Nanoscaled biocompatible magnetic drug-delivery system: preparation and characterization

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 Mössbauer 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 Mössbauer spectroscopy and DC magnetization, the results obtained from both techniques are in very good agreement. Magnetic data suggest hosting magnetite nanoparticles interacting antiferromagnetically.     

Separation of Contributions of the Magnetic Relaxation and Diffusion of Nanoparticles in Ferrofluids by Analyzing the Hyperfine Structure of Mössbauer Spectra

The theory and method for analysis of Mössbauer spectra of magnetic nanoparticles in a fluid have been developed by generalizing the model of the magnetic dynamics of a Néel ensemble of antiferromagnetic particles to the case of ferrimagnetic iron oxides. The resulting model describing the “superposition” of the magnetic dynamics and translational motion of nanoparticles in ferrofluids has been tested in application to the simultaneous analysis of Mössbauer spectra of “dry” magnetite nanoparticles and the same particles in glycerol.     

Magnetic and Mössbauer studies of fucan-coated magnetite nanoparticles for application on antitumoral activity

Fucan-coated magnetite (Fe₃O₄) nanoparticles were synthesized by the co-precipitation method and studied by Mössbauer spectroscopy and magnetic measurements. The sizes of the nanoparticles were 8–9 nm. Magnetization measurements and Mössbauer spectroscopy at 300 K revealed superparamagnetic behavior. The magnetic moment of the Fe₃O₄ is partly screened by the Fucan coating aggregation. When the magnetite nanoparticles are capped with oleic acid or fucan, reduced particle-particle interaction is observed by Mössbauer and TEM studies. The antitumoral activity of the fucan-coated nanoparticles were tested in Sarcoma 180, showing an effective reduction of the tumor size.     

Magnetite nanoparticles as-prepared and dispersed in Copaiba oil: study using magnetic measurements and Mössbauer spectroscopy

Study of magnetite nanoparticles, as-prepared and dispersed in Copaiba oil as magnetic fluid, by means of magnetic measurement and Mössbauer spectroscopy at various temperatures demonstrated differences in the saturation magnetization and Mössbauer hyperfine parameters which were related to the interactions of Copaiba oil polar molecules with iron cations on magnetite nanoparticle’s surface.     

Mössbauer and magnetic studies of MFe2O4(M = Co, Ni) nanoparticles

Nanocrystalline MFe₂O₄ (M?=?Co, Ni) particles are synthesized by citrate precursor technique. Mössbauer and magnetic studies are carried out with the CoFe₂O₄ samples having particle sizes of 9, 14 and 30 nm and the NiFe₂O₄ samples having particle sizes of 9, 21 and 30 nm. The intrinsic magnetic parameters are found to vary with the particle size. The magnetic interactions and cation distribution present in these systems influence the room temperature Mössbauer parameters. Ferrimagnetic sextets are observed for all the different particle sizes. The observed reduction of the magnetic hyperfine field values with the decrease in the size of MFe₂O₄ particles are attributed to the intrinsic size effect and the canted spin structure at the surface of the nanoparticles.     

Magnetic composites from minerals: study of the iron phases in clay and diatomite using Mössbauer spectroscopy, magnetic measurements and XRD

Magnetic particles as matrix for enzyme immobilization have been used and due to the enzymatic derivative can be easily removed from the reaction mixture by a magnetic field. This work presents a study about the synthesis and characterization of iron phases into magnetic montmorillonite clay (mMMT) and magnetic diatomaceous earth (mDE) by ⁵⁷Fe Mössbauer spectroscopy (MS), magnetic measurements and X-ray diffraction (XRD). Also these magnetic materials were assessed as matrices for the immobilization of invertase via covalent binding. Mössbauer spectra of the magnetic composites performed at 4.2 K showed a mixture of magnetite and maghemite about equal proportion in the mMMT, and a pure magnetite phase in the sample mDE. These results were verified using XRD. The residual specific activity of the immobilized invertase on mMMT and mDE were 83 % and 92.5 %, respectively. Thus, both magnetic composites showed to be promising matrices for covalent immobilization of invertase.     

Iron oxide nanoparticles for plant nutrition? A preliminary Mössbauer study

One of the most important micronutrients for plants is iron. We have prepared iron(III) oxyhydroxide and magnetite nanoparticles with the aim to use them as possible nutrition source for plants. The iron(III)-oxide/oxyhydroxide nanoparticles prepared under our experimental conditions as colloidal suspensions proved to be 6-line ferrihydrite nanoparticles as verified by XRD, TEM/SAED and Mössbauer spectroscopy measurements. ⁵⁷Fe Mössbauer spectra of magnetite nanoparticles prepared under different preparation conditions could be analyzed on the basis of a common model based on the superposition of four sextet components displaying Gaussian-shaped hyperfine magnetic field distributions.     

Mössbauer spectroscopy study of iron oxide nanoparticles obtained by spray pyrolysis

Mössbauer spectroscopy was used in this study to investigate magnetite nanoparticles, obtained by spray pyrolysis and thermal treatment under H₂ reduction atmosphere. Room temperature XRD data indicate the formation of magnetite phase and a second phase (metallic iron) which amount increases as the time of reduction under H₂ is increased. While room temperature Mössbauer data confirm the formation of the cubic phase of magnetite and the occurrence of metallic iron phase, the more complex features of 77 K-Mössbauer spectra suggest the occurrence of electronic localization favored by the different crystalline phase of magnetite at low temperatures which transition to the lower symmetry structure should occur at T ～120 K (Verwey transition).     

Synthesis and characterization of uncoated and gold-coated magnetite nanoparticles

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. Mössbauer spectra at room temperature are consistent with the thermal relaxation of magnetic moments mediated by particle-particle interactions. The 77 K Mössbauer 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.     

Mössbauer spectroscopy,dispersion and catalysis

A first part presents and discuss the peculiarities of Mössbauer parameters arising from particle sizes smaller than some tens of nanometers, linewidth, isomer shift, quadrupole interaction, magnetic behaviour,f-factor value and anisotropy. In a second part examples are detailed where catalysts powders during reaction underwent changes in particles sizes, which could be studied by Mössbauer spectroscopy: dispersion increase resulting from iron carburization in Fischer-Fropsch synthesis, changes in particle sizes of iron- or tin-based catalysts used for coal hydroliquefaction.     

M?ssbauer study of carbon coated iron magnetic nanoparticles produced by simultaneous reduction/pyrolysis

Magnetic iron nanoparticles immersed in a carbon matrix were produced by a combined process of controlled dispersion of Fe^3?+? ions in sucrose, thermal decomposition with simultaneous reduction of iron cores and the formation of the porous carbonaceous matrix. The materials were prepared with iron contents of 1, 4 and 8 in %wt in sucrose and heated at 400, 600 and 800°. The samples were analyzed by XRD, Mössbauer spectroscopy, magnetization measurements, TG, SEM and TEM. The materials prepared at 400° are composed essentially of Fe₃O₄ particles and carbon, while treatments at higher temperatures, e.g. 600 and 800° produced as main phases Fe⁰ and Fe₃C. The Mössbauer spectra of samples heated at 400° showed two sextets characteristic of a magnetite phase and other contributions compatible with Fe^3?+? and Fe^2?+? phases in a carbonaceous matrix. Samples treated at temperatures above 600° showed the presence of metallic iron with concentrations between 16?C43%. The samples heated at 800° produced higher amounts of Fe₃C (between 20% and 58%). SEM showed for the iron 8% sample treated at 600?C800°C particle sizes smaller than 50 nm. Due to the presence of Fe⁰ particles in the carbonaceous porous matrix the materials have great potential for application as magnetic adsorbents.     

Mössbauer study of a Fe3O4/PMMA nanocomposite synthesized by sonochemistry

Magnetite nanoparticles of 10 nm average size were synthesized by ultrasonic waves from the chemical reaction and precipitation of ferrous and ferric iron chloride (FeCl₃ · 6H₂O y FeCl₂ · 4H₂O) in a basic medium. The formation and the incorporation of the magnetite in PMMA were followed by XRD and Mössbauer Spectroscopy. These magnetite nanoparticles were subsequently incorporated into the polymer by ultrasonic waves in order to obtain the final sample of 5 % weight Fe₃O₄ into the polymethylmethacrylate (PMMA). Both samples Fe₃O₄ nanoparticles and 5 % Fe₃O₄/PMMA nanocomposite, were studied by Mössbauer spectroscopy in the temperature range of 300 K–77 K. In the case of room temperature, the Mössbauer spectrum of the Fe₃O₄ nanoparticles sample was fitted with two magnetic histograms, one corresponding to the tetrahedral sites (Fe^3?+?) and the other to the octahedral sites (Fe^3?+? and Fe^2?+?), while the 5 % Fe₃O₄/PMMA sample was fitted with two histograms as before and a singlet subspectrum related to a superparamagnetic behavior, caused by the dispersion of the nanoparticles into the polymer. The 77 K Mössabuer spectra for both samples were fitted with five magnetic subspectra similar to the bulk magnetite and for the 5 % Fe₃O₄/PMMA sample it was needed to add also a superparamagnetic singlet. Additionally, a study of the Verwey transition has been done and it was observed a different behavior compared with that of bulk magnetite.     

Mechanochemical and magnetomechanical synthesis of hematite nanoparticles

Samples of hematite were exposed to mechanochemical activation by high energy ball milling for 0–27 h. The milling-induced changes to the structural and magnetic properties of hematite were characterized by X-ray diffraction (XRD) and Mössbauer spectroscopy. The particle size was found to decrease from 80 to 16.5 nm after 8 h of ball milling time, followed by a small increase to 19.8 nm at the end of the milling period. An overall expansion of the crystalline lattice parameters a and c with the milling time was deduced. The magnetic hyperfine field decreased with the ball milling time, from 51.46 down to 50.68 T after 27 h of grinding. Magnetite and traces of iron were observed at the longest milling time employed. The recoilless fraction (f ) was measured simultaneously using a dual Mössbauer absorber consisting of hematite and a stainless steel etalon. The f factor first decreased with the milling time due to occurrence of nanoparticles in the system, had a maximum at 12 h due to agglomerations of nanoparticles and exhibited a second maximum at 27 h, due to the appearance of magnetite in the system. More samples of hematite were subjected to magnetomechanical activation by magnetic ball milling for 52 and 134 h. A phase mixture of hematite and magnetite was observed.     

Effect of particle size and alloying with different metals on 57Fe Mössbauer spectra

Iron nanoparticles of various sizes have been synthesized using the chemical route which involves the preparation of iron bipyridine complexes in presence of different capping agents followed by thermal decomposition at 450°C in inert atmosphere. The bimetallic nanoalloys of Fe with Mg and Pd have also been prepared by following the same route. The resulting nanoparticles have been characterized by EDX-RF, XRD, AFM and ⁵⁷Fe Mössbauer spectroscopy. The appearance of quadrupole doublets in the Mössbauer spectra of Fe nanoparticles indicates the absence of magnetic interaction and variation in parameters is due to the varying particle size. The Mössbauer spectrum of Fe–Mg₂ bimetallic nanoalloy shows two doublets indicating the presence of superparamagnetism. The two doublets can be attributed to change in s-electron density of iron resulting from its two neighboring magnesium atoms. Fe–Pd nanoalloy Mössbauer spectrum is characterized by having a superparamagnetic doublet and a ferromagnetic sextet.     

Magnetic Study of Nanocrystalline Ferrites and the Effect of Swift Heavy Ion Irradiation

100 MeV Si⁺⁷ irradiation induced modifications in the structural and magnetic properties of Mg_0.95Mn_0.05Fe₂O₄ nanoparticles have been studied by using X-ray diffraction, Mössbauer spectroscopy and a SQUID magnetometer. The X-ray diffraction patterns indicate the presence of single-phase cubic spinel structure of the samples. The particle size was estimated from the broadened (311) X-ray diffraction peak using the well-known Scherrer equation. The milling process reduced the average particle size to the nanometer range. After irradiation a slight increase in the particle size was observed. With the room temperature Mössbauer spectroscopy, superparamagnetic relaxation effects were observed in the pristine as well as in the irradiated samples. No appreciable changes were observed in the room temperature Mössbauer spectra after ion irradiation. Mössbauer spectroscopy performed on a 12 h milled pristine sample (6 nm) confirmed the transition to a magnetically ordered state for temperatures less than 140 K. All the samples showed well-defined magnetic ordering at 5 K, whereas, at room temperature they were in a superparamagnetic state. From the magnetization studies performed on the irradiated samples, it was concluded that the saturation magnetization was enhanced. This was explained on the basis of SHI irradiation induced modifications in surface states of the nanoparticles.     

Mössbauer effect phase determination in iron oxide–polyaniline nanocomposites

Mössbauer effect spectroscopy and thermal analysis techniques were applied to characterize polyaniline composites successfully synthesized by embedding Fe oxide nanoparticles (about 10–13 nm) in a polymeric matrix in the presence of dodecyl benzene sulfonic acid and HCl (dopant). Thermal techniques provided quantitative information on iron oxide content and on polyaniline stability and transformations. Mössbauer results indicated that for the whole studied composition range, 3.4 to 100 iron oxide wt.%, composites hold maghemite particles. A preliminary study of the conductivity of the nanocomposites was performed. The largest conductivity was observed for a 8 wt.% maghemite composite where all particles are magnetically unblocked at room temperature within the Mössbauer time window.     

Mössbauer study of iron oxide modified montmorillonite

Montmorillonite particles were modified by iron oxides using the precipitation process with the aim to monitor the differences in the structural and magnetic properties of intercalated and adsorbed Fe³⁺. The Mössbauer spectra recorded at 5 K in zero and 6 T external fields, IR spectra and TG curves measured in zero and 32 mT fields identified the ferrihydrite pillars in an interlayer space of the montmorillonite structure and γ-Fe₂O₃ nanoparticles adsorbed on the mineral surface. The temperature dependent Mössbauer spectra (25–300 K) reflect the superparamagnetic behaviour of maghemite nanoparticles and ferrihydrite pillars with the blocking temperatures of about 80 and 25 K, respectively.     

Magnetic characterization of some nanometric iron oxides

Nanosized magnetite particles embedded in polypyrrole matrix have been studied by Mössbauer and electron magnetic resonance spectroscopy. Comparison with as grown magnetite is made. Hyperfine fields distribution is determined and line shape of resonance curves are discussed in terms of composite structure, sizes and treatments.     

Magnetic and Mössbauer spectroscopic studies of NiZn ferrite nanoparticles synthesized by a combustion method

The properties of nanocrystalline Ni_0.5Zn_0.5Fe₂O₄ synthesized by an auto-combustion method have been investigated by magnetic measurements and Mössbauer spectroscopy. The as-synthesized single phase nanosized ferrite powder is annealed at different temperatures in the range 673–1,273 K to obtain nanoparticles of different sizes. The powders are characterized by powder X-ray diffraction, vibrating sample magnetometer, transmission electron microscopy and Mössbauer spectroscopy. The as-synthesized powder with average particle size of ~9 nm is superparamagnetic. Magnetic transition temperature increases up to 665 K for the nanosized powder as compared to the transition temperature of 548 K for the bulk ferrite. This has been confirmed as due to the abnormal cation distribution, as evidenced from room temperature Mössbauer spectroscopic studies.     

Surface oxidation control of nanosized magnetite and Mössbauer measurements

Selected highly homogeneous powders of Fe₃O₄ with different particle size on the nanometer scale (10?±?2 and 3?±?2 nm) obtained by soft-chemical methods were studied by Mössbauer spectroscopy. The study shows clearly the powerful possibilities of Mössbauer spectroscopy to analyze the surface oxidation of nanostructured powders of magnetite. On the other hand, it is shown that for very small superparamagnetic particles the spectrum of magnetite might be quite similar to that of maghemite, making it difficult to distinguish between both phases.