Synthesis of carbon nanotube,graphene, CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript>, and NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript> polypyrrole nanocomposites and study their microwave absorption

In this experimental work, different conductive polymer nanocomposites were synthesized using polypyrrole as conductive polymer and CoFe₂O₄, NiFe₂O₄, CNT and graphene as fillers. X-ray diffraction pattern was used to study the crystallinity of the products and it was found CoFe₂O₄, NiFe₂O₄, CNT, and graphene were successfully embedded in the polymer matrix. To further approve the synthesis of the nanocomposites, energy dispersive X-ray spectroscopy was served. Surface groups of the synthesized nanocomposites were studied by Fourier transform infrared and Raman spectroscopy. The morphology of the products was examined by scanning electron microscopy and transmission electron microscopy. It was found the fillers were successfully embedded in the polymer matrix and they were in nanometer scales. To investigate the magnetic properties and conductivity of the polymer nanocomposites, alternating gradient force magnetometer and four-point probe were used, respectively. Finally, the microwave absorption properties of the polymer nanocomposites were studied and it was found the fillers have different effects on the polymer microwave absorption value.     

Tuning of Dielectric Parameters of (NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript>)<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/CuTl-1223 Nano-superconductor Composites by Temperature and Frequency

Nickel ferrite (NiFe₂O₄) nanoparticles and Cu_0.5Tl_0.5Ba₂Ca₂Cu₃O_10?δ (CuTl-1223) superconductor were prepared separately and then mixed in an appropriate ratios at the final stage to obtain (NiFe₂O₄) _x /CuTl-1223 (x = 0, 0.5, and 1.0 wt%) nano-superconductor composites. There was no significant change observed in crystal structure of the host CuTl-1223 superconducting matrix after the addition of NiFe₂O₄ nanoparticles. The value of zero-resistivity critical temperature { T _{c(R = 0)} (K)} was decreased with increasing content of these nanoparticles in these composites. Maximum values of dielectric loss tangent (tanδ) at lowest possible frequency of 40 Hz were increased with the increase of operating temperature, while its values were decreased and become almost zero at higher frequencies for all these samples at all operating temperatures. A peak in dielectric loss tangent was shifted towards lower frequency values with the addition of these nanoparticles in CuTl-1223 superconducting matrix. The dielectric loss tangent peak was also shifted towards lower frequency values in all these samples with increasing operating temperature, which shows the relaxator-like behavior in these samples. The dielectric parameters of these composites can be tuned by frequency, operating temperatures, and nature and content of these nanoparticles.     

Hydrothermal synthesis and magnetic properties of NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles and nanorods

NiFe₂O₄ nanoparticles and nanorods were synthesized by a facile hydrothermal treatment of Ni(DS)₂ (Nickel dodecyl sulfate), FeCl₃, and NaOH aqueous solution at 120 °C. The products were characterized by powder X-ray diffraction, transmission electron microscopy, and selected area electron diffraction. The magnetic properties were evaluated using a vibrating sample magnetometer. The probable mechanism of the formation of NiFe₂O₄ nanoparticles and nanorods was discussed.     

Fabrication and magnetic properties of NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanocrystalline nanotubes

Aligned NiFe₂O₄ polycrystalline nanotubes have been successfully fabricated inside the nanochannels of porous anodic aluminum oxide (AAO) templates by wetting chemical deposition. A mixture of Fe nitrate and Ni nitrate, which was thermally decomposed at no less than 400 °C, was used to yield NiFe₂O₄ tubes. By varying the deposition conditions and the parameters of the templates, we could tailor the lengths and the outer as well as the inner diameters of the tubes. Transmission electron microscopy (TEM) images reveal that the nanotubes are uniform and well isolated. X-ray diffraction (XRD) and selected area electron diffraction (SAED) demonstrate that the as-obtained nanotubes can be indexed to polycrystalline cubic spinel. The Mössbauer spectra show that the magnetic hyperfine field is reduced with the decrease of the metrical temperature as well as the decrease of the size of nanoparticles.     

Mechanochemically activated synthesis of nanostructured NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript>

Powdery NiFe₂O₄ has been obtained by mechanothermal treatment. Nickel and iron hydroxides are used as initial compounds. For comparison the initial compounds are calcinated without mechanical treatment (samples obtained by direct heating). The characterization of the samples is carried out by XRD analysis and Mössbauer spectroscopy. It is established that single phase NiFe₂O₄ is formed after mechanical activation (5 h) and calcination at 773 K. The ferrite synthesized at this temperature contains a smaller quantity of Fe³⁺ ions in tetrahedral position (31%) than is the case of conventional nickel ferrite (50%). The number of tetrahedrally coordinated iron ions increases with enhancement of the synthesis temperature, approaching the distribution of the tetrahedral and octahedral positions typical of conventional NiFe₂O₄. The samples obtained by direct heating contain unreacted NiO and α-Fe₂O₃ even after calcinations at 1073 K.     

Photocatalytic degradation of methyl orange dye by NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles under visible irradiation: effect of varying the synthesis temperature

Nanoparticles of nickel ferrites (NiFe₂O₄) were synthesized at different temperature of synthesis (25, 50 and 80 °C) through the chemical co-precipitation method. The synthesized powders were characterized using X-ray diffraction for crystallite size and lattice parameter calculation. It reveals the presence of cubic spinel structure of ferrites with crystallite size between 29 and 41 nm. Transmission electron microscopy and scanning electron microscopy showed uniform distribution of ferrite particles with some agglomeration. The Fourier-transform infrared spectroscopy showed absorption bonds, which were assigned to the vibration of tetrahedral and octahedral complexes. Raman spectroscopy is used to verify that we have synthesized ferrite spinels and determines their phonon modes. The thermal decomposition of the NiFe₂O₄ was investigated by TGA/DTA. The optical study UV–visible is used to calculate the band gap energy. Magnetic measurements of the samples were carried out by means of vibrating sample magnetometer and these studies reveal that the formed nickel ferrite exhibits ferromagnetic behavior. Photoluminescence showed three bands of luminescence located at 420, 440 and 535 nm. The photocatalytic properties of nickel ferrite (NiFe₂O₄) nanoparticles were evaluated by studying the photodecomposition of methyl orange as organic pollutant models and showed a good photocatalytic activity.     

Magnetically separable Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@TiO<Subscript>2</Subscript> nanospheres: preparation and photocatalytic activity

A facile and efficient approach for the fabrication of Fe₃O₄@TiO₂ nanospheres with a good core–shell structure has been demonstrated. Products were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS), X-ray diffraction (XRD) and vibrating sample magnetometer (VSM). The results showed that Fe₃O₄@TiO₂ nanocomposites exhibited high degree of crystallinity, excellent magnetic properties at room temperature. Furthermore, the as-prepared Fe₃O₄@TiO₂ nanocomposites exhibited good photocatalytic activity toward the degradation of Rhodamine B (RhB) solution. Additionally, the recycling experiment of Fe₃O₄@TiO₂ nanocomposites had been done, demonstrating that Fe₃O₄@TiO₂ nanocomposites have high efficiency and stability.     

Synthesis and study of magnetic properties of NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles by PVA assisted auto-combustion method

NiFe₂O₄ nanoparticles are prepared by a simple and cost-effective method using via polyvinyl alcohol assisted sol–gel auto-combustion method. The X-ray diffraction result indicated that the synthesized nanoparticles have only the inverse spinel structure without the presence of any other phase impurities. HR-SEM and TEM images showed that the particles are spherical shape with particle size in the range ~11 nm. The magnetic property of these nanoparticles is studied for the enlightening ferrimagnetic behaviour at room temperature. The value of the magnetic saturation (M_s) is 44.3 emug⁻¹, remanent magnetization (M_r) is 19.8 emug⁻¹ and coercive force (H_c) is 672.02 Oe.     

Microstructure and gas-sensing properties of nanocrystalline NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript> prepared by spray pyrolysis

Nanocrystalline nickel ferrite with a crystallite size from 3 to 40 nm has been prepared by spray pyrolysis. The ⁵⁷Fe Mössbauer spectrum of NiFe₂O₄ samples has been found to vary systematically with crystallite size. The sensing response of the nanocrystalline nickel ferrite to 50 ppm NH₃ has been studied using in situ conductance measurements. NiFe₂O₄ offers a strong sensing response to ammonia at the level of its maximum concentration limit. The optimum nickel ferrite crystallite size and temperature for ammonia detection are determined.     

Facile synthesis and characterization of polypyrrole/Co<Subscript>3</Subscript>O<Subscript>4</Subscript> nanocomposites with adjustable intrinsic electroconductivity

Polypyrrole (PPY)/Co₃O₄ nanocomposites (NCs) were synthesized by a facile in situ polymerization of pyrrole in the presence of Co₃O₄ nanoparticles which were obtained by a rheological phase reaction method. The structure and morphology of the as-prepared PPY/Co₃O₄ NCs were investigated by X-ray diffraction, Fourier transform infrared spectra, Raman spectra, scanning electron microscopy and transmission electron microscopy, which confirmed the formation of the nanocomposites and indicated some interactions between PPY chains and Co₃O₄ nanoparticles. Different PPY/Co₃O₄ ratios were selected in order to study conductive properties. The electrical conductivity measurements indicated that ac conductivity tended to remain constant up to about 10⁷ Hz for all samples, and thereafter increased with frequency. The desired electrical properties of PPY/Co₃O₄ NCs can be modulated simply by controlling the contents of Co₃O₄ nanoparticles.     

Synthesis and applications of fluorescent-magnetic-bifunctional dansylated Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@SiO<Subscript>2</Subscript> nanoparticles

Bifunctional magnetic-luminescent dansylated Fe₃O₄@SiO₂ (Fe₃O₄@SiO₂-DNS) nanoparticles were fabricated by the nucleophilic substitution of dansyl chloride with primary amines of aminosilane-modified Fe₃O₄@SiO₂ core–shell nanostructures. The morphology and properties of the resultant Fe₃O₄@SiO₂-DNS nanoparticles were investigated by transmission electron microscopy, FT–IR spectra, UV–vis spectra, photoluminescence spectra, and vibrating sample magnetometry. The Fe₃O₄@SiO₂-DNS nanocomposites exhibit superparamagnetic behavior at room temperature, and can emit strong green light under the excitation of UV light. They show very low cytotoxicity against HeLa cells and negligible hemolysis activity. The T ₂ relaxivity of Fe₃O₄@SiO₂-DNS in water was determined to be 114.6 Fe mM⁻¹ s⁻¹. Magnetic resonance (MR) imaging analysis coupled with confocal microscopy shows that Fe₃O₄@SiO₂-DNS can be uptaken by the cancer cells effectively. All these positive attributes make Fe₃O₄@SiO₂-DNS a promising candidate for both MR and fluorescent imaging applications.     

Temperature-stable and low loss Fe-containing dielectrics in BaO-Ln<Subscript>2</Subscript>O<Subscript>3</Subscript>-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-Ta<Subscript>2</Subscript>O<Subscript>5</Subscript> system

Polycrystalline samples of Ba₄Ln₂Fe₂Ta₈O₃₀ (Ln = La and Nd) were prepared by a high temperature solid-state reaction technique. The formation, structure, dielectric and ferroelectric properties of the compounds were studied. Both compounds are found to be paraelectrics with filled tetragonal tungsten bronze (TB) structure at room temperature. Dielectric measurements revealed that the present ceramics have exceptional temperature stability, a relatively small temperature coefficient of dielectric constant (τ _ε ) of −25 and −58 ppm/°C, with a high dielectric constant of 118 and 96 together with a low dielectric loss of 1.2 × 10⁻³ and 2.8 × 10⁻³ (at 1 MHz) for Ba₄La₂Fe₂Ta₈O₃₀ and Ba₄Nd₂Fe₂Ta₈O₃₀, respectively. The measured dielectric properties indicate that both materials are possible candidates for the fabrication of discrete multilayer capacitors in microelectronic technology.     

Optimized Sol–Gel Chemical Route Using Vacuum Suction for Fabrication of Densely Packed NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript> Nanowires

Highly ordered nanowire arrays of NiFe₂O₄ spinel with a high aspect ratio were fabricated by sol–gel method associated with anodic aluminum oxide (AAO) templates. The preparation of nanowires was carried out by sol–gel method using nickel nitrate, ferric nitrate and citric acid. The molar proportion of nickel nitrate to ferric nitrate and citric acid was 1:2:3. The suction with 0.1 mbar vacuum was used to draw the gel into the AAO nanochannels. The results showed that the lowest annealing temperature is around 600?°C to obtain the single-phase nanostructured NiFe₂O₄. The NiFe₂O₄ nanowires were also uniform and parallel. TEM pictures determined the diameter size of the nanowires of about 100 nm. The magnetic results also showed that the wires have an easy axis of magnetization along their length and they are fully saturated in a field of 7 kOe. It seems that this material could be a good candidate for high perpendicular magnetic storage devices.     

Effects of Mg<Superscript>2+</Superscript> ion substitution on the structural and electric studies of spinel structure of Co<Subscript>1−x</Subscript>Mg<Subscript>x</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript>

In this work, we have prepared Mg substituted CoFe₂O₄ from the transition metals by Sol–Gel Auto combustion method for different concentration (0.00, 0.05, 0.10, 0.15, 0.20 and 0.30) the aqueous materials involved Cobalt Nitrate, Magnesium Nitrate, Ferric nitrate and used a citric acid as a fuel. The final product was calcinated at 850 °C. Powder XRD studies confirmed the crystal structure, FTIR revealed the presence of various functional groups, FE-SEM showed the morphology of the prepared sample. EDAX shows percentage of chemical composition in series of Co ferrites. Dielectric constant, AC Conductivity, Cole–Cole plots, Activation Energy were analysed for the prepared nanoparticles for various frequencies at different temperatures. The dielectric constant values are higher for Mg substituted CoFe₂O₄. The activation energies were also calculated which ranged from 0.1552 to 0.1753 eV for CoFe₂O₄ and Co_1?xMg_xFe₂O₄ materials.     

An alternative method to modify the sensitivity of p-type NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript> gas sensor

Our objective was to determine the role of cooling rate on gas-sensing properties of annealed nano-grained nickel ferrite (NiFe₂O₄). The sol–gel auto combustion method was used for the preparation of NiFe₂O₄. To estimate structural and microstructural features, X-ray diffraction, and scanning electron microscopy techniques were used. For gas-sensing measurements different volatile organic compounds (VOCs) were used as testing gases. To identify the contribution of the different sensing layer elements to the conduction, ac impedance spectroscopy (IS) measurements were performed. It was found that the sensors cooled with lower rate exhibited better sensing performance, due to increase of resistance. Overall, this article covers an alternative method for modifying nickel ferrite gas sensor sensitivity.     

Complex Electric Modulus Spectroscopy of (MnFe<Subscript>2</Subscript>O<Subscript>4</Subscript>)<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/CuTl-1223 Nanoparticles-Superconductor Composites

Manganese ferrite (MnFe₂O₄) nanoparticles and Cu_0.5Tl₀.₅Ba₂Ca₂Cu₃O_10?δ(CuTl-1223) superconducting phase were synthesized by sol-gel and solid-state reaction methods, respectively. Different contents of MnFe₂O₄ nanoparticles were added in CuTl-1223 superconducting matrix to get (MnFe₂O₄)_x/CuTl-1223; x =? 0～2.0 wt% nanoparticles-superconductor composites. Complex electric modulus spectroscopy measurements of (MnFe₂O₄)_x/CuTl-1223 composites were carried out at different test frequencies from 20 Hz to 10 MHz and at different operating temperatures from 78 to 253 K to analyze and interpret the dynamical aspects of electrical transport phenomena (i.e., such as carrier hopping rate, conductivity, and blocking factor). The complex electric modulus spectra showed the effects of both grains and grain-boundaries on electrical properties. The capacitance of grain-boundaries was found higher than that of grains. The capacitive behavior of grains was increased and that of grain-boundaries was decreased with increasing operating temperature for all these samples. Blocking factor of these composites was increased with increasing contents of MnFe₂O₄ nanoparticles. Shifting of peaks in imaginary part of modulus spectra towards lower frequency with increasing contents of these nanoparticles showed non-Debye type relaxation phenomenon in the material.     

Dielectric characteristics of Pb(Zn<Subscript>1/3</Subscript>Ta<Subscript>2/3</Subscript>)O<Subscript>3</Subscript>-BaTiO<Subscript>3</Subscript> ceramics with/without PbTiO<Subscript>3</Subscript> modification

Stabilization tendencies of the perovskite structure in a Pb(Zn_1/3Ta_2/3)O₃-BaTiO₃ pseudobinary system with/without compositional modification by 20 mol% PbTiO₃ introduction were compared. In order to promote perovskite phase formation, the B-site precursor method (which is conceptually similar to the columbite process) was employed in this study. Dielectric properties of sintered samples were investigated as functions of composition and measurement frequency. Dielectric constant spectra, in the paraelectric temperature region, were further analyzed in terms of diffuseness. Microstructures of sintered specimens were also investigated and correlated with perovskite stabilization.     

Magnetic and photocatalytic properties of nanocrystalline ZnMn<Subscript>2</Subscript>O<Subscript>4</Subscript>

The present study describes the synthesis of ZnMn₂O₄ nanoparticles with the spinel structure. These oxide nanoparticles are obtained from the decomposition of metal oxalate precursors synthesized by (a) the reverse micellar and (b) the coprecipitation methods. Our studies reveal that the shape, size and morphology of precursors and oxides vary significantly with the method of synthesis. The oxalate precursors prepared from the reverse micellar synthesis method were in the form of rods (micron size), whereas the coprecipitation method led to spherical nanoparticles of size, 40–50 nm. Decomposition of oxalate precursors at low temperature (∼ 450°C) yielded phase pure ZnMn₂O₄ nanoparticles. The size of the nanoparticles of ZnMn₂O₄ obtained from reverse micellar method is relatively much smaller (20–30 nm) as compared to those made by the co-precipitation (40–50 nm) method. Magnetic studies of nanocrystalline ZnMn₂O₄ confirm antiferro-magnetic ordering in the broad range of ∼ 150 K. The photocatalytic activity of ZnMn₂O₄ nanoparticles was evaluated using photo-oxidation of methyl orange dye under UV illumination and compared with nanocrystalline TiO₂. Dedicated to Prof. C N R Rao on his 75th birthday     

Photoreduction synthesis of silver on Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>/TiO<Subscript>2</Subscript> nanocomposites and their catalytic activity for the degradation of methyl orange

This paper demonstrates the preparation of pure TiO₂, 40% of Bi₂O₃ in TiO₂ and Ag loaded Bi₂O₃/TiO₂ nanocomposites by the hydrothermal method followed by the photoreduction process. The crystal structure, morphology and composition of the samples were characterized by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy respectively. The dispersion of Ag nanoparticles on the surface of Bi₂O₃/TiO₂ nanocomposites are found to bring the conduction band near to the valence band, resulting in the narrow band gap compared to pure TiO₂ and Bi₂O₃/TiO₂ nanocomposites. The XRD analysis demonstrated that silver nanoparticles were dispersed finely on the surface of Bi₂O₃/TiO₂ nanocomposites. All the characterization results revealed that the Ag/Bi₂O₃/TiO₂ nanocomposites were smaller crystallite size, stronger absorbance in the visible region and greater surface area than pure TiO₂ and Bi₂O₃/TiO₂ nanocomposites. The photoluminescence intensity decreases with an increase in the UV-illumination time of Ag loaded Bi₂O₃/TiO₂ revealing a decrease in the recombination rate of electron–hole pairs. In order to test them as a photocatalyst, methyl orange was used as a standard. The photocatalytic degradation of methyl orange shows that the ABT5 sample exhibits the maximum degradation efficiency of 99% within 180 min of irradiation.     

Study on the endocytosis and the internalization mechanism of aminosilane-coated Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles in vitro

In this study, the endocytosis and the internalization mechanism of aminosilane-coated Fe₃O₄ nanoparticles into human lung cancer cell line SPC-A1 was studied compared with human lung cell line WI-38 in vitro. The particle endocytosis behavior was studied by using Transmission Electron Microscope (TEM) and Coupled Plasma-Atomic Emission Spectrometry (ICP-AES). It was found that aminosilane-coated Fe₃O₄ nanoparticles could be greatly taken up by SPC-A1 human cancer cells (202 pg iron/cell) but not by WI-38 human lung cells (13 pg iron/cell). The particles could be retained in SPC-A1 cells over a number of generations in vitro. Different endocytosis was observed by TEM after SPC-A1 cells were treated with different temperature or with/without Cytochalasin B (Inhibitor of phagocytosis) at 37 °C. No nanoparticles were taken up by SPC-A1 after the endocytosis inhibited in low temperature. Restoring the endocytosis activity at 37 °C, the process of nanoparticles from coated pit to endosomes and lysosomes was observed by TEM. Endocytosis activity was effectively inhibited by the presence of Cytochalasin B at 37 °C, while a lot of nanoparticles were uptaken to the cytoplasm of SPC-A1 cells in the control group. Our results suggest that the process of endocytosis of aminosilane-coated Fe₃O₄ nanoparticles can efficiently takes place in lung cancer cells and nanoparticles can be kept in cancer cells for generations. Phagocytosis may be involved in the internalization process of aminosilane-coated Fe₃O₄ nanoparticles.