Spinel Ferrite Nanoparticles: Synthesis, Crystal Structure, Properties, and Perspective Applications

Research Progress on the Preparation of Manganese Dioxide Nanomaterials and Their Electrochemical Applications

Manganese dioxide (MnO2) nanomaterials have shown excellent performance in catalytic degradation and other fields because of their low density and great specific surface area, as well as their tunable chemical characteristics. However, the methods used to synthesize MnO2 nanomaterials greatly affect their structures and properties. Therefore, the present work systematically illustrates common synthetic routes and their advantages and disadvantages, as well as examining research progress relating to electrochemical applications. In contrast to previous reviews, this review summarizes approaches for preparing MnO2 nanoparticles and describes their respective merits, demerits, and limitations. The aim is to help readers better select appropriate preparation methods for MnO2 nanomaterials and translate research results into practical applications. Finally, we also point out that despite the significant progress that has been made in the development of MnO2 nanomaterials for electrochemical applications, the related research remains in the early stages, and the focus of future research should be placed on the development of green synthesis methods, as well as the composition and modification of MnO2 nanoparticles with other materials.

Design of silver-zinc-nickel spinel-ferrite mesoporous silica as a powerful and simply separable adsorbent for some textile dye removal

Silver-zinc-nickel spinel ferrite was prepared by the co-precipitation procedure with the precise composition Ag0.1Zn0.4Ni0.5Fe2O4 for bolstering pollutant removal effectiveness while upholding magnetic properties and then coated with a mesoporous silica layer. The surface characteristics and composition of Ag0.1Zn0.4Ni0.5Fe2O4@mSiO2 were confirmed using EDX, FT-IR, VSM, XRD, TEM, SEM, and BET methods. The surface modification of Ag-Zn-Ni ferrite with a silica layer improves the texture properties, where the specific surface area and average pore size of the spinel ferrite rose to 180 m2/g and 3.15 nm, respectively. The prepared spinel ferrite@mSiO2 has been utilized as an efficient adsorbent for eliminating methyl green (MG) and indigo carmine (IC) as models of cationic and anionic dyes from wastewater, respectively. Studying pH, Pzc, adsorbent dosage, dye concentration, and temperature showed that efficient removal of MG was carried out in alkaline media (pH = 12), while the acid medium (pH = 2) was effective for IC removal. Langmuir isotherm and pseudo-second-order kinetics were found to be good fits for the adsorption data. Both dyes were adsorbed in a spontaneous, endothermic process. A possible mechanism for dye removal has been proposed. The adsorbent was effectively recovered and reused.

Interface Structures on Mechanically Polished Surface of Spinel Ferrite and Its Effect on the Magnetic Domains

Soft magnetic spinel ferrites are indispensable parts in devices such as transformers and inductors. Mechanical surface processing is a necessary step to realize certain shapes and surface roughness in producing the ferrite but also has a negative effect on the magnetic properties of the ferrite. In the past few years, a new surface layer was always believed to form during the mechanical surface processing, but the change of atomic structure on the surface and its effect on the magnetic structure remain unclear. Herein, an interface structure consisting of a rock-salt sublayer, distorted NiFe2O4 sublayer, and pristine NiFe2O4 was found to form on mechanically polished single-crystal NiFe2O4 ferrite. Such an interface structure is produced by phase transformation and lattice distortion induced by the mechanical processing. The magnetic domain observation and electrical property measurement also indicate that the magnetic and electrical anisotropy are both enhanced by the interface structure. This work provides deep insight into the surface structure evolution of spinel ferrite by mechanical processing.

High-density polyethylene composites filled with micro- and nano-particles of nickel ferrite: magnetic, mechanical, and thermal properties

With the increasing demand of new magnetic materials for modern technological application alternatives to conventional magnetic materials, the development of lightweight polymer magnetic composites has become a prominent research area. For this perspective, a new magnetic material was developed using 30 wt% nickel ferrite micro and nanoparticles as fillers for a high-density polyethylene matrix. The development process began with the synthesis of NF-micro and NF-nanoparticles using solid-state and co-precipitation techniques, respectively, followed by extrusion molding and injection molding. The success of the synthesis process and the purity of the spinel structure phase were confirmed. Additionally, using the extrusion process produced polymer magnetic composite materials with a good distribution of magnetic particles within the polymer matrix, resulting in good magnetic properties and enhanced mechanical properties of the polymer magnetic materials.

Radio-Absorbing Magnetic Polymer Composites Based on Spinel Ferrites: A Review

Ferrite-containing polymer composites are of great interest for the development of radar-absorbing and -shielding materials (RAMs and RSMs). The main objective of RAM and RSM development is to achieve a combination of efficient electromagnetic wave (EMW) absorption methods with advantageous technological and mechanical properties as well as acceptable weight and dimensions in the final product. This work deals with composite RAMs and RSMs containing spinel-structured ferrites. These materials are chosen since they can act as efficient RAMs in the form of ceramic plates and as fillers for radar-absorbing polymer composites (RAC) for electromagnetic radiation (EMR). Combining ferrites with conducting fillers can broaden the working frequency range of composite RAMs due to the activation of various absorption mechanisms. Ferrite-containing composites are the most efficient materials that can be used as the working media of RAMs and RSMs due to a combination of excellent dielectric and magnetic properties of ferrites. This work contains a brief review of the main theoretical standpoints on EMR interaction with materials, a comparison between the radar absorption properties of ferrites and ferrite-polymer composites and analysis of some phenomenological aspects of the radar absorption mechanisms in those composites.

Effect of particle size and composition on local magnetic hyperthermia of chitosan-Mg1-xCoxFe2O4 nanohybrid

In this study, Mg1-xCoxFe2O4 (0≤x ≤ 1 with ∆x = 0.1) or MCFO nanoparticles were synthesized using a chemical co-precipitation method and annealed at 200, 400, 600, and 800°C respectively to investigate the structural properties of the materials by X-ray diffractometer (XRD), transmission electron microscopy (TEM), and Fourier-transform infrared spectroscopy (FTIR). Controlled annealing increased particle size for each value of x. The aim was to investigate how specific loss power (SLP) and maximum temperature (Tmax) during local magnetic hyperthermia were affected by structural alterations associated with particle size and composition. The lattice parameter, X-ray density, ionic radius, hopping length, bond length, cation-cation distance, and cation-anion distance increase with an increase in Co2+ content. Raman and FTIR spectroscopy reveal changes in cation distribution with Co2+ content and particle size. Magnetic properties measured by the physical property measurement system (PPMS) showed saturation magnetization (Ms), coercivity (Hc), remanent magnetization (Mr/Ms), and anisotropy constant (K1) of the Mg1-xCoxFe2O4 nanoparticles increase with Co2+ content and particle size. When exposed to an rf magnetic field, the nanohybrids experienced an increase in both the SLP (specific loss power) and Tmax (maximum temperature) as the particle size initially increased. However, these values reached their peak at critical particle size and subsequently decreased. This occurs since a modest increase in anisotropy, resulting from the presence of Co2+ and larger particle size, facilitates Néel and Brownian relaxation. However, for high anisotropy values and particle size, the Néel and Brownian relaxations are hindered, leading to the emergence of a critical size. The critical size increases as the Co2+ content decreases, but it decreases as the Co2+ content increases, a consequence of higher anisotropy with the increase in Co2+. Additionally, it is noteworthy that the maximum temperature (Tmax) rises as the concentration of nanohybrids grows, but the specific loss power (SLP) decreases. An increased concentration of chitosan-MCFO nanohybrids inhibits both the Néel and Brownian relaxation processes, reducing specific loss power.

Interplay of Anisotropy Energy Barrier and Self-Heating Efficiency of Cobalt-Substituted CuFe2O4 Nanoparticles

In this study, we delve into the intricate interplay between the anisotropy energy barrier and the self-heating efficiency of magnetic nanoparticles (MNPs). We embarked on this exploration by synthesizing Cu1-xCoxFe2O4 (x = 0, 0.1, 0.3, and 0.5) MNPs using a straightforward coprecipitation method. Our magnetic assessments, conducted at different temperatures, unveiled a notable trend as we traversed from x = 0.1 to x = 0.5. Specifically, we observed a consistent increase in saturation magnetization, coercivity, and remanence. This pattern also extended to the anisotropy energy barrier, which was derived from the effective anisotropy constant determined through the temperature dependency of the coercivity method. However, an intriguing twist emerged when we scrutinized the specific absorption rate (SAR), calculated via the Box-Lucas method. Contrary to much of the existing literature, our experimental results showcased a decline in SAR concerning x. This experimental work challenges the conventional understanding of the relationship between the anisotropy energy barrier and the SAR value of these nanoparticles. This study prompts us to reconsider the intricate mechanisms governing the relaxation of magnetic moments and subsequent heat release when subjected to an alternating magnetic field. By doing so, we aim to gain fresh insights into the self-heating properties of MNPs and optimize their utilization to better understand their heat-release properties and ensure that they are used as efficiently as possible in a variety of biomedical applications.

Newly Synthesized CoFe2-xDyxO4 (x = 0; 0.1; 0.2; 0.4) Nanoparticles Reveal Promising Anticancer Activity against Melanoma (A375) and Breast Cancer (MCF-7) Cells

The current study focuses on the synthesis via combustion of dysprosium-doped cobalt ferrites that were subsequently physicochemically analyzed in terms of morphological and magnetic properties. Three types of doped nanoparticles were prepared containing different Dy substitutions and coated with HPGCD for higher dispersion properties and biocompatibility, and were later submitted to biological tests in order to reveal their potential anticancer utility. Experimental data obtained through FTIR, XRD, SEM and TEM confirmed the inclusion of Dy3+ ions in the nanoparticles' structure. The size of the newly formed nanoparticles ranged between 20 and 50 nm revealing an inverse proportional relationship with the Dy content. Magnetic studies conducted by VSM indicated a decrease in remanent and saturation mass magnetization, respectively, in Dy-doped nanoparticles in a direct proportionality with the Dy content; the decrease was further amplified by cyclodextrin complexation. Biological assessment in the presence/absence of red light revealed a significant cytotoxic activity in melanoma (A375) and breast (MCF-7) cancer cells, while healthy keratinocytes (HaCaT) remained generally unaffected, thus revealing adequate selectivity. The investigation of the underlying cytotoxic molecular mechanism revealed an apoptotic process as indicated by nuclear fragmentation and shrinkage, as well as by Western blot analysis of caspase 9, p53 and cyclin D1 proteins. The anticancer activity for all doped Co ferrites varied was in a direct correlation to their Dy content but without being affected by the red light irradiation.

Towards hard-magnetic behavior of CoFe2O4 nanoparticles: a detailed study of crystalline and electronic structures, and magnetic properties

We have used the coprecipitation and mechanical-milling methods to fabricate CoFe2O4 nanoparticles with an average crystallite size (d) varying from 81 to ∼12 nm when changing the milling time (t m) up to 180 min. X-ray diffraction and Raman-scattering studies have proved the samples crystalizing in the spinel structure. Both the lattice constant and residual strain tend to increase when t m(d) increases (decreases). The analysis of magnetization data has revealed a change in the coercivity (H c) towards the hard-magnetic properties. Specifically, the maximum H c is about 2.2 kOe when t m = 10 min corresponding to d ≈ 29 nm; beyond this t m(d) value, H c gradually decreases. Meanwhile, the increase of t m always reduces the saturation magnetization (M s) from ∼69 emu g-1 for t m = 0 to 35 emu g-1 for t m = 180 min. The results collected as analyzing X-ray absorption data have indicated a mixed valence state of Fe2+,3+ and Co2+ ions. We think that the migration and redistribution of these cations between the tetrahedral and octahedral sites together with lattice distortions and defects induced by the milling process have impacted the magnetic properties of the CoFe2O4 nanoparticles.

Scale-up approach for the preparation of magnetic ferrite nanocubes and other shapes with benchmark performance for magnetic hyperthermia applications

Magnetic nanoparticles are increasingly used in medical applications, including cancer treatment by magnetic hyperthermia. This protocol describes a solvothermal-based process to prepare, at the gram scale, ferrite nanoparticles with well-defined shape, i.e., nanocubes, nanostars and other faceted nanoparticles, and with fine control of structural/magnetic properties to achieve point-of-reference magnetic hyperthermia performance. This straightforward method comprises simple steps: (i) making a homogeneous alcoholic solution of a surfactant and an alkyl amine; (ii) adding an organometallic metal precursor together with an aldehyde molecule, which acts as the key shape directing agent; and (iii) reacting the mixture in an autoclave for solvothermal crystallization. The shape of the ferrite nanoparticles can be controlled by the structure of the aldehyde ligand. Benzaldehyde and its aromatic derivatives favor the formation of cubic ferrite nanoparticles while aliphatic aldehydes result in spherical nanoparticles. The replacement of the primary amine, used in the nanocubes synthesis, with a secondary/tertiary amine results in nanoparticles with star-like shape. The well-defined control in terms of shape, narrow size distribution (below 5%), compositional tuning and crystallinity guarantees the preparation, at the gram scale, of nanocubes/star-like nanoparticles that possess, under magnetic field conditions of clinical use, specific adsorption rates comparable to or even superior to those obtained through thermal decomposition methods, which are typically prepared at the milligram scale. Here, gram-scale nanoparticle products with benchmark features for magnetic hyperthermia applications can be prepared in ~10 h with an average level of expertise in chemistry.

Application of magnesium ferrite nanomaterials for adsorptive removal of arsenic from water: Effects of Mg and Fe ratio

Magnesium ferrites (MgFe₂O₄) drew much attention in water treatment because of higher stability, magnetic properties, availability and higher safety. MgFe₂O₄ having different Fe and Mg ratios were synthesized through a simple one-step solvothermal method and applied for the removal of toxic arsenic oxyanions from water. Three different magnesium ferrites, MF_0.1, MF_0.2 and MF_0.33, were synthesized using molar Mg and Fe ratio of 10:90, 20:80 and 33:67, respectively. The Mg and Fe ratio affected the physical and magnetic properties, surface area, crystallite size, pore diameter and magnetism, of magnesium ferrites, which were evidenced by the XRD, SEM-EDS, BET and VSM. Increasing Mg content reduced the pore size, pore volume and saturation magnetization but increased surface area and pH_PZC. It was estimated that defective iron oxide, γ-Fe₂O₃ maghemite, had been formed with the magnesium ferrites, when the ratios of Mg and Fe were non-stoichiometric. The difference in characteristics of magnesium ferrites synthesized with three ratios of Mg and Fe affected arsenic adsorption capacity and the stability of adsorbed arsenic. Arsenic adsorption data followed Freundlich isotherm model and maximum As(III) and As(V) adsorption capacities were found to be 51.48, 100.53, 103.94 mg/g and 26.06, 43.44, 45.52 mg/g by MF_0.1, MF_0.2 and MF_0.33, respectively. Fast adsorption of arsenic was confirmed by kinetic data which followed the Pseudo-2nd-order kinetic model. The MF_0.33 having stoichiometric ratio of Mg and Fe showed higher adsorption capacity and stability for arsenic than the other two at neutral pH.

Microwave-Enhanced Crystalline Properties of Zinc Ferrite Nanoparticles

Two series of ZnFe₂O₄ mixed cubic spinel nanoparticles were prepared by a coprecipitation method, where a solution of Fe³⁺ and Zn²⁺ was alkalised by a solution of NaOH. While the first series was prepared by a careful mixing of the two solutions, the microwave radiation was used to enhance the reaction in the other series of samples. The effect of the microwave heating on the properties of the prepared particles is investigated. X-ray powder diffraction (XRD), ⁵⁷Fe Mössbauer spectroscopy and magnetometry were employed to prove the cubic structure and superparamagnetic behavior of the samples. The particle size in the range of nanometers was investigated by a transmission electron microscopy (TEM), and the N₂ adsorption measurements were used to determine the BET area of the samples. The stoichiometry and the chemical purity were proven by energy dispersive spectroscopy (EDS). Additionally, the inversion factor was determined using the low temperature Mössbauer spectra in the external magnetic field. The microwave heating had a significant effect on the mean coherent length. On the other hand, it had a lesser influence on the size and BET surface area of the prepared nanoparticles.

Biocompatibility and colorectal anti-cancer activity study of nanosized BaTiO3 coated spinel ferrites

In the present work, different nanoparticles spinel ferrite series (MFe2O4, Co0.5M0.5Fe2O4; M = Co, Mn, Ni, Mg, Cu, or Zn) have been obtained via sonochemical approach. Then, sol-gel method was employed to design core-shell magnetoelectric nanocomposites by coating these nanoparticles with BaTiO3 (BTO). The structure and morphology of the prepared samples were examined by X-ray powder diffraction (XRD), scanning electron microscope (SEM) coupled with energy dispersive X-ray spectroscopy (EDX), high-resolution transmission electron microscope (HR-TEM), and zeta potential. XRD analysis showed the presence of spinel ferrite and BTO phases without any trace of a secondary phase. Both phases crystallized in the cubic structure. SEM micrographs illustrated an agglomeration of spherical grains with nonuniformly diphase orientation and different degrees of agglomeration. Moreover, HR-TEM revealed interplanar d-spacing planes that are in good agreement with those of the spinel ferrite phase and BTO phase. These techniques along with EDX analyses confirmed the successful formation of the desired nanocomposites. Zeta potential was also investigated. The biological influence of (MFe2O4, CoMFe) MNPs and core-shell (MFe2O4@BTO, CoMFe@BTO) magnetoelectric nanocomposites were examined by MTT and DAPI assays. Post 48 h of treatments, the anticancer activity of MNPs and MENCs was investigated on human colorectal carcinoma cells (HCT-116) against the cytocompatibility of normal non-cancerous cells (HEK-293). It was established that MNPs possess anti-colon cancer capability while MENCs exhibited a recovery effect due to the presence of a protective biocompatible BTO layer. RBCs hemolytic effect of NPs has ranged from non- to low-hemolytic effect. This effect that could be attributed to the surface charge from zeta potential, also the CoMnFe possesses the stable and lowest zeta potential in comparison with CoFe2O4 and MnFe2O4 also to the protective effect of shell. These findings open up wide prospects for biomedical applications of MNPs as anticancer and MENCs as promising drug nanocarriers.

Engineered magnetic oxides nanoparticles as efficient sorbents for wastewater remediation: a review

The rapid urbanization and industrialization is causing worldwide water pollution, calling for advanced cleaning methods. For instance, pollutant adsorption on magnetic oxides is efficient and very practical due to the easy separation from solutions by an magnetic field. Here we review the synthesis and performance of magnetic oxides such as iron oxides, spinel ferrites, and perovskite oxides for water remediation. We present structural, optical, and magnetic properties. Magnetic oxides are also promising photocatalysts for the degradation of organic pollutants. Antimicrobial activities and adsorption of heavy metals and radionucleides are also discussed.

Magnetic and optical properties of green synthesized nickel ferrite nanoparticles and its application into photocatalysis

Spinel NiFe₂O₄nanoparticles have been synthesized via hydrothermal route usingMangifera indicaflower extract (MIFE) as a green surfactant and reducing agent. X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy techniques have been used to determine the structure and morphology. The formation of single-phase, monodispersed NiFe₂O₄with mixed morphology, the predominant shape being of equi-axed nanoparticles having an average particle size ≲45 nm, is observed. The thermal magnetization of as-synthesized NiFe₂O₄nanoparticles shows ferromagnetic to paramagnetic phase transition atT_c ∼ 825 K. These nanoparticles show a very high saturation magnetization (M_s) value of 55 emu g^-1close to the bulk material and amongst the highest reported values for green synthesized NiFe₂O4 nanoparticles. This material has a coercivity (H_c) of 0.15 kOe and remanent magnetization (M_r) of 8.5 emu g^-1. The as-synthesized NiFe₂O₄nanoparticles show bandgap energy of 2.02 eV, derived from UV-vis absorption measurement, which is suitable for effective solar photocatalytic reactions. When exposed to sunlight in the presence of as-synthesized NiFe₂O₄nanoparticles, 93% of MB-dye degradation is measured in 80 min, indicating excellent photocatalytic properties. Based on the as-synthesized NiFe₂O₄nanoparticles' observed properties, the effectiveness of MIFE as an environmentally friendly surfactant, and the low-cost dye-degradation prospects of green synthesized NiFe₂O₄nanoparticles are affirmed.

A Au/CuNiCoS4/p-Si photodiode: electrical and morphological characterization

In this present work, CuNiCoS₄ thiospinel nanocrystals were synthesized by hot injection and characterized by X-ray diffractometry (XRD), high-resolution transmission electron microscopy (HR-TEM), and energy-dispersive X-ray spectroscopy (EDS). The XRD, EDS, and HR-TEM analyses confirmed the successful synthesis of CuNiCoS₄. The obtained CuNiCoS₄ thiospinel nanocrystals were tested for photodiode and capacitance applications as interfacial layer between Au and p-type Si by measuring I-V and C-V characteristics. The fabricated Au/CuNiCoS₄/p-Si device exhibited good rectifying properties, high photoresponse activity, low series resistance, and high shunt resistance. The C-V characteristics revealed that capacitance and conductance of the photodiode are voltage-and frequency-dependent. The fabricated device with CuNiCoS₄ thiospinel nanocrystals can be employed in high-efficiency optoelectronic applications.

Magnetoliposomes Based on Shape Anisotropic Calcium/Magnesium Ferrite Nanoparticles as Nanocarriers for Doxorubicin

Multifunctional lipid nanocarriers are a promising therapeutic approach for controlled drug release in cancer therapy. Combining the widely used liposome structure with magnetic nanoparticles in magnetoliposomes allies, the advantages of using liposomes include the possibility to magnetically guide, selectively accumulate, and magnetically control the release of drugs on target. The effectiveness of these nanosystems is intrinsically related to the individual characteristics of the two main components—lipid formulation and magnetic nanoparticles—and their physicochemical combination. Herein, shape-anisotropic calcium-substituted magnesium ferrite nanoparticles (Ca_0.25Mg_0.75Fe₂O₄) were prepared for the first time, improving the magnetic properties of spherical counterparts. The nanoparticles revealed a superparamagnetic behavior, high saturation magnetization (50.07 emu/g at 300 K), and a large heating capacity. Furthermore, a new method for the synthesis of solid magnetoliposomes (SMLs) was developed to enhance their magnetic response. The manufacturing technicalities were optimized with different lipid compositions (DPPC, DPPC/Ch, and DPPC/DSPE-PEG) originating nanosystems with optimal sizes for biomedical applications (around or below 150 nm) and low polydispersity index. The high encapsulation efficiency of doxorubicin in these magnetoliposomes was proven, as well as the ability of the drug-loaded nanosystems to interact with cell membrane models and release DOX by fusion. SMLs revealed to reduce doxorubicin interaction with human serum albumin, contributing to a prolonged bioavailability of the drug upon systemic administration. Finally, the drug release kinetic assays revealed a preferable DOX release at hyperthermia temperatures (42 °C) and acidic conditions (pH = 5.5), indicating them as promising controlled release nanocarriers by either internal (pH) and external (alternate magnetic field) stimuli in cancer therapy.

Investigation on anneal-tuned properties of ZnFe2O4 nanoparticles for use in humidity sensors

The effect of different annealing temperatures on structural, optical and magnetic properties of ZnFe2O4 nanoparticles prepared using the coprecipitation technique has been investigated. With the increase in annealing temperature, crystallinity and average crystallite size of nanoparticles increased. The average crystallite size was found to be 5.55 nm, 6.62 nm and 32.9 nm for the samples annealed at 300 °C, 500 °C and 700 °C, respectively. The X-ray diffraction and Fourier-transform infrared spectroscopy revealed the formation of a cubic spinel structure. The optical direct and indirect bandgap energy decreased with an increase in annealing temperature. The saturation magnetization increased from 16.38 emu/g to 25.91 emu/g. The M-H curves depicted the magnetic phase transition from superparamagnetic to ferrimagnetic. The electrical properties were investigated using an impedance analyzer in the frequency range of 300 Hz to 1 MHz. The conduction properties showed enhancement with increased annealing. The humidity sensing properties were investigated in the range of 15-90% RH and revealed a strong dependence of adsorption capacity on the annealing temperature. Electrical conductivity improved with increased humidity. Excellent humidity sensitivity was observed for ferrites annealed at 700 °C attributed to increased crystallinity and reduced lattice strain making them a potential candidate for use in humidity sensors.

Current scenario of CNG vehicular pollution and their possible abatement technologies: an overview

Compressed natural gas is an alternative green fuel for automobile industry. Recently, the Indian government is targeting to replace all the conventional fuel vehicles by compressed natural gas (CNG) automobiles due to its several merits. Still, the presence of a significant amount of CO, CH₄, and NO_x gases in the CNG vehicle exhaust are quiet a matter of concern. Thus, to control the emissions from CNG engines, the major advances are under development of and oxidation is one of them in catalytic converter. In literature, the catalysts such as noble and non-noble metals have been reported for separate oxidation of CO and CH_4.. Experimentally, it was found that non-noble metal catalysts are preferred due to its low cost, good thermal stability, and molding tractability. In literature, several articles have been published for CO and CH₄ oxidation but no review paper is still available. Thus, the present review provides a comprehensive overview of separate as well as simultaneous CO and CH₄ oxidation reactions for CNG vehicular emission control.

Induction Heating Analysis of Surface-Functionalized Nanoscale CoFe2O4 for Magnetic Fluid Hyperthermia toward Noninvasive Cancer Treatment

Oleic acid-coated cobalt ferrite nanoparticles were synthesized using the chemical co-precipitation route and characterized by standard techniques for structure, morphology, and magnetic properties analysis. The Rietveld refined X-ray diffraction (XRD) pattern of CoFe2O4 nanoparticles indicated the formation of a cubic-spinel single-phase structure with the Fd3̅m space group. The average crystallite size (∼12 nm) confirmed the nanocrystalline appearance of the prepared CoFe2O4 nanoparticles. Transmission electron microscopy (TEM) images revealed the spherical nature of both (CoFe2O4) and (OA-CoFe2O4) samples. The absorption bands in the Fourier transform infrared (FT-IR) spectrum at ∼3418, 3026, 1628, 1404, 1068, 845, 544, and 363 cm-1 affirmed the spinel ferrite formation and OA attachment. The M-H curve recorded at room temperature showed the superparamagnetic nature of the CoFe2O4 nanoparticles with moderate saturation magnetization (∼78 emu/gm). The blocking temperature of the prepared CoFe2O4 nanoparticles obtained from the field-cooled and zero-field-cooled (FC-ZFC) curve was estimated to be 144 K. Further, the characterized surface-modified CoFe2O4 was then added in ethylene glycol/water with various concentrations and characterized by the induction heating technique for the evaluation of their self-heating characteristics. A series of temperature versus time measurements were made by varying the ethylene glycol/water proportion for better understanding of the self-heating characteristics of the prepared CoFe2O4 nanoparticles. All of the findings display the applicability of the surface-modified CoFe2O4 nanoparticles in magnetic fluid hyperthermia toward noninvasive cancer treatment and other bio-applications.

The Immobilized Copper on Nickel Ferrite: A Magnetically Superior Nanocatalyst for Chemoselective and Knoevenagel Synthesis of Bisdimedones and 1,8-Dioxo-octahydroxanthenes under Solvent-Free Conditions

AIM AND OBJECTIVE

Nowadays, bisdimedones and 1,8-dioxo-octahydroxanthenes are considered as biologically active materials. Due to this, the synthesis of the mentioned materials is the subject of more interest. Although most of the reported methods have their own merits, however, they generally require the use of expensive reagents, hazardous organic solvents, a tedious workup procedure and reduced recyclability of the applied catalyst system. Overcoming of the above mentioned drawbacks, therefore, encouraged us to investigate the capability of nanostructured NiFe2O4@Cu towards the synthesis of bisdimedones and 1,8- dioxo-octahydroxanthenes under green reaction conditions.

MATERIALS AND METHODS

Nanoparticles of NiFe2O4@Cu were prepared via a two-step procedure including the preparation of NiFe2O4 by solid-state grinding of Ni(OAc)2·4H2O and Fe(NO3)3·9H2O in the presence of NaOH followed by the immobilization of Cu(0) on the surface of NiFe2O4 nucleus via hydrazine hydrate reduction of Cu(NO3)2·3H2O.

RESULTS

After the synthesis of NiFe2O4@Cu, the catalytic activity of the Cu-nanocatalyst towards Knoevenagel reaction of aromatic aldehydes with dimedone under different reaction conditions was investigated. The examinations showed that using the molar equivalents of aromatic aldehydes (1 mmol) and dimedone (2 mmol) in the presence of 0.15 g NiFe2O4@Cu under solvent-free conditions chemoselectively afforded structurally different bisdimedone products at 60°C and 1,8-dioxo-octahydroxanthenes at 120°C.

CONCLUSION

In this study, magnetically, nanoparticles of NiFe2O4@Cu were prepared and then characterized using different analyses. The catalytic activity of the prepared Cu-nanocatalyst was also studied towards solvent-free Knoevenagel condensation of aromatic aldehydes with dimedone. All the reactions were carried out within 15-240 min to afford bisdimedone and 1,8-dioxo-octahydroxanthene products in high yields.

Recent advancements in manganite perovskites and spinel ferrite-based magnetic nanoparticles for biomedical theranostic applications

Recently, magnetic nanoparticles (MNPs) based on manganite perovskites (La_1-xSr_xMnO₃ or LSMO) and/or spinel ferrites (i.e. SPFs with the formula MFe₂O₄; M=Co, Mg, Mn, Ni and Zn and mixed SPFs (e.g. Co-Zn, Mg-Mn, Mn-Zn and/or Ni-Zn)) have garnered great interest in magnetic hyperthermia therapy (MHT) as heat-inducing agents due to their tuneable magnetic properties including Curie temperature (T _c) to generate controllable therapeutic temperatures (i.e. 42 °C-45 °C)-under the application of an alternating magnetic field (AMF)-for the treatment of cancer. In addition, these nanoparticles are also utilized in magnetic resonance imaging (MRI) as contrast-enhancing agents. However, the employment of the LSMO/SPF-based MNPs in these MHT/MRI applications is majorly influenced by their inherent properties, which are mainly tuned by the synthesis factors. Therefore, in this review article, we have systematically discussed the significant chemical methods used to synthesize the LSMO/SPF-based MNPs and their corresponding intrinsic physicochemical properties (size/shape/crystallinity/dispersibility) and/or magnetic properties (including saturation magnetization (M _s)/T _c). Then, we have analyzed the usage of these MNPs for the effective imaging of cancerous tumors via MRI. Finally, we have reviewed in detail the heating capability (in terms of specific absorption rate) of the LSMO/SPF-based MNPs under calorimetric/biological conditions for efficient cancer treatment via MHT. Herein, we have mainly considered the significant parameters-such as size, surface coating (nature and amount), stoichiometry, concentration and the applied AMFs (including amplitude (H) and frequency (f))-that influence the heat induction ability of these MNPs.

Structure–redox reactivity relationships in Co1−xZnxFe2O4: the role of stoichiometry

The strong relation between the cationic distribution and catalytic properties of Co–Zn ferrite nanoparticles was studied and the new antistructure modeling approach has been proposed for identification of the active centers in the redox reaction.