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Surface and Internal Spin Canting in ??-Fe 2 O 3 Nanoparticles
Abstract
Structural and magnetic properties of γ-Fe2O3 have been studied in isometric nanoparticles ranging from 3 to 14 nm with a narrow particle size distribution. Cation vacancy order is observed for particles larger than 5 nm in diameter giving rise to a cubic superstructure, while for the smallest particles these vacancies are disordered. All magnetic properties measured showed a strong dependence on the average crystallite size. For the ordered samples, saturation magnetization was found to decrease linearly with decreasing crystallite size due to a surface spin canting effect. However, a stronger decrease was observed in the disordered samples, suggesting that also an internal spin canting (cation vacancy order−disorder) has to be taken into account to explain the magnetic properties of nanoparticles. The room-temperature coercive field decreases with decreasing crystallite size; however at low temperatures, the coercivity increases as the size decreases, reaching values larger than 3000 Oe. A model to explain the magnetic properties of these particles considering both surface and order−disorder effects is proposed.
... Nanoparticles have a saturation magnetisation that depends strongly on their size. Due to reduced exchange coupling at the surface, magnetic materials exhibit disordered spin glass-like layers near the surface [30,31]. In bulk magnetic systems, this disordered surface layer is small relative to the system's volume, and therefore surface spin canting effects are negligible. ...
... value for plate-like structure has the highest value for 5 T applied fields. As reported by Kodama and Berkowitz [43], Martinez et al [44], and Morales et al [30], surface spin disorder and the formation of a spin glass-like state can cause this anomalous effect [30,31]. Further, demagnetisation effects related to the morphology of the structure may play a significant role in the determination of magnetic entropy change, with significant variations in spherical, rod-like, and plate-like particles [45][46][47]. ...
... value for plate-like structure has the highest value for 5 T applied fields. As reported by Kodama and Berkowitz [43], Martinez et al [44], and Morales et al [30], surface spin disorder and the formation of a spin glass-like state can cause this anomalous effect [30,31]. Further, demagnetisation effects related to the morphology of the structure may play a significant role in the determination of magnetic entropy change, with significant variations in spherical, rod-like, and plate-like particles [45][46][47]. ...
Single-phase Gd2O3 nanostructures with different morphologies, such as nanoparticles, nanorods, nanospheres, and nanoplates, were synthesised. Gd2O3 1D nanorods and 2D nanoplate architectures were prepared via the hydrothermal method, while 3D hollow nanospheres were synthesised via homogeneous precipitation. The magnetic and magnetocaloric properties of Gd2O3 nanostructured particles were studied as functions of temperature and field. The material demonstrated typical paramagnetic behaviour in the measured temperature range of 3–300 K. The magnetic entropy change (−ΔSM) was determined from the magnetic isotherms measured in the 3–38 K temperature range in the field up to 5 T. The maximum change in magnetic entropy value 11.2 J kg−1 K−1 for the nanoplate, 9.4 J kg−1 K−1 for the nanorod, 9.2 J kg−1 K−1 for the nanosphere, and 10.7 J kg−1 K−1 for the nanoparticle sample was observed at temperature 5 K for the magnetic field of 5 T. Owing to large magnetic entropy value, these Gd2O3 nanostructured particles would be considered promising materials for magnetic refrigeration at cryogenic temperatures.
... As a result, the Ms of small nanoparticles is less than for larger ones. According to [2,8,10,[14][15][16][17], catechols adsorbed on the surface influence the surface structure of MNPs. The reason for the change in the structure of the outer layer is the changed Fe-O bond length. ...
... The saturation magnetization values of pure MNPs ("M s pure") were higher for the functionalized MNPs than for the starting MNPs. The increase in "M s pure" could be due to the minimization of the surface-spin canting [2,8,10,[14][15][16][17] or the reduction of Fe(III) to Fe(II) [12,13], followed by the formation of magnetite on the surface of MNPs. However, the results of this study show that the origin of higher magnetization is the change in size and size distribution of the functionalized MNPs. ...
In this study, MNPs were functionalized with pyrocatechol (CAT), pyrogallol (GAL), caffeic acid (CAF), and nitrodopamine (NDA) at pH 8 and pH 11. The functionalization of the MNPs was successful, except in the case of NDA at pH 11. The thermogravimetric analyses indicated that the surface concentration of the catechols was between 1.5 and 3.6 molecules/nm2. The saturation magnetizations (Ms) of the functionalized MNPs were higher than the starting material. XPS analyses showed only the presence of Fe(III) ions on the surface, thus refuting the idea of the Fe being reduced and magnetite being formed on the surfaces of the MNPs. Density functional theory (DFT) calculations were performed for two modes of adsorption of CAT onto two model surfaces: plain and adsorption via condensation. The total magnetization of both adsorption modes remained the same, indicating that the adsorption of the catechols does not affect the Ms. The analyses of the size and the size distribution showed an increase in the average size of the MNPs during the functionalization process. This increase in the average size of the MNPs and the reduction in the fraction of the smallest (i.e., <10 nm) MNPs explained the increase in the Ms values.
... Maghemite nanoparticles showed typical ferromagnetic characteristics. The lower Ms of maghemite nanoparticles than their bulk may be due to surface spin effects (Morales et al., 1999), as described by other investigators (Jing, 2006;Woo et al., 2004). The magnetic properties of ferromagnetic material were considered to rely on the materials' size, surface, and crystalline nature. ...
Textile dyes have a major issue of the contamination of water and are hazardous to aquatic environments. This work reports the development of an efficient process for iron oxide nanoparticle synthesis by a modified co-precipitation technique. The ultrasonic energy was used to enhance the synthesis of maghemite nanoparticles. A comprehensive study of vital process factors was carried out to develop the optimum conditions for synthesising pure Fe2O3 nanoparticles. The effect of process variables was modelled and analysed with Box–Behnken statistical design and response surface methodology using Design-Expert software. The best outcome with 25-nm size was achieved with optimum processing conditions at a pH level of 12, a temperature of 70 °C, and a time of 60 min. The end products were confirmed with X-ray diffraction. Further, the nanoparticles were characterised with a scanning electron microscope, BET, UV–visible spectrophotometer, and vibrating sample magnetometer. The method described here offers significant advantages over other techniques for the large-scale production of Fe2O3 nanoparticles in a short time compared to other procedures. The prepared maghemite nanoparticles were successfully employed for methylene blue (MB) dye adsorption from water. Further, different adsorption process parameters were examined thoroughly. The data was analysed using Langmuir and Freundlich isotherms, whereas the adsorption kinetics of dye were investigated by employing the pseudo-first- and pseudo-second-order models. Higher values of R² showed better fitness of the experimental data on dye removal to the Freundlich isotherm model and pseudo-second-order kinetic model. The maximum adsorption capacity of maghemite nanoparticles was observed to be 96.52 mg g⁻¹. The adsorbent maghemite nanoparticles can be easily restored and reused. The combination of facile desorption and effective regeneration positions the prepared maghemite nanoparticles as a compelling candidate for industrial wastewater treatment applications.
... It can be seen that at 5 K, the sample CA-4 possesses an H c value notably larger than the other three samples, which consists of larger particles. Such a behaviour can be explained by the fact that as the particle size is decreased, the surface effects become dominant [57], and the surface spin disorder enhances the effective anisotropy constant up to values larger than those reported for the bulk material [58]. ...
Four samples containing magnetic iron oxide nanoparticles (MIONs) of various sizes were prepared employing a simple low temperature method of oxidative precipitation from FeCl2∙4H2O-NaOH-NaNO3 aqueous solution. For preparation of two samples the usual oxidation-precipitation synthesis protocol was modified by using the EDTA chelating agent as a stabilizer of the Fe2+ ions in a solution, which resulted in partial capping of prepared MIONs with EDTA molecules. Three out of four samples were subjected to the citric acid (CA) functionalization in the post synthesis protocol. Structural and magnetic properties of the synthesized MIONs were assessed by various experimental techniques (XRD, TEM, FTIR, DLS, Mössbauer, SQUID). Average size of spherical-like MIONs was tuned from 7 nm to 38 nm by changing the synthesis protocol. Their room temperature (RT) saturation magnetization, Ms, was in the range from 43 to 91 emu/g. Magnetic heating ability, expressed via specific absorption rate (SAR) value which ranged from 139 to 390 W/gFe, was discussed in relation to their structural and magnetic properties and the possible energy dissipation mechanisms involved. The best heating performance was exhibited by the sample decorated with EDTA and having bimodal size distribution with average particle sizes of 14 and 37 nm and Ms = 87 emu/g. Though this sample contained particles prone to form aggregates, capping with EDTA provided good colloidal stability of this sample, thus preserving their magnetic heating ability. It was demonstrated that two samples, consisting of 7 nm-sized CA- or 14 nm-sized EDTA/CA-functionalized superparamagnetic MIONs, having similar hydrodynamic radius, heat in a very similar way in the relatively fast oscillating AC magnetic field, f = 577 kHz.
... Saturation magnetization, Ms of the IONs is 73.6 emu/g. The mean magnetic particle size, dMAG (with standard deviation, σ) was calculated according to the relations (Morales et al. 1999;Karaagac et al. 2010) and found to be 7.8 ± 2.4 nm. After the immobilization, the Ms Value of immobilized β-glucosidase is 56.3 emu.g -1 and the sample is superparamagnetic with a Hc of 3 Oe. ...
This paper reports on novel and efficient enhancement effects of fruit juice aroma using immobilized β-glucosidase, the enzyme involved in important functions in living organisms, onto superparamagnetic nanoparticles Fe3O4 via carbodiimide β-glucosidase was purified from mandarin (Citrus reticulata) using ammonium sulfate precipitation and hydrophobic interaction chromatography. To be used in this study, superparamagnetic nanoparticles were synthesized and then the shape, size, and magnetism properties of the nanoparticles were characterized. The purified enzyme was immobilized on the nanoparticles. The optimum temperature for β-glucosidase (40 ℃) was increased by 10 ℃ after immobilization, while the optimum pH values of free and immobilized β-glucosidase were 5.5. While the Km and Vmax values of the free enzyme were 0.264 mM and 294 EU, immobilized enzyme’s Km and Vmax were 0.222 mM and 370 EU, respectively. In addition, it was determined that the storage stability of the immobilized enzyme was higher than the free enzyme. When the effect of some metal ions on the enzyme activity was examined, it was observed that Fe+2 increased the enzyme activity while other metals inhibited it. According to the results obtained, the immobilized enzyme had a flavor-enhancing effect on mandarin juice.
... On the other hand, in disordered samples where atomic level defects (impurities, vacancies, and dislocations) are present in an MNP. The defects could lead to both surface and internal spin canting [82,83]. ...
Nowadays, magnetic nanoparticles (MNPs) have been extensively used in biomedical fields such as labels for magnetic biosensors, contrast agents in magnetic imaging, carriers for drug/gene delivery, and heating sources for hyperthermia, among others. They are also utilized in various industries, including data and energy storage and heterogeneous catalysis. Each application exploits one or more physicochemical properties of MNPs, including magnetic moments, magnetophoretic forces, nonlinear dynamic magnetic responses, magnetic hysteresis loops, and others. It is generally accepted that the static and dynamic magnetizations of MNPs can vary due to factors such as material composition, crystal structure, defects, size, shape of the MNP, as well as external conditions like the applied magnetic fields, temperature, carrier fluid, and inter-particle interactions (i.e., MNP concentrations). A subtle change in any of these factors leads to different magnetization responses. In order to optimize the MNP design and external conditions for the best performance in different applications, researchers have been striving to model the macroscopic properties of individual MNPs and MNP ensembles. In this review, we summarize several popular mathematical models that have been used to describe, explain, and predict the static and dynamic magnetization responses of MNPs. These models encompass both individual MNPs and MNP ensembles and include the Stoner-Wohlfarth model, Langevin model, zero/non-zero field Brownian and Néel relaxation models, Debye model, empirical Brownian and Néel relaxation models under AC fields, the Landau–Lifshitz–Gilbert (LLG) equation, and the stochastic Langevin equation for coupled Brownian and Néel relaxations, as well as the Fokker–Planck equations for coupled/decoupled Brownian and Néel relaxations. In addition, we provide our peers with the advantages, disadvantages, as well as suitable conditions for each model introduced in this review.
... In the latter, the cation vacancies are absent. The coprecipitation method enables the synthesis of nanoparticles in large amounts but limits the control on particle size distribution [37,38]. ...
A significant portion of the world population has been affected by bone diseases like osteoporosis and bone cancer. A site-specific drug delivery approach can result in safe and effective clinical outcomes in the treatment of these diseases. In this context, the delivery of therapeutic agents using magnetic nanoparticles (MNPs) has been widely investigated over the past few decades. MNPs have attractive properties such as superparamagnetism, which has led to them being widely recognized as a promising tool in biomedical applications, including protein or cell separation, magnetic resonance imaging, and cancer hyperthermia treatment, besides being used as drug delivery vehicles and signal enhancement agents. In addition to the size of MNPs, surface functionalization and coatings are critical parameters that need to be considered for site-specific targeting. In this chapter, we cover the synthesis of magnetic nanoparticles (magnetite and maghemite), their functionalization, characterization, and applications in treating bone diseases.
... Though Maghemite has different preparation methods, the process parameters are very stringent and sensitive to temperature. Usually, α-Fe 2 O 3 can be synthesized using any Fe salts in a single step with or without temperature treatments [17] whereas, γ-Fe 2 O 3 involves multi-step processes which involve more number of chemicals apart from the precursor salt [11,18], usually involving the oxidation of Fe 3 O 4 [16], and oxidation of ferrous hydroxide in ion-exchange polymers [17]. Hence a single-step synthesis process for the large-scale production of γ-Fe 2 O 3 is essential from a commercial point of view. ...
... The effect of spin canting is strictly associated with the presence of structural disorder, therefore low crystallinity, at the surface and/or in the core of the MNPs. In fact, it is due to reduced and modified atomic coordination and the presence of topological defects, resulting in altered super-exchange bonds [59,[65][66][67][68]. The highest M S (~86 emu/g) is measured in C26 MNPs. ...
The paper aims to compare different methods able to estimate the specific loss power (SLP) generated by three different types of magnetic nanoparticles, MNPs, dispersed in a suspension fluid, e.g., octane or water. The nanoparticles were characterized morphologically in terms of shape and size, chemically for composition and their physical properties like magnetization and SLP were studied. We evidenced the differences in SLP evaluation due to the applied method, particularly in the presence of thermally induced phenomena such as aggregation or precipitation of MNPs that can affect the heating curve of the samples. Then, the SLP determination methods less sensible to this phenomenon appear to be the ones that use the initial slope when the sample is in quasi-adiabatic condition. Finally, we propose a comparison of those methods based on the pros and cons of their use for the SLP determination of magnetic nanofluids. In particular, the analysis of the behavior of the heating curve is useful to evaluate the useful amplitude of the interval analysis for the initial slope methods.
... Furthermore, it can be seen that the susceptibility of the SC nanocatalyst is lower than the one of the MC ones due to spin canting effect on the surface because of their small particle size [32]. The superparamagnetic moment resulting from the coupling of the moments of the particles that are in the superparamagnetic regime at a certain temperature increases from SC to MC sample, according to the internal structure of the particles and with previous works [33]. ...
Advanced oxidation processes can counteract the hazardous effects of polluted effluents in a highly efficient way, in many cases limited by the adsorption capacity of the nanocatalyst that depends on their size, internal structure and coating. Here, magnetic iron oxide nanocatalysts consisting on single core (SC), multicore (MC) and core-shell (CS) structures, stabilized with citrate and silica, have been evaluated for the degradation of anionic acid orange 8 (AO8) and cationic methylene blue (MB). It was observed that the adsorption is a limiting parameter, as expected in a mainly heterogeneous process involving molecular adsorption, reaction, and desorption at the catalyst surface. Thus, for the anionic dye, AO8, no degradation is observed by any of the nanocatalysts considering their negative surface charge. However, for MB loaded SC or CS nanocatalysts, highest degradation yields (almost 100% after 180 min at 90 ºC) were achieved through a homogeneous and heterogeneous catalysis in the case of SC and a pure heterogeneous process in the case of CS. MC presents the lager aggregate size due to the lack of coating and low surface charge, leading to poor capacity of adsorption and degradation. On the other hand, magnetic induction heating promotes the degradation of MB (up to ≈50%, respect to room temperature). The results show that iron oxide nanocatalysts through Fenton reactions are an interesting alternative for wastewater treatment considering also that iron is non-toxic and one of the most abundant elements on Earth and can be recovered simply by applying a magnetic field.
... In the maghemite's spinel structure, Iron is located at octahedral sites (Oh) and tetrahedral (Td) sites and generates cationic vacancies. These cationic vacancies inside the octahedral site distinguish it from magnetite [58]. The LaMer diagram depicts the coprecipitation process involving a small burst of nucleation when the species concentration approaches critical supersaturation, followed by steady nuclei development due to solute diffusion to the crystal surface. ...
Ionic liquids (ILs) are getting prominence as eco-sustainable solvents, especially as alternatives to existing mediums in chemical reactions because of the advantage of incredibly low vapor pressure, which makes them simple to preserve in a process. Although there are multiple advantages to adopting ILs, still some restrictions place a cap on their usefulness due to which ILs are supported or immobilized on solid support materials which combine the benefits of ILs (low volatility, high solvent capacity, etc.) with heterogeneous support materials. Magnetic nanoparticle-supported catalytic systems have received much attention due to their extraordinary qualities like ease of availability, large surface-to-volume ratio, chemical inertness, and outstanding thermal stability for the immobilization of ILs. However, due to iron cations in two valence states, Fe²⁺ and Fe³⁺, magnetite Fe3O4 has the most remarkable characteristics in the inverse spinel structure thus, Fe3O4 MNPs have attracted great importance as solid supports for ILs. However, metal nanoparticles accumulate into massive particles and losses the active reaction sites, promoting deactivation, thus coating of nanoparticles is required to prevent irreversible aggregation, for this all Fe3O4 nanoparticles are coated with a homogenous silica layer providing various benefits, such as relatively good media stability and ease of surface functionalization. This review summarizes the applications of immobilized ILs on Fe3O4 MNPs in organic synthesis. Enhanced efficiency can be achieved by mixing desired ionic liquid and nanoparticle into a hybrid nanostructure.
... Also, a band at the 630 cm −1 appeared with little intensity, which confirmed partially oxidized Fe 3 O 4 and the presence of the iron oxide phase's maghemite (γ-Fe 2 O 3 ). [34] The successful conjugation of the FA ligand onto the surface of Fe 3 O 4 @ SiO 2 MNPs can be confirmed by the comparison of IR spectra of γ-Fe 2 O 3 @ SiO 2 -FA MNPs and free FA (Figure 1b). ...
In this investigation, Fe3O4 magnetic nanoparticles (MNPs) were prepared via a chemical coprecipitation reaction, and the surface of Fe3O4 MNPs was coated with silica by a sol-gel process. The surface of Fe3O4@SiO2 MNPs was modified by an antioxidant agent, trans-ferulic acid, to achieve water-soluble MNPs for biological applications. Fourier transform infrared spectroscopy (FT-IR) showed that the MNPs were successfully coated with SiO2 and ferulic acid (FA) ligand. The morphology of γ-Fe2O3@SiO2-FA MNPs was found to be spherical in images of transmission electron microscopy (TEM) and showed a uniform size distribution with an average diameter of 21 nm. The in vitro cytotoxic activity of γ-Fe2O3@SiO2-FA MNPs and FA were investigated against the human cancer cells (MCF-7, PC-3, U-87 MG, A-2780, and A-549) by MTT colorimetric assay. The cytotoxic effect of MNPs on all cancer cell lines was several times of magnitude higher compared to free FA except for A-549 cell lines. Furthermore, in vitro DNA binding studies were investigated by UV-vis and circular dichroism spectroscopies.
... The number of spins on the surface increases as the particle size decreases; thus, the spin canting effect increases. Therefore, the Ms of the nanoparticles is lower than that of the bulk [36][37][38]. As shown, the Ms values of the samples obtained at 15,30,45, and 60 min of carburization are 41. ...
Ni/Ni3C core-shell nanoparticles with an average diameter of approximately 120 nm were carburized via a chemical solution method using triethylene glycol. It was found that over time, the nanoparticles were covered with a thin Ni3C shell measuring approximately 1–4 nm, and each Ni core was composed of poly grains. The saturation magnetization of the core-shell nanopowders decreased in proportion to the amount of Ni3C. The synthesis mechanism of the Ni/Ni3C core-shell nanoparticles was proposed through X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) analyses.
... In the maghemite's spinel structure, Iron is located at octahedral sites (Oh) and tetrahedral (Td) sites and generates cationic vacancies. These cationic vacancies inside the octahedral site distinguish it from magnetite [58]. The LaMer diagram depicts the coprecipitation process involving a small burst of nucleation when the species concentration approaches critical supersaturation, followed by steady nuclei development due to solute diffusion to the crystal surface. ...
... Consequently, they have attributed the above results correlated with nanorods to the size of the particle, were they claimed that the M s is highly related to the size of the particles and generally increases with it, besides; the effect of high anisotropy nanorods restricts them from magnetizing in directions other than their magnetic easy axis [54]. Therefore, they referred the small value of Ms obtained in case of nanorods to several principle reasons: [52,55] Small size and shape anisotropy of the nanorods Surface spin canting Defective organic surface layer Furthermore, concerning the magnetic structure and coercivity, it has been shown through the low-field region that hysteresis loops exist and illustrated the ferromagnetic behaviour of the as-obtained samples and the coercivity (H c ) of nanorods, nanoplates and spherical nanoparticles are respectively 46.53, 53.8 and 35.64 Oe. Additionally, they specified that the considerable reason behind the high coercivity values of nanorods and nanoplates compared to spherical nanoparticles is the notable anisotropic shapes correlated with them, in which the coercivity of magnetic materials mainly depends on the size, shape, and crystalline anisotropy [52,56]. ...
I Thanks First, I want to thank God for all His blessings, the strength he gives me each day, and for all the people around me who make life more meaningful. And I hope in God to keep us safe and to include us in his care and protection and may He bestow all of us the best of this world and hereafter. Unlimited thanks to our Professor Joumana Toufaily, the coordinator of the Master 2 of Research, Physical Chemistry of Materials and Catalysis "M2R CPMC" and the director of the LEADDER Laboratory, thanks are the least I can say to her to show my appreciation for everything she has done, she has the capacity to translate vision into reality, to choose the harder right rather than the easier wrong, whatever happens, she was there to play her thoughtful part. Thanks for her kindness which can never be repaid and for her understanding and the difference it made. My thanks continued to the director of the (MCEMA) laboratory and our honourable professor, Dean Tayssir Hamieh, who inspires hope, ignite the imagination, and instill a passion for learning. Attending his classes was always like taking a deep dive into an ocean full of knowledge and wisdom, he was the best teacher and scientific beacon ever. It gives me great pleasure to extend thanks from the bottom of my heart to the director of my internship Doctor Mohamad Hamieh, the partner of success, that expressing thanks seems a hard task for me, and it is difficult to find words to precise my gratitude towards him, despite his own work pressures, he took out the time to help me out, I totally appreciate it. Thanks for his unlimited giving, support, and for being such an inspiration to me. My gratitude also goes to the jury members, Doctor Nabil Tabaja and Doctor Houssam Obeid for kindly checking and evaluating this work. I thank them heartily. Finally, I thank my supportive and caring family, the treasure greater than anything I can imagine, for their endless love and my soul-nourishing that have made the hard times so much easier. II Abstract Spherical iron oxide-based magnetic nanoparticles have been in the focus of research due to their high chemical stability, biocompatibility, and superparamagnetic properties, in which the main breakthroughs in the application of these magnetic nanostructured systems are their clinical use, such as magnetic resonance imaging (MRI), magnetic drug delivery, magnetic hyperthermia, and separating agents in magnetic separation techniques. However, improving the magnetic behaviour and biological activity by controlling the morphology of iron oxide nanoparticles has become an obsessive thought, where many efforts have been made to develop synthetic routes that produce different anisotropic shapes. Accordingly, the hydrothermal/solvothermal synthetic chemical route was adopted to produce magnetite (Fe 3 O 4) nanorods in the appropriate size because it enables good control of size and shape, contributing to a better degree of crystallinity and water solubility of the products. Furthermore, it has been shown that by adjusting the shape of magnetite iron oxide to a rod-like morphology with a length of 30-70 nm and a diameter of 4-12 nm, an effective contrast agent for magnetic resonance imaging (MRI) with high relaxation capability R2 was realized. The reason for the increased contrast of the nanorods in MRI is the nanorods' larger surface area and anisotropic morphology. In which the magnetic field induced by the rod was stronger than the spherical one of equivalent material volume, wherefore, a stronger magnetic field in a large volume leads to a higher R2 relaxation in the case of the nanorod, thus a shape tuning of these iron oxides holds a great promise for highly sensitive, early-stage and accurate detection in the clinic. III
... XRD technique was used to analyze the crystalline structure of Fe 3 O 4, Fe 3 O 4 @SiO 2 MNPs, and c-Fe 2 O 3 @SiO 2 -CGA MNPs. Figure 1 The IR spectrum corresponding to c-Fe 2 O 3 @SiO 2 -CGA MNPs showed a peak at 582 cm À1 related to the Fe-O vibrations of Fe 3 O 4 core and a peak at the 637 cm À1 confirming partially oxidized Fe 3 O 4 and the existence of iron oxide phase in maghemite (c-Fe 2 O 3 ) (Figure 2(a)) (Morales et al., 1999). ...
In this study, nanoparticles with both anticancer and antibacterial features were synthesized through loading chlorogenic acid (CGA) of essential oils on magnetic nanoparticles (MNPs). Characterization of γ-Fe2O3@SiO2-CGA MNPs was performed using Fourier transform infrared (FT-IR) spectroscopy and transmission electron microscopy (TEM) that show effective coating of the MNPs with SiO2 and CGA ligand and spherical shape of the nanoparticles with a mean diameter of 16 nm, respectively. The cytotoxicity study demonstrated that γ-Fe2O3@SiO2-CGA MNPs had fewer toxic effects on normal cells (Huvec) than on cancerous cells (U-87 MG, A-2780 and A-549), and could be a new potential candidate for use in biological and pharmaceutical applications. The interaction of calf thymus deoxyribonucleic acid (ct-DNA) with γ-Fe2O3@SiO2-CGA MNPs indicated that the anticancer activity might be associated with the DNA binding properties of γ-Fe2O3@SiO2-CGA MNPs. Moreover, the interaction of γ-Fe2O3@SiO2-CGA MNPs with human serum albumin (HSA) suggests that the native conformation of HSA was preserved at the level of secondary structure, indicating that the γ-Fe2O3@SiO2-CGA MNPs do not show any cytotoxicity effect when they are injected into the blood. Antibacterial tests were performed and represented γ-Fe2O3@SiO2-CGA MNPs attained better antibacterial function than CGA as free.
... If iron cations are randomly distributed on the octahedral sites, then c-Fe 2 O 3 possesses the structure just like Fe 3 O 4 belonging to space group Fd3m. The vacancies can be ordered, giving rise to either cubic symmetry or tetragonal symmetry [40,41]. According to Braun [18] [12]. ...
In various biomedical applications of iron oxide nanostructures, superparamagnetic nanoneedles offer benefits to access the interior of cells without damage. However, use of superparamagnetic nanoneedles should not be limited to biomedical applications. To explore and extend the field of application, this study is focused on detailed investigation of structural, magnetic, and field emission behavior of iron oxide. Iron oxide nanoneedles are prepared using template-free oleic acid-assisted sol–gel method by varying sols’ molarity in the range 0.2–2.0 mM (interval 0.2 mM). Formation of nanoneedles with fine tips and diameter of 20, 23, and 25 nm and length of 700 nm, 1.0 μm, and 1.2 μm at 0.2, 1.0, and 2.0 mM sols are confirmed using Scanning Electron Microscopy. While for rest of the molarity range studied diameter of nanoneedles increases to ~ 50 nm. At 0.2 mM sol magnetite (Fe3O4) phase is observed and vacancy ordered and disordered maghemite (γ-Fe2O3) phases are observed at 0.8–1.0 and 1.4–2.0 mM sols, respectively. Formation of these phases of iron oxide with variation in sols’ molarity is also confirmed using FTIR spectra and Raman spectroscopy. Iron oxide nanoneedles show soft magnetic behavior with high saturation magnetization of 73.2, 43.43, and 75.18 emu/g at 0.2, 1.0, and 2.0 mM sols, respectively. These magnetic nanoneedles have potential applications in cell probing. Furthermore, nanoneedles are also tested for their field emission properties. It is observed that nanoneedles, with disordered maghemite phase, synthesized using 2.0 mM sol have high field emission properties along with low turn-on field of 3.77 Vμm⁻¹. Thus, this study reveals ordered and disordered phases of iron oxide using single route. Furthermore, these phases can be utilized for different applications, such as Fe3O4 (at 0.2 mM) phase for biomedical applications and γ-Fe2O3 phase as field emitters.
The identification of metastasis “seeds,” isolated tumor cells (ITCs), is of paramount importance for the prognosis and tailored treatment of metastatic diseases. The conventional approach to clinical ITCs diagnosis through invasive biopsies is encumbered by the inherent risks of overdiagnosis and overtreatment. This underscores the pressing need for noninvasive ITCs detection methods that provide histopathological‐level insights. Recent advancements in ultra‐high‐field (UHF) magnetic resonance imaging (MRI) have ignited hope for the revelation of minute lesions, including the elusive ITCs. Nevertheless, currently available MRI contrast agents are susceptible to magnetization‐induced strong T2‐decaying effects under UHF conditions, which compromises T1 MRI capability and further impedes the precise imaging of small lesions. Herein, this study reports a structural defect‐enabled magnetic neutrality nanoprobe (MNN) distinguished by its paramagnetic properties featuring an exceptionally low magnetic susceptibility through atomic modulation, rendering it almost nonmagnetic. This unique characteristic effectively mitigates T2‐decaying effect while concurrently enhancing UHF T1 contrast. Under 9 T MRI, the MNN demonstrates an unprecedentedly low r2/r1 value (≈1.06), enabling noninvasive visualization of ITCs with an exceptional detection threshold of ≈0.16 mm. These high‐performance MNNs unveil the domain of hitherto undetectable minute lesions, representing a significant advancement in UHF‐MRI for diagnostic purposes and fostering comprehensive metastasis research.
This paper explores the intricate interplay between inorganic nanoparticles and Earth's biochemical history, with a focus on their electron transfer properties. It reveals how iron oxide and sulfide nanoparticles, as examples of inorganic nanoparticles, exhibit oxidoreductase activity similar to proteins. Termed "life fossil oxidoreductases", these inorganic enzymes influence redox reactions, detoxification processes, and nutrient cycling in early Earth environments. By emphasizing the structural configuration of nanoparticles and their electron conformation, including oxygen defects and metal vacancies, especially electron hopping, the paper provides a foundation for understanding inorganic enzyme mechanisms. This approach, rooted in physics, underscores that life's origin and evolution are governed by electron transfer principles within the framework of chemical equilibrium. Today, these nanoparticles serve as vital biocatalysts in natural ecosystems, participating in critical reactions for ecosystem health. The research highlights their enduring impact on Earth's history, shaping ecosystems and interacting with protein metal centers through shared electron transfer dynamics, offering insights into early life processes and adaptations.
We’ll concentrate on the diagnostic aspect in this chapter. Figure 8.1 presents the topics focused on in this chapter hierarchically. Since a long time ago, iron oxide nanoparticles (IONP) with distinctive magnetic characteristics and great biocompatibility have been employed extensively as MRI contrast agents (CA).
In this study, cadmium and chromium doped cobalt ferrite nanoparticles (Co1-xCdxFe2-xCrxO4) (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) were synthesized by hydrothermal method. Then, using X-ray diffraction (XRD), scanning electron microscopy (FESEM), Fourier transforms infrared (FTIR) and Raman spectroscopy, structural properties were investigated. XRD analyses show a single-phase spinel structure for annealed samples at 700 °C. The crystallite sizes decrease slightly by increasing Cd and Cr doping from 58 to 53 nm, in agreement with FESEM micrographs. The lattice parameter value was between 8.396 and 8.514 Å. The Raman spectroscopy analysis showed that Co1-xCdxFe2-xCrxO4 nanoparticles have a mixed spinel structure. Then, by using the vibrating sample magnetometer (VSM), we obtained the magnetic parameters of the samples. The maximum saturation magnetization of 76 emu/g and the maximum coercivity field of 1.125 KOe were obtained in the samples of x = 0 and x = 0.1, respectively.
Different types of contaminants are released to wastewater with the rapid
increase in industrial activities, such as heavy metal ions, organics, and hazard organ�isms which are serious harmful to human health. Heavy metal ions, like Pb2+, Cd2+,
Zn2+, and Hg2+ can cause severe health problems in animals and human for its
highly toxic nature. The use of agricultural by-products has been widely investi�gated as an efficient alternative for current costly methods of removing heavy metals
from wastewater. Chemical composition of Rice Straw contains cellulose (32–47%),
hemicellulose (19–27%) and lignin (5–24%). Rice Straw has several characteristics
to predict the functional groups on the surface of the biomass that make it a potential
adsorbent with binding sites capable of taking up metals from aqueous solutions. In
our study, the active sites of Rice Straw were modified using CoFe2O4 nanoparticles
which cause increasing their metal-binding capacity. Adsorption experiments were
carried out using modified Rice Straw to absorb some heavy metals ions like Fe3+,
Mn2+, Cu2+, Cd2+, Zn2+, Ni2+ and Pb2+ from aqueous solution. The prepared samples
were characterized using different analytical techniques. Our results of adsorption
indicated that Rice Straw treated with CoFe2O4 spinel ferrite nanoparticles appeared
to be more efficient to remove heavy metal ions from wastewater
Methods for the synthesis of iron oxide nanoparticles with various modifications (magnetite, maghemite, hematite) and iron-containing nanoparticles with perovskite structure are considered. Particular attention is paid to the method based on the use of microwave radiation, as the most efficient, low-energy method, resulting in the preparation of nanoparticles with a narrow size distribution and a small particle size.
In the present study, by employing ethylenediaminetetraacetic acid (EDTA), tetraethylene pentaamine (TEPA), and rhodamine B (Rb), we designed and synthesized a magnetic adsorbent (Fe3O4@EDTA@TEPA@Rb) on the basis of reversible charge change of Rb and applied to capture phosphopeptides. Rb existing in open planarized zwitterion form when stimulated by acidic loading buffer adsorbs negative phosphopeptides via electrostatic interaction. Under the stimulation of alkalic eluent, ring-closed structure of Rb is formed to elute the enriched phosphopeptides. TEPA containing rich amino groups is used as a crosslinking agent, which is also protonated in acidic loading buffer to bond phosphopeptides. Then phosphopeptides are eluted when TEPA deprotonates in alkalic eluent. Coupled with matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF-MS) detection, phosphopeptide signals originated from 0.4 fmol/μL β-casein digests were successfully detected. In addition, Fe3O4@EDTA@TEPA@Rb can also efficiently enrich phosphopeptides from skimmed milk, human serum and saliva samples (26, 4, 39 phosphopeptides, respectively), opening a new gallery for phosphopeptides-related analysis. In general, the developed adsorbent has the great potential for further application in the near future.
Magnetic properties of superparamagnetic iron oxide nanoparticles are controlled mainly by their particle size and by their particle size distribution. Magnetic properties of multi-core iron oxide nanoparticles, often called iron oxide nanoflowers (IONFs), are additionally affected by the interaction of magnetic moments between neighboring cores. The knowledge about the hierarchical structure of IONFs is therefore essential for understanding the magnetic properties of IONFs. In this contribution, the architecture of multi-core IONFs was investigated using correlative multiscale transmission electron microscopy (TEM), X-ray diffraction and dynamic light scattering. The multiscale TEM measurements comprised low-resolution and high-resolution imaging as well as geometric phase analysis. The IONFs contained maghemite with the average chemical composition [Formula: see text]-Fe[Formula: see text]O[Formula: see text]. The metallic vacancies located on the octahedral lattice sites of the spinel ferrite structure were partially ordered. Individual IONFs consisted of several cores showing frequently a specific crystallographic orientation relationship between direct neighbors. This oriented attachment may facilitate the magnetic alignment within the cores. Individual cores were composed of partially coherent nanocrystals having almost the same crystallographic orientation. The sizes of individual constituents revealed by the microstructure analysis were correlated with the magnetic particle sizes that were obtained from fitting the measured magnetization curve by the Langevin function.
The unique low temperature synthesis of zinc pyrovanadate from oxides was proposed. Zn3V2O7(OH)2·2(H2O) was synthesized by ultrasonic (US) method using ZnO and V2O5 as raw materials. It was established using SEM and TEM methods that Zn3V2O7(OH)2·2(H2O) has the structure of nanosheets. The DTA method and XRD analysis showed the formation of the Zn3V2O8 phase after the removal of crystallization water from Zn3V2O7(OH)2·2(H2O). Ultrasonic treatment of oxides as initial reagents allows obtaining Zn3V2O8 with the specific surface area of 14 m2/g. For comparison, Zn3V2O8 was synthesized by solid-state (SS) synthesis from oxides. The properties of zinc pyrovanadate obtained by US synthesis and conventional SS synthesis were compared. The advantages of US method over conventional SS synthesis were noted.KeywordsZinc pyrovanadateZn3V2O8Ultrasonic synthesisNanostructures
The electrical properties of systems based on polyethylene oxide (PEO), carbon nanotubes (CNTs), and organoclays were studied using the methods of X-ray diffraction analysis, optical microscopy, and impedance spectroscopy. It is established that the introduction of nanofillers into the PEO matrix leads to a significant reduction in its degree of crystallinity. For systems filled with CNTs, a percolation transition is observed, which was analyzed in the framework of the scaling approach. It was found that the structure of composites that contain organoclays significantly depends on their type. For systems containing montmorillonite, the process of intercalation is observed, and for systems filled with laponite, there is exfoliation of organoclay. It is shown that when organomodified laponite (OLP) is introduced into the system, the percolation threshold is shifted to the region of lower CNT concentrations. At the same time, loosening of aggregates from CNT is observed. Modeling of impedance spectra for systems based on PEO by the method of equivalent circuits is carried out. It is established that the introduction of OLP more than 0.4% into the system leads to a significant reduction in electrical conductivity. This effect is explained by the fact that the OLP plates form their own network and prevent the formation of direct contacts between nanotubes.KeywordsPolymer nanocompositesCarbon nanotubesOrganoclayPercolationElectrical conductivity
Hybrid magnetic particles based on Laponite® (Lap) (Rockwood Additives Ltd., UK) and nanomagnetic (NM) particles have been synthesized. The NM was synthesized using the Elmore method. For preparation of LapM hybrids, the Lap and NM were mixed in aqueous suspensions at pH 7.3 and T = 298 K. The concentration of NM particles at suspensions was fixed at 0.75 wt%, and concentration of Lap was varied in the range of 0.0375–1.5 wt% (the mass ratio Xm = mNM/mLap was varied within the range 20.0–0.5). The Lap, LapM, and NM particles were characterized using FTIR-spectroscopy, X-ray diffraction, magnetic susceptometry, transmission electron microscopy, measurements of particle size distribution function, and electrophoretic mobility. The observed variations in magnetic susceptibility χ, ζ-potential and overcharging were explained by the deep integration between Lap and NM particles, and interplaying between hydrophobic and electrostatic interactions in LapM hybrids.KeywordsLaponite®PlateletMagnetic hybrid nanoparticlesElectrosurface properties
Cellulose was extracted from mango fibers and subjected to acid hydrolysis to obtain a nanofiber. Two morphological structures based on the polylactic acid (PLA)/nanocellulose (NC) combination have been synthesized and Fe3O4 NPs (M) are incorporated into both combinations. The first formulation is obtained by blending technique (PLA/M-NC) and the second formulation is obtained by self-assembly of grafted copolymer (M-PLA-co-NC). The magnetic nanocomposites are used as carriers for 5-fluorouracil (5-FU), an anti-cancer drug, and curcumin (CUR) to get PLA/M-NC/5-FU/CUR and M-PLA-co-NC/5-FU/CUR. The structural, morphological, and magnetic properties of the obtained nanocomposites were characterized by various techniques. The loading, release of 5-FU/CUR and the inhibition efficacy of nanocarriers loaded drugs against bacteria, HePG-2, MCF-7, and HCT-116 cell lines were studied. The two morphological forms of nanocarriers are considered close in loading % of 5-FU; however, the M-PLA-co-NC nanocarrier loaded double the loading % of CUR into PLA/M-NC nanocarrier, revealing superiority of copolymeric micelle than the blended formulation. The dual drugs loaded magnetic copolymeric micelles M-PLA-co-NC/5-FU/CUR revealed slower release, higher antibacterial and antitumor efficacy than the PLA/M-NC/5-FU/CUR. In this respect, the M-PLA-co-NC/5-FU/CUR could be considered a good nanomedicine against Streptococcus, Bacillus subtilis, Klebsiella pneumonia and Escherichia coli bacteria, besides the investigated cell lines.
Miniaturizing metallic materials from the nanoscale to the atomic scale transforms the structures and physical properties. Among these sub-nanoscale materials, some catalysts exhibit activity superior to conventional nanoparticle catalysts. Furthermore, some subnanoparticles become superatoms that exhibit unusual physical properties that deviate from the properties of the original elements. However, conventional metallurgy and chemistry often do not apply to synthetic strategies, structural analysis, and functional design of materials because crystal structures disappear at the sub-nanoscale. This review focuses on the synthesis, structural analysis, and functionality at the sub-nanoscale, overviewing a series of materials research, so-called “atom hybridization,” in which atoms are hybridized to create desired materials for their applications.
In this study the iron oxide incorporated gelatin nanoparticles (IOIGNPS) were prepared following an emulsion crosslinking method employing genipin as a non-toxic crosslinking agent. The drug loaded nanoparticles were characterised by analytical techniques. Whereas the FTIR spectra confirmed the crosslinking of gelatin by genipin and encapsulation of the drug, the TEM analysis revealed the nanosize (up to 100 nm) of the nanoparticles. The magnetisation study suggested for the superparamagnetic nature of nanoparticles. It was found that the amount of released drug increases with increasing percent loading of 5-FU in the range 21.1% to 44.4%. The release profiles of drug were affected by various experimental factors such as the amount and type of gelatin in the feed mixture, pH of the release media, nature of the release medium, and strength of the applied magnetic field. The swelling results indicated that the extent of swelling regulated the extent of drug release.
In this work, we conducted a proof-of-concept experiment based on biofunctionalized magneto-plasmonic nanoparticles (MPNs) and magneto-optical Faraday effect for in vitro Alzheimer's disease (AD) assay. The biofunctionalized γ-Fe2O3@Au MPNs of which the surfaces are modified with the antibody of Tau protein (anti-τ). As anti-τ reacts with Tau protein, biofunctionalized MPNs aggregate to form magnetic clusters which will hence induce the change of the reagent's Faraday rotation angle. The result showed that the γ-Fe2O3@Au core-shell MPNs can enhance the Faraday rotation with respect to the raw γ-Fe2O3 nanoparticles. Because of their magneto-optical enhancement effect, biofunctionalized γ-Fe2O3@Au MPNs effectively improve the detection sensitivity. The detection limit of Tau protein as low as 9 pg/mL (9 ppt) was achieved. Furthermore, the measurements of the clinical samples from AD patients agreed with the CDR evaluated by the neurologist. The results suggest that our method has potential for disease assay applications.
This paper reports a simple method of designing and synthesizing magnetic iron oxide (IO) integrated locust bean gum-cl-polyacrylonitrile hydrogel nanocomposites (LBG-cl-PAN/IONP) by in situ mineralization of iron ions in a hydrogel matrix. A two-step gel crosslink method followed by co-precipitation method was used to prepare these novel hydrogels embedded with magnetic iron oxide nanoparticles. The LBG-cl-PAN/IONP hydrogel nanocomposite (HNC) were tested in batch adsorption experiments for their ability to remove a cationic dyes, methylene blue (MB) & Methyl violet (MV), from aqueous solution. In order to analyze the LBG-cl-PAN/IONP HNC, FTIR, XRD, XPS, VSM, TEM, and EDX techniques were applied. Numerous operating parameters were studied, including the amount of adsorbent, the contact time, pH, temperature, the dye concentration, and the coexisting ion concentration. According to the Langmuir isotherm model, MB and MV had maximum monolayer adsorptive capacities of 1250 and 1111 mg/g, respectively. LBG-cl-PAN/IONP HNC controlled IONP oxidation as well as sustained adsorptive removal over a wide pH range (7–10). The key mechanism of adsorption consisted of electrostatic interaction and ion exchange. For successful use in successive cycles after regeneration using HNO3 as eluent, the LBG-cl-PAN/IONP HNC can easily be reused. As a material, the LBG-cl-PAN/IONP HNC is a promising sorbent or composite material for removing toxic dyes from water, and therefore can be applied to enhance water and wastewater treatment technology. Additionally, we have briefly evaluated LBG-cl-PAN/IONP HNC for antibacterial and supercapacitor applications. According to our knowledge, this is the first report describing the use of LBG-cl-PAN/IONP HNC as an excellent sorbent, antibacterial and electrochemical supercapacitor applications.
Doping Mn (II) ions into iron oxide (IO) as manganese ferrite (MnIO) has been proved to be an effective strategy to improve T1 relaxivity of IO nanoparticle in recent years; however, the high T2 relaxivity of MnIO nanoparticle hampers its T1 contrast efficiency and remains a hurdle when developing contrast agent for early and accurate diagnosis. Herein, we engineered the interfacial structure of IO nanoparticle coated with manganese ferrite shell ([email protected]) with tunable thicknesses. The Mn-doped shell significantly improve the T1 contrast of IO nanoparticle, especially with the thickness of ∼ 0.8 nm. Compared to pristine IO nanoparticle, [email protected] nanoparticle with thickness of ∼ 0.8 nm exhibits nearly 2 times higher T1 relaxivity of 9.1 mM⁻¹s⁻¹ at 3 T magnetic field. Moreover, exclusive engineering the interfacial structure significantly lower the T2 enhancing effect caused by doped Mn (II) ions, which further limits the impairing of increased T2 relaxivity to T1 contrast imaging. [email protected] nanoparticles with different shell thicknesses reveal comparable T1 relaxation rates but obvious lower T2 relaxivities and r2/r1 ratios to MnIO nanoparticles with similar sizes. The desirable T1 contrast endows [email protected] nanoparticle to provide sufficient signal difference between normal and tumor tissue in vivo. This work provides a detailed instance of interfacial engineering to improve IO-based T1 contrast and a new guidance for designing effective high-performance T1 contrast agent for early cancer diagnosis.
Wastewater may be defined as a combination of liquid or water-carried waste removed from residences, institutions, and commercial and industrial establishments, together with ground water, surface water and storms. Water is essential for human survival and well-being, so ensuring adequate water resources is critical. However, it has been recorded that more than 80 countries around the world are experiencing extreme water shortages, with approximately 25% of the population lacking adequate access to fresh water in sufficient quantity and quality. Owing to population growth, rapid industrialization, and long-term droughts, the spread of a wide variety of pollutants in surface water and groundwater has become a critical problem worldwide. Controlling the harmful effects of pollution and improving human living conditions are thus important. Heavy metals, inorganic chemicals, organic contaminants, and a variety of other complex compounds persist in wastewater.
Theranostic nanoagents possess the potential to greatly enhance diagnosis and treatment of disease, as they provide for the incorporation of multiple functionalities such as targeting, imaging, and therapy within a single nanoscaffold. Theranostics has a major role in diseases, such as rheumatoid arthritis, cancer, infection, and cardiac disorders, which need personalized methods for treatment and monitoring. This personalized approach prevents the adverse effects associated with drugs, such as those at a high dosage that may lead to drug resistance, relapse, and incomplete remission. The chapter reports the role of theranostic nanoagents for various diseases.
In this study, 0.02 and 0.04 wt % of chitosan (CS) was successfully incorporated in a fixed amount of polyvinylpyrrolidone (PVP)-doped Bi 2 O 3 nanostructures (NSs) via co-precipitation 2 approach. The purpose of this research was to degrade hazardous methylene blue dye and assess antimicrobial potential of prepared CS/PVP-doped Bi 2 O 3 nanostructures. In addition, optical characteristics, charge recombination rate, elemental composition, phase formation, surface morphology, functional groups, d-spacing, and crystallinity of obtained nanostructures were investigated. CS/PVP-doped Bi 2 O 3 nanostructures exhibited efficient catalytic activity (measured as 99%) in neutral medium for dopant-free nanostructures while the inhibition zone was measured using Vernier caliper against pathogens Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) at low and high dose to check antimicrobial activity. Strong bactericidal action was recorded against S. aureus bacteria such that significant inhibition zone was measured at 3.09 mm.
The magnetization of CoFe2O4 nanoparticles is often less than the bulk value of 3.6μB (86 emu/g), corresponding to an inverse distribution of cations in the spinel structure. This paper investigated the Cd doping on cobalt ferrite nanoparticles' structural and magnetic properties. Cobalt ferrite nanoparticles doped with cadmium (Co1-xCdxFe2O4, x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) were prepared by using hydrothermal method. X-ray diffraction (XRD) analysis confirmed cubic spinel structure, and the crystallite size is estimated at around 56–59 nm. Micrographs obtained by scanning electron microscopy (SEM) showed an average particle size of about 60 nm, which is in agreement with the XRD analysis. The absorption band ν1 for samples obtained from the infrared spectrum (FTIR) varies from 586 up to 570 Cm-1 by Cd doping, indicating Cd's replacement on the tetrahedral site. Magnetization values of 71 and 81 emu/g are obtained for x = 0 and x = 0.1 samples, respectively. But the magnetization decreased as the amount of Cd doping further increased due to the decreasing superexchange interaction between tetrahedral and octahedral sites. The rearrangement of Fe3+ and Co2+ cations on tetrahedral and octahedral sites and spin disorder at the surface of nanoparticles can reduce the magnetization below the bulk value. The coercivity field (Hc) value of 1.1 kOe is obtained for the x = 0, and the Hc values decrease with Cd doping. This is due to the decreasing magnetocrystalline anisotropy by substituting cobalt with cadmium.
Metal‐based nanoparticles, especially gadolinium, manganese, and iron, have gained ground in the research of magnetic resonance imaging (MRI) contrast agents. Over the years, contrast agents based on these paramagnetic and superparamagnetic nanomaterials have merited keen attention in the biomedical field due to their desired properties such as sizeable magnetic susceptibility, tunable size, easy surface functionalization, low toxicity, etc. Gadolinium‐based chelates are the traditional MRI contrast agents in the clinic but require improved relaxivities and pharmacokinetics. Nanoparticles possess a larger surface area, demonstrate a longer retention time in the body, and allow the conjugation of several functional molecules to enhance tumor targeting, making them more advantageous. The pursuit of clinically acceptable MRI contrast agents has generated diverse nanoparticles which have augmented their properties, performance, and relevance. Yet, most nanoparticles have not headed for the clinic for various reasons. Here, metal‐based MRI contrast agents and their contrast mechanisms are briefly described. According to relaxation times, T1 and T2, the different types that have evolved are reviewed, emphasizing the properties that have improved their function as MRI contrast agents. Finally, pertinent issues restraining their clinical translation and potential measures to develop more effective and clinically relevant MRI contrast agents are discussed. Nanoparticles based on gadolinium, manganese, and iron have dominated the research of MRI contrast agents due to their desirable characteristics. Despite the significant advances, most nanoparticles are still preclinical, with gadolinium chelates dominating the clinic. This review discusses their major classes highlighting their enriched contrast properties, predicaments, and corrective steps toward clinical translation.
L’utilisation des nanoparticules d’oxyde de fer dans la nanomédecine connaît de grands progrès et devrait permettre d’améliorer la détection précoce et le traitement de nombreuses pathologies, en particulier pour l’oncologie qui constitue un enjeu majeur de santé publique. En effet, la lutte contre le cancer est aujourd’hui élevée au rang de cause nationale pour remplacer les principales voies thérapeutiques qui sont la chirurgie, la radiothérapie et la chimiothérapie. Dans le cadre de cette thèse, nous nous sommes intéressés au volet diagnostic en développant des procédés de synthèse de ces nanoparticules, à savoir la coprecipitation et la décomposition thermique, permettant d'améliorer significativement les propriétés structurales et magnétiques de la ferrite, d'abord, en les substituant par des éléments alcalino-terreux et biocompatibles, ensuite, en synthétisant des nanoparticules en core-shell et enfin en fonctionnalisant leurs surfaces pour qu'elles s'intègrent efficacement dans l'organisme.
Self-assembled α-Fe2O3-GO nanocomposites (NCs) obtained via rapid, easy and economic microwave–assisted method through the carbonization of sugar in presence of ferric nitrate in different concentrations are envisaged for physical properties followed magnetic and ammonia (NH3) sensing measurements. The α-Fe2O3-GO NCs are composed of uniformly distributed spherical particles of ∼20 nm in sizes. The effect of varying magnetic field on the surface and structure of the α-Fe2O3-GO NCs has also been investigated. Composites endow a better magnetization of ∼5.29 emu/g over pristine once. The highest gas response obtained at 100 ppm NH3 concentration at room-temperature (25 °C) for pristine GO is limited to 8%. Attributed to p-n hetero-junction effect and electron spill-over effect on the α-Fe2O3 doping the gas response is greatly improved to 80% at room-temperature. Mechanism for the enhanced sensitivity has carefully been addressed. Gas sensing activities of α-Fe2O3-GO NCs against various target gases are examined using computer assisted Keithley 6514 electro-source meter. Along with physical properties, magnetic and NH3 gas sensor performances of the α-Fe2O3-GO NCs are measured and reported in-depth.
Iron oxide nanoparticles find many applications due to their response when subjected to externally applied magnetic fields. Equilibrium magnetization measurements (commonly known as magnetization curves) are an essential characterization tool to evaluate if particles display hysteresis, and to obtain magnetic properties such as the saturation magnetization. For superparamagnetic particles, one can obtain a magnetic size distribution by fitting the data to a theoretical model, such as the Langevin function, in what is called magnetogranulometric analysis. If one wishes to use the resulting size estimates as a predictor of particle performance in applications, magnetization data must be obtained under conditions that capture the response of the particles with minimal artifacts. In this paper, we used selected iron oxide nanoparticle batches with physical size ranging from 20-45 nm to demonstrate the influence of sample preparation methods on the magnetization data obtained. We show that measurements in powder form and in liquid solvents display varying degrees of particle interaction artifacts at low fields, depending strongly on particle size and on the thickness of the surface coating. In addition, measurements in ‘solid’ waxy hydrocarbon matrices are shown to be susceptible to particle rotation artifacts for large particle sizes. Hard crosslinked polymer matrices are shown to restrict particle motion completely, resulting in magnetization data that follows the Langevin function if the measurement is performed above the blocking temperature of the particles. We end with a discussion of how the presence of matrix-dependent measurement artifacts influence the magnetic diameter fits obtained using magnetogranulometry, and how measuring above and below the blocking temperature can affect fit results.
Maghemite (γ-Fe2O3) has attracted much attention due to its variety of applications in many areas. However, the current preparation methods of γ-Fe2O3 still involve complicated processes and a high cost, thereby needing improvement. In this study, a novel and facile one-step solid-state method for the preparation of γ-Fe2O3 nanoparticles (NPs) is performed through the thermal decomposition of ferric nitrate (Fe(NO3)3⋅9H2O) and the addition of aromatic acids. Three aromatic acids that have different numbers of carboxyl groups (i.e., benzoic acid, phthalic acid, and trimesic acid) are used as additives and their effects on the formation of γ-Fe2O3 NPs are investigated. Furthermore, the influence of the aromatic acid/Fe(NO3)3⋅9H2O mass ratio and calcination temperature on the structural properties of the products are investigated. The structural properties, morphology, and magnetic properties of the products are analyzed through X-ray diffraction, transmission electron microscopy, scanning electron microscopy, nitrogen adsorption/desorption measurements, and magnetic measurements. The results show that the addition of aromatic acids to Fe(NO3)3⋅9H2O leads to the formation of γ-Fe2O3 NPs, and has a significant influence on the morphology of γ-Fe2O3 NPs. When the aromatic acid/Fe(NO3)3⋅9H2O mass ratio is greater than 0.5, the addition of the three aromatic acids leads to the formation of pure γ-Fe2O3. The γ-Fe2O3 NPs obtained from benzoic acid/Fe(NO3)3⋅9H2O and phthalic acid/Fe(NO3)3⋅9H2O systems do not show a well-defined morphology. In contrast, the γ-Fe2O3 NPs obtained from the trimesic acid/Fe(NO3)3⋅9H2O system are composed of a porous three-dimensional hierarchical structure and have the largest Brunauer−Emmett−Teller surface area (100.0 m² g⁻¹).
Mössbauer-effect measurements on extremely small (~60 Å) crystallites of gamma-Fe2O3 show that the spin configuration differs from the Néel type found in large crystallites. It is proposed that the ions in the surface layer are inclined at various angles to the direction of the net moment.
Nanocrystalline maghemite, {gamma}{endash}Fe{sub 2}O{sub 3}, can be synthesized in a microwave plasma using FeCl{sub 3} or Fe{sub 3}(CO){sub 12} as the precursor. Electron microscopy revealed particle sizes in the range of 5 to 10 nm. In general, this material is superparamagnetic. The magnetic properties are strongly dependent on the precursor. In both cases the production process leads to a highly disordered material with the consequence of a low magnetization. The assumption of a disordered structured is also supported by electron energy loss (EEL) and Moessbauer spectroscopy. The structure of this material shows a nearly identical number of cations on tetrahedral and octahedral lattice sites. {copyright} {ital 1997 Materials Research Society.}
For many years physicists thought small structures would be nearly ideal systems in which to explore and manipulate magnetic interactions. On a small enough length scale the interactions between individual atomic spins cause their magnetic moments to align in the ordered pattern of a single domain, without the complication of domain walls separating regions of varying orientation. For particle sizes at or below that of a single domain, many theoreticalmodels of dynamical behavior predict simple, stable magnets with controllable classical properties. However, as with advances in semiconductor physics, the process of miniaturizing magnetic materials has unexpectedly revealed fascinating new classical and quantum mechanical phenomena. Even the simplest magnetic system, the isolated single‐domain particle, exhibits a wealth of exotic behavior that pushes us to the limits of our present understanding of the fundamentals of magnetism. The study of ever smaller magnets is pushing us to the limits of our understanding of magnetism, providing new headaches for the technologist and new opportunities for the researcher investigating magnetism at the atomic level.
Uniform particles of gamma-Fe2O3 with axial (length/width) ratios from 1 (spheres) to 6.5 (ellipsoids) have been prepared by reduction-oxidation of alpha-Fe2O3. The particles are shown to be single crystals with their long axis collinear to the [111] crystallographic direction for the case of ellipsoidal particles. An increase in cation ordering was observed for gamma-Fe2O3 as the axial ratio decreases, and the particles are completely ordered for spheres. It was observed that the extension of cation ordering in gamma-Fe2O3 particles arises from the amount of defects present in the alpha-Fe2O3 precursor. These results could explain the differences in structural characteristics reported for gamma-Fe2O3 by other authors depending on the experimental conditions.
Experimental measurements of the coercivity and remanence of a fine particle system have been interpreted as arising from a lognormal particle size distribution. Good agreement is obtained between theory and experiment with KVp/kT a constant ≈13, where K is the anisotropy constant, and Vp the critical volume for superparamagnetic behaviour.
The effect of particle size on the formation of vacancy-ordered superstructure in γ-Fe2O3 powders has been investigated by using X-ray, Mössbauer and chemical analyses. Powders of γ-Fe2O3 with different average particle size were prepared by chemical precipitation and subsequent heat-treatment. The X-ray diffraction intensity of the superlattice lines decreases with the particle size of γ-Fe2O3 and finally disappears at a particle-size between 300-175 Å, possibly around 200 Å. Therefore ordering of the cation vacancies in ultrafine γ-Fe2O3 particles is ruled out. Although the vacancies do not form an ordered structure, they do exclusively occupy B-sites.
The electrochemical synthesis of nanoparticles of γ-FeâOâ was performed in an organic medium. The size was directly controlled by the imposed current density, and the resulting particles were stabilized as a colloidal suspension by the use of cationic surfactants. The size distributions of the particles were narrow, with the average sizes varying from 3 to 8 nm. The amorphous character of the nanoparticles was clearly established by X-ray powder diffraction and TEM analysis. The microstructure of this phase could nevertheless be spectroscopically related to maghemite, γ-FeâOâ. âµâ·Fe Mossbauer spectroscopy and magnetization measurements indicated that the dry powders exhibit superparamagnetic behavior at room temperature.
The temperature dependence of the saturation magnetization of iron nanoparticles protected from oxidation by a shell of either magnesium or magnesium fluoride is reported. For iron crystallite sizes ranging from 3 to 18 nm, Bloch’s law is found to hold, but with nonbulk parameters dependent on both size and interface. The Bloch exponent decreases from the bulk value with decreasing size while the Bloch constant increases from the bulk value orders of magnitude with decreasing size. These size dependencies are different for the Mg and MgF2 coated samples to imply important interfacial effects.
Novel isolated magnetic single-domain γ-Fe2O3 nanoclusters have been prepared by coprecipitation of ferrous and ferric salts encapsulated within sol-gel derived silica (SiO2). The nonmagnetic SiO2 coating formed by hydrolysis and polycondensation of tetraethoxysilane on the surface of the Fe2O3 nanoclusters provides a means for thermally stable dispersion of Fe2O3 clusters. The precipitated particles coated with SiO2 are spherical with 4–5 nm diameters. Surface and strain effects played a critical role in determining the overall magnetic behavior of the spherical single-domain particles. Superparamagnetic behavior was observed by superconducting quantum interference device magnetometry and Mössbauer spectroscopy. Superparamagnetic barrier energies and the low-temperature coercivities were modified through cluster/support interface microstructure manipulation. The optical studies showed the absorption edge of the nanocomposites to be slightly blue shifted in the UV–VIS spectrum range when compared to that of bulk γ-Fe2O3. This was attributed to the combined effects of the quantum confinement of the nanocrystalline γ-Fe2O3 clusters and the stress present at the particle/support interface. The magnetic properties can be manipulated via the matrix microstructure, synthesis conditions and thermal treatment. © 1997 American Institute of Physics.
γ-Fe2O3 magnetic nanoparticles, with a very
high surface to volume ratio, exhibit both strong exchange anisotropy
and magnetic training effect. At the same time high field
irreversibility in MH curves and zero field cooled-field cooled (ZFC-FC)
processes has also been detected. A low temperature spin-glass-like
transition is evidenced at TF~42 K with strong
irreversibility even at H = 55 kOe. TFH evolves following the
well known de Almeida-Thouless line
δTF~H2/3. The thermal dependence of the
exchange anisotropy field HE is described by the random-field
model of exchange anisotropy. In the framework of this theory, a surface
spin-glass layer about 0.6 nm thick is determined.
γ–Fe2O3 spherical particles with diameters between 5 and 3.5 nm—very uniform in size—have been prepared by laser pyrolysis of iron pentacarbonyl. The infrared spectra of the samples showed features that indicated different degrees of crystallinity according to the preparation conditions. Low saturation magnetization values (≈10 emu/g) and very high coercivities at low temperature (3000 Oe) have been found for the γ–Fe2O3 nanoparticles with the smaller particle size and the highest structural disorder. To explain the magnetic properties, it was necessary to consider additional anisotropies caused by the increase in surface and structural disorder as the particle size decreased.
Ferrous dodecyl sulfate, Fe(DS)2, micellar solution was used to make nanosized magnetic particles whose size is controlled by the surfactant concentration and by temperature. The average particle size varies from 3.7 to 11.6 nm, with a standard deviation ranging from 0.22 to 0.34. In contrast to what is obtained in homogeneous solution, iron ferrite particles can be obtained when the synthesis is performed at very low reactant concentrations and room temperature. Furthermore, nanoparticles are obtained when the syntheses are performed using Fe(II) as reactant whereas in homogeneous solution particles in the micrometric range are formed. The particle crystallinity varies with the synthesis temperature, going from fairly low values at 25 °C to fairly high values at 50 °C and above. The particles are characterized by superparamagnetic behavior. The saturation magnetization decreases with particle size, which is explained in terms of non-collinear structure at the interface. Particles with low crystallinity are characterized by magnetic diameters smaller than those determined by transmission electron microscopy. This is attributed to crystalline anisotropy.
Understanding the correlation between magnetic properties and nanostructure involves collaborative efforts between chemists, physicists, and materials scientists to study both fundamental properties and potential applications. This article introduces a classification of nanostructure morphology according to the mechanism responsible for the magnetic properties. The fundamental magnetic properties of interest and the theoretical frameworks developed to model these properties are summarized. Common chemical and physical techniques for the fabrication of magnetic nanostructures are surveyed, followed by some examples of recent investigations of magnetic systems with structure on the nanometer scale. The article concludes with a brief discussion of some promising experimental techniques in synthesis and measurements.
The spin-canting effect has been studied in samples of maghemite particles with the same width of about 100 nm, but different length and with different degree of cation disorder. Mössbauer spectra obtained at 5 K with a magnetic field of 4 T applied parallel to the propagation direction of the gamma rays showed that there is a correlation between the degree of structural disorder and the spin-canting effect. The results show that the observed spin canting is not a surface effect, but that atoms in the interior of the particles can be significantly influenced by canting effects.
Ultrafine magnetite particles of average diameter 4–7 nm were prepared by precipitation in a poly(vinylalcohol) (PVA) aqueous solution. Crystallinity of the particles decreased with increasing PVA concentration, while the morphology and particle sizes remained almost unchanged. The dispersion of the magnetite particles prepared at 1 wt% PVA was particularly stable. The saturation magnetization of the particles was above 50 emu/g, in spite of their small size and low crystallinity compared with conventionally prepared fine magnetite particles.
The magnetic properties of γ‐Fe 2 O 3 nanoparticles synthesized by vaporization condensation in a solar image furnace have been studied using both magnetic measurements and Mössbauer spectroscopy. The mean size of the particles turns out to be easily controlled by changing the pressure conditions in the growth chamber. The particles exhibit superparamagnetic behavior at room temperature. Magnetic measurements show the appearance of magnetic hysteresis in the low‐temperature range and from the evolution with temperature of the ferromagnetic ratio, M R /M S , we have determined the distribution of the blocking temperatures for the smallest particles that is fitted to a log‐normal distribution leading to a mean blocking temperature 〈T B 〉=38±15 K. The size distribution of the magnetic unit is also determined from this fitting, as well as from the Mössbauer spectra, obtaining a mean particle volume of about 3.5×10<sup>5</sup> Å<sup>3</sup>. © 1996 American Institute of Physics.
The magnetic properties of gamma-Fe2O3 nanoparticles prepared by spray pyrolysis of dilute solutions of Fe(III) and Fe(II) salts have been investigated using both magnetic measurements and Mossbauer spectroscopy. The most outstanding magnetic features are the strong reduction of the saturation magnetization compared with that of the bulk material, and the existence of magnetic hysteresis up to the highest field used (55 kOe) in both the M(H) loops and the zero-field cooling-field cooling M(T) curves. The magnetic particles exhibit superparamagnetic behavior at room temperature. From the evolution of the ferromagnetic ratio, M-R/M-S, With temperature we have determined the distribution of the blocking temperatures that can be described properly with a log-normal distribution, which allows the determination of mean blocking temperatures [T-B] and mean particle volumes. (C) 1998 American Institute of Physics.
Pure γ-Fe2O3 particles were prepared by a continuous process from cw CO2 laser induced pyrolysis of a 30% solution of iron pentacarbonyl in isopropanol with a yield of about 50% and an average productivity of 0.05 g/h. From TEM the particle size is 5±2 nm with a low degree of aggregation, which agrees with the size obtained from the width of the X-ray diffraction peaks. The nanoparticles seem to be well crystallised according to his infrared spectrum. Moreover, superparamagnetic behaviour was observed at room temperature with a saturation magnetisation value of 30.5 emu/g.
In this paper we examine the applicability of the Gaussian and lognormal probability functions to describe the distribution of particle sizes found in ferrofluids. Measurements have been made of the particle size distributions contained in a large number of ferrofluids prepared by different techniques. From these measurements we conclude that the form of the distribution may be associated with the technique of particle preparation.
The magnetic and morphological properties of fine Fe particles have been studied. Ultrafine particles of Fe were prepared using a vapor deposition technique under an argon atmosphere. The argon pressure was varied from 0.5 to 8 Torr during evaporation, and samples with a median diameter in the range 50-200 angstrom were obtained having a log-normal distribution. The dependence of magnetic properties on particle size and temperature (10 K < T < 300 K) were studied using superconducting-quantum-interference-device magnetometry and Mossbauer spectroscopy. Samples with particle diameter below 90 angstrom showed a superparamagnetic behavior below room temperature. The saturation magnetization of the particles varied from 25 to 190 emu/g, with the higher values corresponding to larger particles. For these larger particles, a coercivity of 1.05 kOe was obtained at room temperature. The magnetic and structural data suggested a core-shell type of structure, where the core consists of metallic Fe and the shell is composed of Fe oxides.
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Zang, D.; Klabunde, K. J.; Sorensen, C. M.; Hadjipanayis, G.
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C. J. J. Appl. Phys. 1998, 83, 3256.
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North-Holland: 1980, 2, 442.