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In the present study, nanocomposites having hierarchical nanoflowers (HNFs) -like morphology were synthesized by ultra-sonication approach. HNFs were ternary composite of MgFe2O4 and bentonite with boron-, phosphorous- co-doped graphene oxide (BPGO). The HNFs were fully characterized using different analytical tools viz. X-ray photoelectron spectroscopy, scanning electron microscopy, energy dispersion spectroscopy, transmission electron microscopy, X-ray diffraction, vibrating sample magnetometry and Mössbauer analysis. Transmission electron micrographs showed that chiffon-like BPGO nanosheets were wrapped on the MgFe2O4-bentonite surface, resulting in a porous flower-like morphology. The red-shift in XPS binding energies of HNFs as compared to MgFe2O4-bentoniteand BPGO revealed the presence of strong interactions between the two materials. Box–Behnken statistical methodology was employed to optimize adsorptive and photocatalytic parameters using Pb(II) and malathion as model pollutants, respectively. HNFs exhibited excellent adsorption ability for Pb(II) ions, with the Langmuir adsorption capacity of 654 mg g−1 at optimized pH 6.0 and 96% photocatalytic degradation of malathion at pH 9.0 as compared to MgFe2O4-bentonite and BPGO. Results obtained in this study clearly indicate that HNFs are promising nanocomposite for the removal of inorganic and organic contaminants from the aqueous solutions.

Thick freestanding iron-doped semi-insulating GaN layers were grown by Hydride Vapor Phase Epitaxy on GaN/sapphire templates. Iron doping was achieved by using Fe57-enriched Fe2O3 reduced to elemental Fe in-situ avoiding uptake of C from organometallic sources. The morphology and crystalline quality of the films show no evidence of degradation upon iron doping. Mossbauer and spin resonance experiments demonstrate that the Fe-impurity is in the isolated Fe3+ paramagnetic state and no Fe-precipitates are formed at the highest doping levels. Low temperature photoluminescence studies are consistent with full compensation of the shallow pervasive Si and O donors.

Nanoparticles of iron oxide play an important role on the field of nanotechnology and nanoscience presenting tremendous potential for various applications. Oleic acid has been shown to be a promising coating material, allowing to obtain monodisperse, uniform and stable nanoparticles. However, for certain applications which utilize the encapsulation of magnetic nanoparticles into polymer matrices it becomes necessary to use coating materials which exhibit functional groups in their structure capable of avoiding leaching problems. To this end, the present study aimed to develop magnetite nanoparticles coated with chemically modified oleic acid. The reactive functional group present in the fatty acid molecule can promote polymerization between the monomer species and the coating material with high encapsulation efficiency. The different steps of the reactions to obtain acrylated oleic acid were evaluated by Fourier transform infrared (FTIR) spectroscopy and 1H nuclear magnetic resonance spectroscopy. The coated nanoparticles were characterized by FTIR, thermogravimetric analysis, X-ray diffraction, transmission electron microscopy, Mossbauer spectroscopy, Raman spectroscopy and magnetization measurements. The coated nanoparticles showed high dispersibility with a uniform average size of 9.5 nm, saturation magnetization of 61.2 emu/g and superparamagnetic behavior, which make it a very promising for the formation of nanocomposites.

The present study reports on aluminum substituted cobalt ferrite (CoAlxFe2-xO4) nanoparticles (0.00 ≤ x ≤ 2.00) synthesized by combustion reaction method and investigated by transmission electron microscopy, magnetometry, x-ray diffraction, Raman, UV-Vis, and Mossbauer spectroscopies. Within the detection limit of the used techniques, single-phased materials are identified in the whole range of composition (0.00 ≤ x ≤ 2.00). Furthermore, it is observed that the lattice parameter (a) follows the Vegard’s Law, suggesting that the nominal Al3+-ion content (x) effectively replace the Fe3+-ion in the spinel structure. It is observed that the intensity of the diffraction peaks changes as the aluminum content distribution varies. With the help of the Rietveld refinement method and the Mossbauer spectroscopy, this behavior allows one to calculate the cation distribution in A- and B-sites of the spinel structure. The assessed cationic occupation is in excellent agreement with the magnetic measurements data, validating the method herein used to determine the cation’s distribution. Additionally, it is verified that in the transition between inverse to normal spinel, a nearly homogenous redistribution of the remaining Fe3+-ion between A- and B- sites occurs. Magnetization data suggest that the CoAlxFe2-xO4 NPs comprise a homogeneous magnetic core dressed by a spin-glass-like shell. Finally, values of magnetostriction strain sensitivity, much higher than those reported in the literature for the same type of material are estimated in this report, demonstrating that the CoAlxFe2-xO4 NPs constitute promising candidates for applications in stress sensors, actuators, and magnetostrictive filters.

Iron oxide nanoparticles have high saturation magnetization values and their surfaces are easily modified by the insertion of functional groups such as carboxylic acids, surfactants, and polymers. In this work, iron oxide nanoparticles were functionalized with glycerol molecules modified by an esterification reaction with monocarboxylic acid, for their application in the removal of oils in aqueous surface. The nanoparticles were prepared by the coprecipitation method by alkaline hydrolysis of Fe2+ and Fe3+ ions in aqueous medium. The precursor used in the coating was obtained from functionalization of glycerol with stearic acid. The surfaces of iron oxide were coated by two different procedures: i) adding the precursor to the aqueous suspension of the purified iron oxide particles; and ii) preparation, purification and drying of the iron oxide particles and subsequent mixing with the precursor in isopropanol. The results obtained by the FTIR and NMR techniques showed that modification of glycerol with stearic acid occurs by esterification of the primary hydroxyl forming 2,3-dihydroxypropyl stearate. The characterizations carried out in the nanoparticles suggest the presence of cubic structure of inverse spinel, with lattice parameter and stoichiometry close to that of magnetite, which would be described as partially oxidized magnetite. The results obtained by FTIR, TGA and VSM of nanoparticles coated with 2,3-dihydroxypropyl stearate indicate the presence of organic material coating the magnetic nanoparticles. The particles showed certain sphericity with an average size of 11.17 nm and superhydrophobicity (164°). These samples exhibit chemical affinity for oil and are able to move and remove high and low viscosity oils on the water surface by applying an external magnetic field, obtaining an oil removal capacity of about 68 g of Bardahl oil per gram of nanoparticles. In addition, the nanoparticles are easily removed from the oil by a simple treatment with organic solvent, preserving its hydrophobic and oil removal characteristics.

In this study we report on the successful synthesis of Gd x Fe 3− x O 4 nanoparticles with nominal Gd-content ( x ) in the range 0.00≤ x ≤0.50. The effect of the nominal Gd-content on morphological, structural and magnetic properties was investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy and Mossbauer spectroscopy. We found the actual inclusion of Gd 3+ ions into cubic ferrite structure lower than the nominal values, though no extra phase was observed in the whole range of our investigation. Moreover, from Mossbauer data we found evidences of Gd 3+ ions replacing both Fe 3+ and Fe 2+ ions, the latter leading to iron vacancies in the cubic ferrite crystal structure. As the nominal Gd-content, the lattice parameter and the average crystallite size increases monotonically. We found that in the same range of nominal Gd-content the lattice parameter decreases with the increase of iron vacancy content.

In this work hybrids of citric acid doped polyaniline and magnetic iron oxide (MOM) were prepared by in situ chemical polymerization and evaluated in blue methylene dye (MB) adsorption/photodegradation in aqueous medium. The samples were characterized by vibration absorption spectroscopy in the infrared region, X-ray diffraction, thermogravimetric analysis, transmission electron microscopy, Mossbauer spectroscopy, vibration sample magnetometry and electrical conductivity measurements using the four-point method. The characterization results showed that magnetic iron oxide consists of magnetite and maghemite phases with superparamagnetic behavior at room temperature. The hybrids materials present magnetic iron oxide particles dispersed in the polymer phase and electrical conductivity of the order of 10−2S cm−1 and showed adsorbent properties. The adsorption process prevails in relation to the photodegradation, but in the hybrids with higher content of MOM an increase in MB removal was observed under UV irradiation, with reduction of 99% of the dye concentration, indicating synergism between the MOM -polymer phases in the photocatalytic action. These results are related to the hybrids morphology.

The effect of coating with nine different carboxylic acids (glycolic, propionic, lactic, malic, tartaric, citric, mandelic, caproic and caprylic) on nanostructured magnetite (D ~ 10 nm) was studied by Raman and photoacoustic, magnetic and 57Fe Mossbauer measurements. Mossbauer spectra of frozen suspensions showed dominantly magnetically split envelopes at lower temperatures, which were evaluated by hyperfine field distribution method. Mossbauer and Raman spectroscopy indicated similar variation of relative occurrence of magnetite and maghemite phases. These results are discussed on the basis of the hypothesis that different carboxylic acids can promote either the oxidation or reduction of iron oxide nanoparticles.

A simple synthesis method of chitosan functionalized Fe3O4-Au (Chit-Fe2O3@Au) nanoparticles (NPs) was developed. This method first prepared oleic acid-coated Fe3O4 (OA-Fe2O3) NPs as a precursor, followed by functionalization of chitosan to obtain Chit-Fe2O3@Au NPs. Structural and magnetic properties of both synthesized nanomaterials were examined by surface and spectroscopic techniques. An X-ray diffraction (XRD) study showed that the phases of Fe3O4 and Au had sizes of 5.9 and 11.2 nm, respectively. High resolution transmission electron microscopy (HRTEM) images demonstrated the formation of nearly spherical shaped composites in Chit-Fe3O4@Au nanostructures. Energy dispersive X-ray (EDX) spectroscopy measurements confirmed the presence of Au and Fe3O4 in the prepared nanomaterials. The capping of chitosan on Au and Fe3O4 surface was established using Fourier transform infrared (FTIR) spectroscopy measurements. Mossbauer spectra at 300 K showed an increase in superparamagnetic components. At 80 K, the Fe3O4@Au nanomaterials preserved 11% of superparamagnetic phase. Magnetization measurements revealed that the Fe3O4@Au nanomaterials had a saturation magnetization of 28 emu/g at 300 K and a blocking temperature of 117 K. The synthesized nanomaterials have potential in biomedical applications because of their high magnetic property with suitable binding sites for delivering drugs.

Magnetic interaction of the magnetite (Fe3O4) nanoparticles grown on zeolite has been studied. XRD patterns show that in the presence of 25–75 mg of zeolite the average particle size of Fe3O4 decreases to ≈6 nm, but with the increase of zeolite content (75 mg

We have studied the stoichiometry of magnetite nanoparticles using three spectroscopic techniques: Mossbauer, photoacoustic and ferromagnetic resonance (FMR). By varying the weight ratio of the Fe precursor to the reducing agent (sodium acetate) and a post-synthesis annealing, we were able to synthesize samples with different amounts of Fe vacancies, from stoichiometric Fe3O4 to γ-Fe2O3. By synthesizing magnetite in the presence of zeolite we obtained nanoparticles within the 3–10 nm diameter range. The spectroscopic results show that there is a correlation between the amount of Fe vacancies and (i) the optical absorption and (ii) the g-values from the Electron paramagnetic resonance EPR spectra of the nanoparticles.

We have studied LiFePO4/C nanocomposites prepared by sol-gel method using lauric acid as a surfactant and calcined at different temperatures between 600 and 900 °C. In addition to the major LiFePO4 phase, all the samples show a varying amount of in situ Fe2P impurity phase characterized by x-ray diffraction, magnetic measurements, and Mossbauer spectroscopy. The amount of Fe2P impurity phase increases with increasing calcination temperature. Of all the samples studied, the LiFePO4/C sample calcined at 700 °C which contains ∼15 wt% Fe2P shows the least charge transfer resistance and a better electrochemical performance with a discharge capacity of 136 mA h g−1 at a rate of 1 C, 121 mA h g−1 at 10 C (∼70 % of the theoretical capacity of LiFePO4), and excellent cycleability. Although further increase in the amount of Fe2P reduces the overall capacity, frequency-dependent Warburg impedance analyses show that all samples calcined at temperatures ≥700 °C have an order of magnitude higher Li+ diffusion coefficient (∼1.3 × 10−13 cm2 s−1) compared to the one calcined at 600 °C, as well as the values reported in literature. This work suggests that controlling the reduction environment and the temperature during the synthesis process can be used to optimize the amount of conducting Fe2P for obtaining the best capacity for the high power batteries.

– In this study, it was successfully explored the use of resonant X-ray diffraction, with energies tuned to the absorption edges of Zn2+, Fe3+ and Co2+, as an innovative approach to obtain the structural properties of the as-synthesized ZnxCo1-xFe2O4 nanoparticles (NPs) (0.0 ≤ x ≤ 1.0). Zinc-cobalt ferrite, which has potential application in magnetic recording, photo-magnetic devices, biomedicine, gas sensing, catalysis, etc., was synthesized by solution combustion method and analysed by X-ray diffraction, Raman and Mossbauer spectroscopies. Rietveld refinement shows that all samples present single-phase cubic spinel structure (space group F d 3 ¯ m ) with lattice parameter increasing linearly with the Zn-content (x), from 8.37 A to 8.43 A. The data also showed that the average diameter of the crystallites sets around 45 nm and do not depend on the Zn-content. In addition, a complete cationic distribution between A- and B-sublatices was obtained by resonant X-ray diffraction and compared with the partial cationic distribution obtained by Raman and Mossbauer spectroscopies. A strong correlation between the data was found. Despite evidences of the presence of Fe3+-ions in both crystallographic sites, it was found that as the Zn-content increases, Zn2+-ions tend to preferentially occupy A-sites, forcing Fe3+-ions to occupy B-sites. As results, it was observed that with increasing Zn-content, the average distance between cations and anions increases in A-sites (from 1.88 A to 1.98 A) and decreases in B-sites (from 2.06 A to 2.03 A). Resonant X-ray diffraction and Mossbauer data indicate that the replacement of Co2+- by Zn2+-ions changes substantially the NPs’ hyperfine parameters, suggesting that the NPs with intermediate Zn-content present lower crystalline quality while compared to the samples with x = 0.0 and x = 1.0. Evidence of symmetry reduction (from m 3 ¯ m to 3 ¯ m ) in the B-sites was obtained, which is in accordance with the variation verified in the integrated areas and energies found for the Raman modes below 600 cm−1. Finally, the excellent agreement between the results obtained by resonant X-ray diffraction, Raman spectroscopy and Mossbauer spectroscopy indicate the robustness of the approach herein used to assess the cation distribution in quaternary spinel ferrites.

Enhancing the rate of decomposition or removal of organic dye by designing novel nanostructures is a subject of intensive research aimed at improving waste-water treatment in the textile and pharmaceutical industries. Despite radical progress in this challenging area using iron-based nanostructures, enhancing stability and dye adsorption performance is highly desirable. In the present manuscript alkali cations are incorporated into iron oxide nanoparticles (IONPs) to tailor their structural and magnetic properties and to magnify methyl blue (MB) removal/decomposition capability. The process automatically functionalizes the IONPs without any additional steps. The plausible mechanisms proposed for IONPs incubated in alkali chloride and hydroxide solutions are based on structural investigation and correlated with the removal/adsorption capabilities. The MB adsorption kinetics of the incubated IONPs is elucidated by the pseudo second-order reaction model. Not only are the functional groups of –OH and –Cl attached to the surface of the NPs, the present investigation also reveals that the presence of alkali cations significantly influences the MB adsorption kinetics and correlates with the cation content and atomic polarizability.

Magnetic nanoparticles have been of great scientific interest because of their possible industrial and biomedical applications. The magnetic iron oxide was synthesized by the co precipitation of alkaline hydrolysis of ions Fe2+ and Fe3+ in aqueous system. The coated particles were obtained by heating (50 and 250 °C) mixed magnetic iron oxide and polydimethylsiloxane oil for 30 min obtaining magnetic dust particles with hydrophobic behavior. These were used to learn the dragging effects and removal of nonpolar organic compound in aqueous systems. The samples were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), chemical analysis by potenciometric titration, thermogravimetric analysis (TGA), transmission electron microscopy (TEM), vibrating sample magnetometry (VSM), contact angle measurement and Mossbauer spectroscopy. The diffractogram of X-ray presented peaks that were assigned to presence of spinel structure maghemite and magnetite with medium sized crystallites of 10.95 nm for the polymeric coated magnetic iron oxide, confirmed by TEM, with superparamagnetic character, also confirmed by VSM. The infrared spectrum showed absorption band at 570 cm−1 characteristic of the Fe-O bonding in inverted spinel structure and the absorption bands in 1263, 1105, 1025 and 800 cm−1 indicating the presence of PDMS on the magnetic iron oxide particles. Thermogravimetric analysis has been used to estimate the sample thermal stability of polymeric material (9.7 ± 4) % on the inorganic matrices. Contact angle measurement of the coated samples at 250 °C presented a better nonpolar character in comparison to the coated samples at 50 °C. The samples at room temperature (25 °C) presented the phases of magnetite and maghemite which were also confirmed by Mossbauer spectroscopy. It was possible to obtain iron oxides particles coated with PDMS, with hydrophobic and magnetic properties, which slide over the water surface when magnetic field is applied. This character was used successfully, by testing, for removal of small fraction vegetable oil on the water surface.

57Fe Mossbauer spectroscopy, XRD, and TEM were used to investigate the effect of mandelic- and salicylic acid coatings on the iron oxide nanoparticles. These two carboxylic acids have similar molecules size and stoichiometry, but different structure and acidity. Significant differences were observed between the Mossbauer spectra of samples coated with mandelic acid and salicylic acid. These results indicate that the occurrence of iron microenvironments in the mandelic- and salicylic acid-coated iron oxide nanoparticles is different. The results can be interpreted in terms of the influence of the acidity of carboxylic acids on the formation, core/shell structure, and oxidation of coated iron oxide nanocomposites.

The structural and hyperfine properties of bulk TiFe0.5Ni0.5 intermetallic and ball-milled TiFe0.5Ni0.5/graphite compounds and their hydrides have been studied. The bulk and nanostructured TiFe0.5Ni0.5 compounds crystallize in the cubic crystal structure of CsCl (B2). After hydrogenation, the formation of hydrogen-poor phase (∝-phase) and hydride phase (β-phase) have been determined for the bulk compound. However, the formation of the ∝-phase and the hydrogen-richest phase (γ-phase) and other secondary phases have been determined for the ball-milled TiFe0.5Ni0.5/graphite sample. It has been determined that the ball-milled TiFe0.5Ni0.5/graphite sample presents a large amount of the γ-phase which indicates that the presence of graphite nearby nanostructured intermetallic grains enhances the absorption of hydrogen. Mossbauer results are consistent with the structural results. Meanwhile, no significant changes in the isomer shift (IS) value has been determined for the α-phase with respect to the intermetallic compound, a strong increase in the IS value has been determined for the β- and γ-phases with respect to the ∝-phase. That increase indicates a decrease of the s-electron density at the Fe nuclei due to the charge transfer from the metal to the nearby hydrogen atoms.

The effect of Lithium insertion in the crystal structure and magnetic properties of Barbosalite [Fe3(PO4)2(OH)2], a polymorph of iron hydroxyl phosphate synthesized from variable Fe precursor (Fe(II) and Fe(III)), have been investigated. Effect of distortion in the crystal structure of Barbosalite appeared with minimum lithium hydroxide (LiOH.H2O) concentration of 0.5 M as depicted from the XRD patterns. Further, appearance of fresh peaks from 2 M is well matched with the crystal structure of LiFePO4. Studies with Mossbauer spectroscopy and SQUID Magnetometer intriguingly reveals that Li intercalation in the barbosalite affects only Fe(III) sites whereas the Fe(II) sites remains unaffected till 2 M. However, further increase in the Li concentration leads to structural transformation and results in LiFePO4 phase. Comparative studies of the structural and magnetic properties, magnetic transition are also discussed.

A series of novel [Fe(MeiPrGlyoxH)2(amine)2] complexes have been synthesized [(MeiPrGlyoxH2 = methylisopropylglyoxime, amine = 3,5-dimethylpyridine, 4-(dimethylamino)pyridine, 4-(phenylamino)phenol, 2-imidazolidone)] and characterized by 57Fe Mossbauer, FTIR, UV–Vis spectroscopy, mass spectrometry, AFM and thermoanalytical methods. Quantum chemical (DFT) computations of [Fe(MeiPrGlyoxH)2(3,5-dimethyl-Py)2] (Py = pyridine) complex were also performed. The square-planar structure of [Fe(MeiPrGlyoxH)2] moiety is similar to that of [Fe(MeEtGlyoxH)2]. The incorporation of branching alkyl chains (isopropyl) in the complexes alters the Fe–N bond length and results in high-spin iron(II) state.

Bare Fe3O4 and Fe3O4/zeolite composites have been investigated by Mossbauer spectroscopy. A confined growth of the nanoparticles has been observed after introduction of zeolite in the process of precipitation. Increase in the concentration of zeolite further decrease the particle size. A comparative study on the synthesis with zeolites 13x and ZSM5 has been done. Annealing on these nanoparticles shows that apart from the confinement of nanoparticles, zeolite enhances stability on the nanoparticles.

The application of lithium iron phosphate as positive electrode material for lithium ion batteries has been challenged by its poor electronic conductivity. To improve its conductivity and electrochemical performance, we have synthesized LiFePO4/C composite cathode materials by sol gel technique using long chain fatty acids, such as, lauric, myristic, and oleic acids, as surfactants for carbon coating. The phase purity of the three LiFePO4/C composites was confirmed by X-ray diffraction. The Raman spectroscopy, scanning electron microscopy and transmission electron microscopy measurements show that the surfactants coat the LiFePO4 particles with carbon with varying degree of uniformity depending on the surfactant used. The sample prepared in presence of lauric acid shows smaller particle size and the lowest charge transfer resistance, higher Li-ion diffusion coefficient, higher discharge capacity (w155 mAh g � 1 at C/3 rate), better rate capability and cyclic stability compared to the other two samples. We found the smaller particle size, uniformity of carbon coating, reduced agglomeration, and a lower amount of Fe 3þ impurity phase in the samples to be major contributing factors for better electrochemical

The present study describes the synthesis and characterization of iron@iron oxide nanoparticles produced by passivation of metallic iron in tetraethylene glycol media. Structural and chemical characterizations were performed using transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Mössbauer spectroscopy. Pomegranate-like core@shell nanoparticulate material in the size range of 90–120nm was obtained. According to quantitative phase analysis using Rietveld structure refinement the synthesized iron oxide was identified as magnetite (Fe3O4) whereas the iron to magnetite mass fractions was found to be 47:53. These findings are in good agreement with the data obtained from Mössbauer and thermal gravimetric analysis (TGA). The XPS data revealed the presence of a surface organic layer with higher hydrocarbon content, possibly due to the tetraethylene glycol thermal degradation correlated with iron oxidation. The room-temperature (300K) saturation magnetization measured for the as-synthesized iron and for the iron–iron oxide were 145emug−1 and 131emug−1, respectively. The measured saturation magnetizations are in good agreement with data obtained from TEM, XRD and Mössbauer spectroscopy.

We report the synthesis of LiFePO 4 /graphene nano-composites using sol–gel method in the presence of dispersed graphene oxide mixed with LiFePO 4 precursors. The phase purity of the nano-LiFePO 4 /graphene composite was confirmed by X-ray diffraction. The electronic conductivity of LiFePO 4 /graphene composite was found to be six orders of magnitude higher than that of pure LiFePO 4 synthesized following otherwise the same procedure without the addition of graphene. Scanning electron microscopy and transmission electron microscope images show LiFePO 4 particles being covered uniformly by graphene sheets throughout the material forming a three-dimensional conducting network. At low currents and charging rate of C/3, the capacity of the composite cathode reaches 160 mAh/g, which is very close to the theoretical limit. More significantly, the LiFePO 4 –graphene composite shows a dramatically improved rate capability up to 27 C and excellent charge–discharge cycle stability over 500 stable cycles in comparison with the LiFePO 4 without graphene.

We report on the synthesis and characterization of uncoated and gold coated magnetite nanoparticles. Structural characterizations, carried out using X-ray diffraction, confirm the formation of magnetite phase with a mean size of ~7 and ~8 nm for the uncoated and gold covered magnetite nanoparticles, respectively. The value of the gold coated Fe3O4 nanoparticles is consistent with the mean physical size determined from transmission electron microscopy images. Mossbauer spectra at room temperature are consistent with the thermal relaxation of magnetic moments mediated by particle-particle interactions. The 77 K Mossbauer spectra are modeled with four sextets. Those sextets are assigned to the signal of iron ions occupying the tetrahedral and octahedral sites in the core and shell parts of the particle. The room-temperature saturation magnetization value determined for the uncoated Fe3O4 nanoparticles is roughly ~60 emu/g and suggests the occurrence of surface effects such as magnetic disorder or the partial surface oxidation. These surface effects are reduced in the gold-coated Fe3O4 nanoparticles. Zero-field–cooled and field-cooled curves of both samples show irreversibilities which are consistent with a superparamagnetic behavior of interacting nanoparticles.

In this work we present the study of hematite (α-Fe2O3) nanostructures synthesized by the ball milling technique. The structural characterization and the crystallite size estimation have been carried out using the X-ray diffraction (XRD) technique. Data analyses indicate that the hematite phase (space group, R-3C) is preserved after the milling process. As the milling time is increased, a second phase (α-Fe) appears. The mean crystallite size shows a decreasing tendency as the milling time is increased. High-resolution transmission electron microscopy (HRTEM) images show the formation of grains composed of crystallites with irregular shapes. Mossbauer spectra of milled powders carried out at 297 and 77 K are well modeled with a histogram distribution of hyperfine fields. The presence of one additional sextet which corresponds to the ∝-Fe phase is also determined in agreement with XRD data analysis. Magnetic measurements suggest the suppression of the Morin transition in the milled samples and the absence of thermal relaxation effects in agreement with the Mossbauer spectroscopy results.

Samples of 40SiO 2 ·30Na 2 O·1Al 2 O 3 ·(29 − x )B 2 O 3 · x Fe 2 O 3 (mol%), with 0.0 ≤ x ≤ 17.5, were prepared by the fusion method and investigated by electron paramagnetic resonance (EPR), optical absorption (OA) and Mossbauer spectroscopy (MS). The EPR spectra of the as-synthesized samples exhibit two well-defined EPR signals around g = 4.27 and g = 2.01 and a visible EPR shoulder around g = 6.4, assigned to isolated Fe 3+ ion complexes ( g = 4.27 and g = 6.4) and Fe 3+ -based clusters ( g = 2.01). Analyses of both EPR line intensity and line width support the model picture of Fe 3+ -based clusters built in from two sources of isolated ions, namely Fe 2+ and Fe 3+ ; the ferrous ion being used to build in iron-based clusters at lower x -content (below about x = 2.5%) whereas the ferric ion is used to build in iron-based clusters at higher x -content (above about x = 2.5%). The presence of Fe 2+ ions incorporated within the glass template is supported by OA data with a strong band around 1100 nm due to the spin-allowed 5 E g – 5 T 2g transition in an octahedral coordination with oxygen. Additionally, Mossbauer data (isomer shift and quadrupole splitting) confirm incorporation of both Fe 2+ and Fe 3+ ions within the template, more likely in tetrahedral-like environments. We hypothesize that ferrous ions are incorporated within the glass template as FeO 4 complex resulting from replacing silicon in non-bridging oxygen (SiO 3 O − ) sites whereas ferric ions are incorporated as FeO 4 complex resulting from replacing silicon in bridging-like oxygen silicate groups (SiO 4 ).

Nanosized maghemite (below 10 nm average diameter), surface-functionalized with meso-2,3-dimercaptosuccinic acid (DMSA), was investigated with respect to the content of DMSA molecules attached onto its surface and the onset of S-S bridges due to oxidation of neighboring S-H groups. To support our investigation, we introduced the use of photoacoustic spectroscopy to monitor thiol groups (S-H) conjugated with Raman spectroscopy to monitor the disulfide bridges (S-S). The normalized intensity (N(R)) of the Raman feature peaking at 500 cm(-1) was used to probe the S-S bridge whereas the normalized intensity (N(P)) of the photoacoustic band-S (0.42-0.65 μm) was used to probe the S-H moiety. The perfect linearity observed in the N(R) versus (1 - N(P)) plot strongly supports the oxidation process involving neighboring S-H groups as the DMSA surface grafting coefficient increases whereas the approach used in this report allows the evaluation of the [S-H]/[S-S] ratio. The observation of the reduction of the hydrodynamic diameter as the nominal DMSA-grafting increases supports the proposed model picture, in which the intraparticle (interparticle) S-S bridging takes place at higher (lower) DMSA-grafting values.

In this study photoacoustic spectroscopy was used to investigate the effect of dilution of an oil-based magnetic fluid sample on the magnetic nanoparticle surface-coating. Changes of the photoacoustic signal intensity on the band-L region (640 to 830 nm) upon dilution of the stock magnetic fluid sample were discussed in terms of molecular surface desorption. The model proposed here assumes that the driving force taking the molecules out from the nanoparticle surface into the bulk solvent is the gradient of osmotic pressure. This gradient of osmotic pressure is established between the nanoparticle surface and the bulk suspension. It is further assumed that the photoacoustic signal intensity (area under the photoacoustic spectra) scales linearly with the number of coating molecules (surface grafting) at the nanoparticle surface. This model picture provides a non-linear analytical description for the reduction of the surface grafting coefficient upon dilution, which was successfully-used to curve-fit the photoacoustic experimental data.

Photoacoustic spectroscopy is introduced as a promising experimental technique to investigate fungus infected Acai (Euterpe oleracea) seeds. Photoacoustic spectra of healthy and infected Acai seeds with the fungus Colletotrichum gloeosporioides were recorded firstly in the modulation frequency range of 5Hz to 700 Hz, while keeping the wavelength of excitation radiation of a Xe arc-lamp constant, to ascertain the depth of penetration of infection within the seed and secondly, at variable wavelength (wavelength scanning) in the interval 250nm to 1,000 nm, while keeping the modulation frequency constant. In the former, the photoacoustic signal strength from the infected seed was found higher than that of the healthy one, and has been associated with the appearance of new biomolecules associated with the pathogen infection. In the latter, characteristics peaks and bands were observed in the range from 650 nm to 900 nm ascribed to organic compounds with carboxylates and amines (functional groups) forming the typical metabolic structures of the fungus.

Mossbauer and magnetic characterization of polymer-dispersed γ-Fe2O3 nanoparticles treated under different chemical processes are reported in this work. X-ray powder diffraction analysis provides a mean particle size of D ~ 8.0 nm. Whereas Mossbauer spectroscopy data suggest the presence of only Fe3 + ions, magnetization measurements indicate the occurrence of a freezing phenomenon in agreement with the thermal evolution of Mossbauer spectra. A core–shell model was used to determine a magnetically disordered layer (shell) of d ~ 1.0 nm covering a region of collinear magnetic moments (core). The chemical treatments with H2O2 and Na2S2O8 modify notoriously the magnetic response of the polymer-dispersed nanoparticles.

In this study the synthesis of very small magnetite nanoparticles is reported. Analysis of the (311) X-ray diffraction line indicates nanoparticle with 2.2 nm average diameter. The as-synthesized nanosized magnetite sample was submitted to a chemical oxidation process for conversion to maghemite. However, the yielding of the chemical oxidation process, as indicated by the analysis of the Mossbauer data, was about 20%. This finding indicates a strong size-dependence of the oxidation process, reducing the yielding of the chemical process used as the nanoparticle size reduces down to extremely low values.

Biocompatible magnetic nanocomposite consisting of bovine serum albumin-based nanosized spheres hosting maghemite nanoparticle has been investigated by Mossbauer spectroscopy, X-ray diffraction, and electron microscopy. The 77 K Mossbauer spectrum was curve-fitted to two sextets whereas one doublet plus one sextet was used to fit the 300 K Mossbauer spectrum. The temperature evolution of the hyperfine parameters indicated two Mossbauer components; one associated to the core maghemite nanoparticle and the other associated to the maghemite surface shell. The 300 K quadrupole splitting value indicated strong interaction between the surface of the maghemite nanoparticle and the hosting template.

The chemical co-precipitation process was used to synthesize (in situ) spherical iron-oxide nanoparticle in sulfonated styrene-divinylbenzene polymeric template. X-ray diffraction technique supports the magnetite phase formation with a mean particle diameter of about 19 nm. The analysis of Mossbauer spectra is consistent with two magnetic splitting patterns assigned to A- and B-iron sites of magnetite, with no visible magnetic relaxation effect even at 297 K. Considering the different experimental time window between Mossbauer spectroscopy and DC magnetization, the results obtained from both techniques are in very good agreement. Magnetic data suggest hosting magnetite nanoparticles interacting antiferromagnetically.

Room-temperature measurements of the magnetic susceptibility of Bovine Serum Albumin-based nanocapsules (50 to 300 nm in size) loaded with different amounts of maghemite nanoparticles (7.6 nm average diameter) have been carried out in this study. The field (H) dependence of the imaginary peak susceptibility (fP) of the nanocomposite samples was investigated in the range of 0 to 4 kOe. From the analysis of the fP × H curves the concentration (N) dependence of the effective maghemite magnetocrystalline energy barrier (E) was obtained. Analysis of the E × N data was performed using a modified Mørup-Tronc [Phys. Rev. Lett. 72, 3278 (1994)] model, from which a huge contribution from the magnetocrystalline surface anisotropy was observed.

In this study we demonstrate the usefulness of the Photoacoustic Spectroscopy (PAS) in the investigation of copaiba oil obtained from Copaifera tree, located in a site within Rondonia State, Amazon region, Brazil. Pure copaiba oil sample was diluted in 98% ethanol providing 10 different samples at volume concentration in the range of 5 to 50% vv. The observed photoacoustic spectral features from pure copaiba oil and the corresponding diluted samples, in the 0.18 to 4.00 μm wavelength region, are discussed in terms of five distinct bands (C, S, L, K, and X bands). Photoacoustic peak intensity was investigated as a function of the copaiba oil concentration in the 5 to 50% v.v.

Photoacoustic spectroscopy (PAS) was used to investigate samples produced from Baru (Dipteryx alata Vog.), a typical fruit from the Brazilian Cerrado, which is considered as a good source of nutrients. The photoacoustic (PA) spectra of samples prepared from Baru seeds present three different absorption bands in the wavelength range 0.3–1.0 μm, named Band-C, Band-S, and Band-L. We found that PAS can be useful for monitoring the strong absorption of visible light by Baru's seeds constituents mainly in the shorter wavelength measured range. This study is important from both agricultural and commercial point of view once it introduces PAS as a potential characterization technique allowing better control of fruit and seed selection, storage and transportation.

In this study we demonstrate the usefulness of the Photoacoustic Spectroscopy (PAS) in the investigation of water collected from a natural site located within the Amazon region, Brazil, during the wet to dry seasons transition (May/2006). The water samples were collected from different stages along a hydrologic pathway including precipitation water (Prec), groundwater (GW), through flow water (TF), overland flow water (OF), and stream flow water (SW). The observed photoacoustic spectral features, in the 0.3 to 1.0 μm wavelength region, fall within three distinct bands (C, S, and L). We found band-C, band-S and band-L occurring in the spectral range of 0.30 to 0.40 μm, 0.40 to 0.45 μm and 0.45 to 1.0 μm regions, respectively. The photoacoustic features shift peak positions and change intensities for all samples investigated, thus supporting the proposal of PAS as a useful technique to investigate water samples from natural environments.

Studies of superparamagnetic iron oxide nanoparticles (SPIONs) have been extensively carried out. Since the earlier work on Mossbauer studies on SPIONs in 1970s, many biomedical applications and their uses in innovative methods to produce new materials with improved performance have appeared. Applications of SPIONs in environmental remediation are also forthcoming. Several different methods of synthesis and coating of the magnetic particles have been described in the literature, and Mossbauer spectroscopy has been an important tool in the characterization of these materials. It is quite possible that the interpretation of the Mossbauer spectra might not be entirely correct because the possible presence of maghemite in the end product of SPIONs might not have been taken into consideration. Nanotechnology is an emerging field that covers a wide range of new technologies under development in nanoscale (1 to 100 nano meters) to produce new products and methodology.

In this study γ-Fe 2 O 3 nanoparticle, surface-coated with increasing amount of oleic acid, have been prepared while the stability against particle degradation under laser excitation intensity was investigated. Maghemite nanoparticle was obtained via oxidation of magnetite nanoparticle, the latter synthesized by co-precipitation of Fe (II) and Fe (III) ions in alkaline medium. By varying the experimental conditions of surface-coating maghemite nanoparticles with oleic acid, samples with different grafting coefficient were obtained and investigated using X-ray diffraction and different spectroscopic techniques, namely Raman, Mossbauer, and infrared. The amount of oleic acid adsorbed on the maghemite surface was estimated via the carbon content obtained from elemental analysis.

In this study cobalt ferrite nanoparticles were synthesized in a macroporous styrene–divinylbenzene copolymer template. Aqueous solutions containing Fe3 + and Co2 + ions (2:1 ratio) were retained in the template’s pores. The metal ions were precipitated inside the template using alkaline solution. In order to improve nanophase crystallinity samples were treated under different conditions; in air atmosphere and in nitrogen atmosphere, at 150°C or 300°C, for 2 or 4 h. All materials were characterized by chemical analysis, infrared spectroscopy, X-ray diffraction, and Mossbauer spectroscopy. We found improvement of the nanoparticles’ crystallinity only after thermal treatments in air atmosphere whereas the polymer structure was modified only in air atmosphere and at higher temperature.

In this study, we report on how surface-passivated and nonpassivated cobalt ferrite nanoparticles (8 nm diameter), suspended as ionic magnetic fluids and aged under low pH conditions, revealed different behavior as far as the time evolution of the iron/cobalt cation distribution, crystal quality, coercivity, and saturation magnetization are concerned. Different techniques were used to perform a detailed study regarding the chemical stability, structural stability, and surface and magnetic properties of the suspended nanoparticles as a function of the aging time. Properties of surface-passivated and nonpassivated nanoparticles were investigated by transmission electron microscopy, X-ray diffraction, atomic absorption spectrometry, magnetic measurements, Raman spectroscopy, and Mössbauer spectroscopy. Our data showed that the employed nanoparticle surface passivation process, besides the formation of an iron-rich surface layer, modifies the nanoparticle core as well, improving the crystal quality while modifying the Fe/Co cation distribution and the nanoparticle dissolution rate profile. Magnetic data showed that the saturation magnetization increases for surface-passivated nanoparticles in comparison to the nonpassivated ones, though coercivity decreases after passivation. These two observations were associated to changes in the cation distribution among the available tetrahedral and octahedral sites.

Magnetic characterization of maghemite nanoparticles dispersed in a polymeric template and treated under different chemical processes is reported in this work. Particle size estimated from magnetic measurements, DM ≈ 10 nm, for the free-surfactant sample, is consistent with values determined from XRD analysis and TEM images. The magnetic collapse of sextets towards a quadrupole doublet as the temperature is increased reveals the thermal relaxation of smaller ψ-Fe203 nanoparticles. Magnetic measurements show a strong irreversibility between ZFC and FC curves suggesting the occurrence of particle-particle interaction.

Transmission electron microscopy, X-ray diffraction and Mossbauer spectroscopy were used in the characterization of a nanocomposite containing magnetic nanoparticles dispersed in a glycolic acid-based template. Maghemite nanoparticles were identified as the iron oxide phase dispersed in the polymeric template. From the low-temperature Mossbauer data the amount of the iron-based, non-magnetic material at the nanoparticle surface was estimated as roughly one monolayer in thickness.

Mossbauer spectroscopy was used in this study to investigate magnetite-based nanocomposites, using mesoporous styrene-divinylbenzene (Sty-DVB) microspheres as the hosting template. The magnetite content was increased in the polymeric template by performing several in situ chemical reactions (one to six cycles) in the hosting material. We found the Mossbauer linewidth associated to site-A increasing with the relative increase of iron in site-A. The Mossbauer linewidth associated to site-B decreases with the relative decrease of iron in site-B. We explain our findings by assuming local change in the homogeneity associated to changes in the relative iron population in sites A and B.

Nucleation and growth mechanism of iron oxide nanoparticles on zeolite template and their stability dependence are reported. Hyperfine field resulting from the variation of particle size indicates the effect of zeolite on particles growth; particle size decreases at lower concentration of zeolite. At higher concentration, a fraction of nano Fe3O4 experiences hyperfine field (45 and 49 T) similar to bulk particles. Effect of incubation and digestion time on the particles growth and the binding effect with zeolite are discussed. Annealing treatments show that the binding of nanoparticles with zeolite stabilizes the nanoparticles with regard to agglomeration and structural transformation. Thermogravimetry-differential thermal analysis (TG-DTA) shows that increase in dehydration temperature from 335.1 to 351.7 K results in zeolite content increasing from 0 to 1000 mg. Weight loss of the particles prepared in incubation time of 0.5 min is 9.46% and reaches 13.9% in 240 min. The weight loss remains practically constant at ca. 9% irrespective of the digestion method.