sensitive signal. The demonstrated materials are (citrate-capped) CaF2 nanoparticles (NPs) doped with Eu3+ or Fe2+/Fe3+ ions. Free electrons generated by ionizing radiation allow the reduction of Eu3+, which produces a very small contrast in MRI, to Eu2+, which induces a strong contrast. Oxidative species generated by high-energy X-rays can be measured indirectly using Fe2+ because it oxidizes to Fe3+, increasing the contrast in MRI. Notably, in the results, a strong increase in the proton relaxation rates is observed for the Eu3+-doped NPs at 40 kV. At 6 MV, a significant increase in proton relaxation rates is observed using CaF2 NPs doped with Fe2+/Fe3+ after irradiation. The presented concept shows great promise for use in the clinic to measure in vivo local ionizing radiation dose, as these CAs can be intravenously injected in a saline solution.

Magnetic nanostructured materials (MNMs) have gained prominence in materials technology developments owing to their potential biomedical applications for hyperthermia cancer treatment, and transplant organ cryopreservation. Herein, we report the facile and cost-effective synthesis of Fe-based composite MNMs, comprising both Fe@Fe2O3 and Fe3C@C core-shell nanoparticles (NPs), via Laser Ablation Synthesis in Solution (LASiS) using Fe targets ablated under acetone and toluene. Detailed materials characterizations using electron microscopy-based imaging, diffraction studies, and spectroscopic analyses - including Raman and Mossbauer spectroscopy - relate the structure-composition properties for different Fe-oxide/carbide phases in the aforesaid MNMs to their respective magnetic responses. Specifically, we confirm the presence of ultra-small (2-10 nm) amorphous Fe-oxide NPs, as well as Fe@Fe2O3 core-shell NPs (20-40 nm) in the samples synthesized by ablating Fe under acetone. In contrast, samples synthesized under toluene indicate a higher concentration of Fe3C@C core-shell NPs (20-40 nm) with a relatively low concentration of Fe2O3 NPs (2-10 nm). Furthermore, the crystallinity of the metallic phases and carbonaceous shell coatings are systematically increased by carrying out LASiS under heated toluene (up to -95 degrees C). Mossbauer spectroscopy results indicate that the elevation in toluene temperature leads to an increase in the concentrations of Fe3C@C NPs from -40 % to -53 % (at.).

Iron based nanoparticles have shown promise in biomedical applications by possessing diagnostic and therapeutic capabilities. Currently, superparamagnetic iron oxide nanoparticles (SPIONs) are the standard magnetic materials used for magnetic based imaging and hyperthermia therapeutics due to their good magnetic properties, biocompatibility, and stability. However, further improvement of iron-based nanoparticles for such applications can be achieved by creating nanoparticles that possess a pure iron core. Therefore, this study investigates a one-pot synthesis of superparamagnetic iron core–shell nanoparticles using a thermal decomposition of iron pentacarbonyl. Reaction time and surfactant quantities were modified to investigate possible size, shape, and dispersion variations. Characterizations included transmission electron microscopy, x-ray diffraction, Mössbauer spectroscopy, vibrating sample magnetometry, zeta potential, and cytotoxicity studies. From this method, core–shell, monodispersed nanoparticles averaging 14 nm in size were produced and displayed good colloidal stability and high magnetic saturation up to 130 emu/g. Iron nanoparticles were coated with 1,2- distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy- (polyethylene glycol)-2000] (ammonium salt) (DSPE-mPEG) polymer to increase biocompatibility and showed low cytotoxicity. The nanoparticles reported display high potential for magnetic imaging and magnetic hyperthermia applications.

The influence of trace element concentrations on luminescence in natural topaz is not adequately described in the literature.Investigating the luminescence and geochemical characteristics of topaz could lead to a better understanding of peraluminous, Prich, and Ca-poor igneous rocks, which are associated with rare metal ore deposits.To evaluate the intra-crystal relationship of trace element concentration, color, and luminescence, we present ultra-violet (λ ~ 225 nm) luminescence assisted LA-ICPMS, FTIR, and Mössbauer spectroscopy results for 108 alluvial topaz from Guyana, Brazil, Zimbabwe, and Mexico.FTIR spectroscopy suggests a substitution of F by OH of ~42%, likely corresponding with pegmatite to hydrothermal paragenesis.Mössbauer spectroscopy of colorless, orange, and blue topaz indicates no detectable Fe 2+ whereas green topaz records Fe 3+ /Fe 2+ ~ 2.23.Our results indicate green topaz may be influenced by the relative contributions of Fe 3+ and Fe 2+ and form in a more reducing environment.We also demonstrate trends amongst color, growth zones, and luminescence related to the concentrations of Fe, Cr, Mn, Li, V, P, Ti, Ta, W, Nb (±1σ).Orange topaz has the highest concentration of Fe (3430±64.3ppm) followed by sherry (244±33 ppm), green (137.9±49.3ppm), and blue (39.6±64.1 ppm).Euhedral and luminescent red, teal, and blue zones reflect different growth events.Red luminescent zones occur as a thin rim along blue and/or teal luminescent cores.Red luminescence zones have high Fe (1735.4±124.5 ppm), Cr (99.6±96 ppm), V (15.9±15 ppm), and low P (148.2±68ppm), Li (1.5±0.7 ppm), and Ti (10.4±2.4 ppm).In contrast blue and teal luminescence zones have lower Fe (74.6±84.2ppm), Cr (2.8±7.3 ppm), V (0.4±0.4 ppm), and higher P (326.7±239.3ppm), Li (13±23.4ppm), and Ti (61.1±38.4ppm).Red luminescent zones have < 0.2 ppm Ta, W, and Nb, but blue to teal luminescent zones have higher Ta (0.7±0.9 ppm), W (0.7±0.9 ppm), and Nb (1.2±1.5 ppm).Relatively high P and Li cores and low Fe, Cr, V, rims suggest strongly differentiated host rocks altered by hydrothermal mineralization.Furthermore, enrichment of Ta, W, and Nb corresponding with alluvial topaz luminescence color may be a quick indicator of rare metal mineralization in nearby rocks.

The development of inexpensive radiation-resistant glass is important for potential applications in displays, optics, and nuclear or space environments. This study considers the γ-ray and X-ray resistance of glasses relevant to low-cost float glass (i.e., SiO2–Na2O–CaO–MgO), modified with various concentrations (0 – 10 mol%) of Sb2O3. Various doses (0, 0.2, 2.0, and 5.0 MGy) of γ-rays from the decay of 60Co nuclei, and X-rays generated by an X-ray fluorescence (XRF) spectrometer, have been applied to this series of Sb2O3-modified float-type glasses to study their resistance to radiation-induced damage. Irradiation leads to the formation of various defect centres (HC2, HC1, TE, E', and E− types). These radiation-induced defects cause photo-darkening of the glass, which reduces its visible-wavelength optical transparency. The addition of Sb2O3 to these glasses led to reductions in the formation of radiation-induced defect-centres, combined with forbidden bandgap narrowing which led to non-linear changes in visible-wavelength absorption as a function of Sb2O3 content such that the most transparent irradiated glasses were advantageously obtained at low (0.5 mol%) Sb2O3 content. The mechanisms of defect-formation involve the creation of Sb4+-ions which assists in mitigating the effects of irradiation on the visible-wavelength transparency of the glass. The 0.5 mol% of Sb2O3-modified float glass provided a maximized concentration of Sb4+-ions upon γ-ray irradiation. Combined with the smallest changes in the UV band gap narrowing, it enabled this glass to retain the highest visible-wavelength transparency at all doses of ionizing radiation studied (0.2, 2 and 5 MGy). This work confirms the substantially enhanced radiation resistance of Sb2O3-modified float-type glasses compared to standard float glass, which could potentially be further developed towards commercialization, for example as a low-cost solution for radiation resistant applications.

Spherical, mono-disperse, non-interacting iron oxide (Fe3O4) nanoparticles, synthesized by high-temperature hydrolysis of chelated iron alkoxide complexes, have been studied by Mo center dot ssbauer spectroscopy. The critical diameter for room temperature superparamagnetism, an important parameter for high frequency biomedical (MRI) and IT applications, was about 11 nm. Particles of diameter 11.9 nm and greater are ferrimagetic and showed magnetic splitting. Particles of diameter 10.6 nm and smaller are superparamagnetic and gave a nonmagnetic spectrum at room temperature. The lines narrow as the particle size decreases and the spin relaxation rate increases. For the smallest particles (8.6 nm or less) the room temperature spectra could be resolved into two partially overlapping lines, one from the A-sites and one from the B-sites, the latter being broadened by the nuclear quadrupole interaction. Similar spectra have been previously reported for bulk Fe3O4 above the Curie point. The isomer shifts showed anomalies possibly arising from magnetostrictive atomic displacements. On applying a magnetic field of 20 kG, hyperfine splitting was observed, confirming that the particles are singledomain with large magnetic moments of the order of 104 mu B. The in-field spectrum was similar to that of bulk crystals above the Verwey temperature with Fe3+on the A-sites and Fe2.5+ on the B-sites, characteristic of the inverse cubic spinel structure. The lines narrowed as the temperature was decreased until magnetic splitting was observed at temperatures below the blocking temperature TB, where the magnetic fluctuations are blocked. The transition to the magnetic state is smooth, confirming that the particles are mono-disperse. At the lowest temperature (6 K) the spectra resemble those of bulk Fe3O4 with Fe3+on the A-sites and both Fe2+ and Fe3+ on the Bsites corresponding to the local monoclinic distortion, indicating that the nanoparticles have undergone a Verwey transition. The values of TB found are lower than those reported by most other researchers, suggesting that magnetic interactions between our particles are small. The non-stoichiometry parameter, x, defined by the formula Fe3-xO4, was estimated from the relative amounts of Fe3+/ Fe2+ and from isomer shifts to be less than 0.1 in the different samples.

Mössbauer spectra of Feridex, an MRI enhancement agent, show that it contains superparamagnetic γ-Fe2O3 nanoparticles. From spectra in magnetic fields applied at room temperature the magnetic moment of the particles was measured to be 11,250 μB, from which the diameters of the single-domain particles are estimated to be about 8 nm. This is smaller than the hydrodynamic particle size of 30 nm which includes a protective coating of dextran. The particles are monodisperse, as shown by the continuous change from a broad superparamagnetic line to a magnetic 6-line pattern as the temperature is lowered below the blocking temperature TB of about 90 K. The magnetic moments and blocking temperature are consistent with those of γ-Fe2O3 samples of known sizes.

Magnetic nanoparticles (MNPs) have many uses for biomedical applications including drug delivery, magnetic resonance imaging (MRI) contrast agents, theranostics and hyperthermia. MNPs photo-thermally heated by laser light could be used to treat the typically difficult to access tumors such as glioblastomas. Due to their high magnetic saturation, monometallic iron nanoparticles would have an edge over iron oxide nanoparticles currently being investigated for hyperthermia. The goal of this study was to synthesize spherical iron nanoparticles less than 10 nm in diameter by thermal decomposition. The ability of various biocompatible coatings to protect the metallic iron nanoparticles from oxidation was investigated. Coatings studied included Brij, polyethylene glycol and iron oxide. Transmission electron microscopy and Mössbauer spectroscopy were utilized to characterize the coated and uncoated iron nanoparticles’ size and oxidation state to evaluate the effectiveness of the coatings and the procedures in which the coatings were applied. A ferrite shell was found to provide the best stabilization; however, its longer synthesis time increased particle size distribution. Polymer coatings provided biocompatibility but did not prevent oxidation.

Float glass-type SiO2-Na2O-CaO glasses with 0 - 10 mol% Sb2O3 were melted and their compositional, structural, thermal and optical properties characterised. All glasses were X-ray amorphous and increasing Sb2O3 content progressively decreased glass transition temperature (T-g) and dilatometric softening point (T-d), despite increases in Al2O3 content from greater crucible corrosion. Sb-121 Mossbauer spectroscopy confirmed that Sb was predominantly incorporated as Sb3+ (Sb3+/Sigma Sb similar to 0.9) and Raman spectroscopy showed that Sb substantially decreased average (Si, Al)-O Q(n) speciation. Both techniques confirmed that Sb3+ ions were incorporated in trigonal pyramidal [:SbO3] polyhedra. XRF and Raman spectroscopies confirmed that SO3 content decreased with increasing Sb2O3 content. TGA analysis showed, as a linear function of Sb2O3 content, mass gain commencing at 700 degrees C, reaching a maximum at 1175 degrees C, then mass loss above 1175 degrees C, consistent with oxidation (Sb3+ -> Sb5+) then reduction (Sb5+ -> Sb3+). The TGA samples were shown to have attained or approached Sb redox equilibrium during measurement. Optical absorption spectroscopy (UV-Vis-nIR) showed red-shifts of the UV absorption edge with increasing Sb2O3 content, consistent with increasing intensity of far-UV absorption bands from Sb3+ and Sb5+ s -> p transitions. UV-Vis-nIR fluorescence spectroscopy evidenced a broad luminescence band centred at similar to 25,000 cm(-1), attributed to the P-3(1)-> S-1(0) transition of Sb3+, which is Stokes shifted by similar to 15,000 cm(-1) from the S-1(0)-> P-3(1) absorption at similar to 40,000 cm(-1). The most intense emission occurred at 0.5 mol% Sb2O3, with concentration quenching reducing luminescence intensities at higher Sb2O3 contents. Additions of Sb2O3 to float-type soda-lime-silica glasses could thus enable lower melting energies and/or new solar energy applications.

A method is presented for synthesizing core-shell nanoparticles with a magnetic core and a porous shell suitable for drug delivery and other medical applications. The core contains multiple γ-Fe2O3 nanoparticles (∼15 nm) enclosed in a SiO2 (∼100-200 nm) matrix using either methyl (denoted TMOS-γ-Fe2O3) or ethyl (TEOS-γ-Fe2O3) template groups. Low-temperature Mössbauer spectroscopy showed that the magnetic nanoparticles have the maghemite structure, γ-Fe2O3, with all the vacancies in the octahedral sites. Saturation magnetization measurements revealed that the density of γ-Fe2O3 was greater in the TMOS-γ-Fe2O3 nanoparticles than TEOS-γ-Fe2O3 nanoparticles, presumably because of the smaller methyl group. Magnetization measurements showed that the blocking temperature is around room temperature for the TMOS-γ-Fe2O3 and around 250 K for the TEOS-γ-Fe2O3. Three dimensional topography analysis shows clearly that the magnetic nanoparticles are not only at the surface but have penetrated deep in the silica to form the core-shell structure.

A route for synthesizing monodisperse magnetic nanocrystallites of maghemite, [Formula: see text]-Fe2O3, with various sizes has been revisited. A systematic investigation of three [Formula: see text]-Fe2O3 nanocrystalline samples by different techniques has been performed to characterize their size-dependent magnetic properties. Zero-field-cooled and field-cooled magnetization measurements reveal that the superparamagnetic blocking temperatures are around 230 K, 170 K, and 50 K for the 15.0 nm, 11.8 nm, and 6.1 nm nanocrystallites, respectively. Low-temperature Mössbauer spectra show that all three nanocrystallites have the maghemite structure with all the vacancies in the B-sites. Furthermore, detailed analysis shows that there are more vacancies on the B-sites for the 6.1 nm nanocrystallites compared to 0.33 for the bulk maghemite.

INTRODUCTION:Cognitive impairment is a common complication of Parkinson's disease (PD) and identifying risk factors for progression to Parkinson's disease dementia (PDD) is important. However, little research has been done comparing the utility of commonly used cognitive screening tests in predicting cognitive progression in PD. METHODS:We retrospectively reviewed data from patients with PD enrolled in the Pacific Udall Center who had baseline and longitudinal neuropsychological and global cognitive screening tests. The diagnostic accuracies of 3 common screening tests were compared: Montreal Cognitive Assessment (MoCA), Mattis Dementia Rating Scale (DRS-2), and Mini Mental Status Examination (MMSE). Cognitive diagnoses of PD with mild cognitive impairment (PD-MCI) and PDD were based on full neuropsychological testing and established Movement Disorder Society criteria. Logistic regression and Cox proportional hazards regression models were used to examine predictors of cognitive decline. RESULTS:Four hundred seventy patients for whom scores on all 3 screening tests were available from the same assessment were included in a cross-sectional analysis. The MoCA demonstrated the best overall diagnostic accuracy for PD-MCI (AUC= 0.79, sensitivity= 76.4%) and for PDD (AUC= 0.89, sensitivity= 81.0%) compared to the DRS-2 and MMSE. A longitudinal analysis was performed on the subset of patients (316/470; 67.2%) who were nondemented at baseline and had undergone two or more assessments. After controlling for covariates, the MoCA was the only test associated with progression to PDD (OR= 1.27 95% CI 1.1 - 1.5, p=0.001) and faster time to dementia (HR = 1.3, 95% CI 1.1 - 1.4, p<0.0001). CONCLUSIONS:This study provides additional support for the use of the MoCA as a primary screening tool for cognitive impairment in PD and is the first to show that the MoCA is a predictor of conversion to PDD.

Magnesium- and cobalt- substituted FeSb2O4, of composition Fe1−xMgxSb2O4 (x = 0.25, 0.50, 0.75) and Fe0.25Co0.75Sb2O4 have been examined by 57Fe Mössbauer spectroscopy. The complex spectra recorded from the magnetically ordered materials are interpreted in terms of models in which the dominant magnetic interactions occur along the rutile-related chains of FeO6 octahedra in the magnetic structure of FeSb2O4. In materials of the type Fe1−xMgxSb2O4, the diamagnetic Mg2+ ions have no magnetic moment and behave as non-magnetic blocks which disrupt the magnetic interactions in the chains along the c-axis forming segments of iron-containing chains separated by Mg2+ ions. In Fe0.25Co0.75Sb2O4 the spectra are composed of components from different configurations of neighbouring Fe2+ and Co2+ ions.

A systematic investigation of magnetic nanoparticles and the formation of a core-shell structure, consisting of multiple maghemite (gamma-Fe2O3) nanoparticles as the core and silica as the shell, has been performed using various techniques. High-resolution transmission electron microscopy clearly shows isolated maghemite nanoparticles with an average diameter of 13 nm and the formation of a core-shell structure. Low temperature Mossbauer spectroscopy reveals the presence of pure maghemite nanoparticles with all vacancies at the B-sites. Isothermal magnetization and zero-field-cooled and field-cooled measurements are used for investigating the magnetic properties of the nanoparticles. The magnetization results are in good accordance with the contents of the magnetic core and the non-magnetic shell. The multiple-core gamma-Fe2O3 nanoparticles show similar behavior to isolated particles of the same size. (C) 2017 Elsevier B.V. All rights reserved.