Barium hexaferrite nanoparticles: morphology-controlled preparation,characterization and investigation of magnetic and photocatalytic properties

In this paper, barium hexaferrite (BaFe₁₂O₁₉) nanoparticles have been successfully synthesized via a simple co-precipitation route. Six chelating agents such as three amino acids (proline, alanine, aspartic acid) and three surfactants (SDBS, PVP, and EDTA) were used. The result showed that the amino acids decrease the particle size and the best result was observed for alanine. Besides, the photocatalyst activity of as-prepared BaFe₁₂O₁₉ nanoparticles was evaluated by degradation of methyl orange under visible light irradiation (λ?>?400 nm). The degradation rates of the methyl orange were measured to be as high as 95% in 200 min. The nanoparticles were also characterized by several techniques including FT-IR, XRD, SEM, and VSM. The VSM measurement showed a saturation magnetization value (Ms) of 30 emu/g.     

The synthesize of CuWO<Subscript>4</Subscript> nano particles by a new morphological control method,characterization of its photocatalytic activity

In various branch of health sciences the nanoparticles are widely used for removing of bacteria, pollutes and etc. However, remove of chemical pollutes like azo dyes, pesticides, cyanide, colors, bacteria, parasites, antibiotics drugs and etc under photocatalytic conditions are still interest. In this work, we synthesized a nonparticle of copper tungstate (CuWO₄) via a co-precipitation method. We also investigated the effect of amino acids such as cysteine, glycine, and valine on morphology and particle size of nanoparticles. The structure and morphology of nano particles were characterized by XRD, SEM, VSM, EDS and DRS spectroscopy methods. The methyl orange (MO) degradation model was used for assessment of photocatalytic properties of as-prepared nanoparticles under UV irradiation. The results have been shown that the CuWO₄ nanoparticles can be decomposed about 81% of MO after 80 min UV irradiation.     

SrFe<Subscript>12</Subscript>O<Subscript>19</Subscript> ferrites and hard magnetic PVA nanocomposite: investigation of magnetization,coecivity and remanence

In this work, various morphologies of SrFe₁₂O₁₉ (SrFe) nanostructures were synthesized via a simple sol–gel method. The effect of concentration, temperature and various surfactants on the morphology and particle size of the magnetic seeds was investigated. The prepared magnetic products were characterized by X-ray diffraction, scanning electron microscopy, and Fourier transform infrared spectroscopy techniques. Alternating gradient force magnetometry reveals that the samples exhibit hard magnetic property with the coercivity up to 5300 Oe. Strontium ferrite was added to poly vinyl alcohol to prepare the magnetic polymeric matrix thin film nanocomposites. The saturation magnetization and coercivity decreased due to agglomeration of magnetic nanoparticles in polymer matrix.     

Functionalization of electrospun magnetically separable TiO<Subscript>2</Subscript>-coated SrFe<Subscript>12</Subscript>O<Subscript>19</Subscript> nanofibers: strongly effective photocatalyst and magnetic separation

Magnetically separable TiO₂-coated SrFe₁₂O₁₉ electrospun nanofibers were obtained successfully by means of sol–gel, electrospinning, and coating technology, followed by heat treatment at 550–650 °C for 3 h. The average diameter of the electrospun fibers was 500–600 nm. The fibers were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), and vibrating sample magnetometer (VSM). The optimized calcining temperature was determined by XRD and the analysis of decolorizing efficiency of methylene blue (MB) under UV–vis irradiation. The photocatalytic activity of the TiO₂-coated SrFe₁₂O₁₉ fibers was investigated using ultraviolet–visible absorbance by following the photooxidative decomposition of a model pollutant dye solution, MB in a photochemical reactor. In contrast to pure TiO₂ fibers, the TiO₂-coated SrFe₁₂O₁₉ fibers have higher absorption in 250–750 nm wavelength regions. The presence of SrFe₁₂O₁₉ not only broadened the response region of visible-light, but also enhanced the absorbance for UV light. The decolorizing efficiency of MB under UV–vis irradiation was up to 98.19%, which was a little higher than that of Degussa P25 (97.68%). Furthermore, these fibers could be recollected easily with a magnet in a photocatalytic process and had effectively avoided secondary pollution of treated water.     

Synthesis,characterization, and investigation of magnetic and photocatalytic property of YbVO<Subscript>4</Subscript> nanoparticles

Nanocrystalline ytterbium vanadate (YbVO₄) was prepared by simple approach based on the reaction between ytterbium nitrate hexahydrate and ammonium metavanadate in water. Besides, three capping agents such as arginine, cysteine, and asparagine were used to investigate their effects on the morphology and particle size of ytterbium vanadate nanoparticles. The formation of pure crystallized YbVO₄ nanocrystals occurred when the precursor was heat-treated at 550 °C in air for 300 min. According to the vibrating sample magnetometer, ytterbium vanadate nanoparticles indicated a paramagnetic behavior at room temperature. Furthermore, the photocatalysis results reveal that the maximum decolorization of 83 % for methyl orange occurred with ytterbium vanadate nanoparticles in 60 min under ultraviolet (UV) light irradiation. The structural, morphological, and optical properties of as-obtained products were characterized by techniques such as XRD, SEM, EDX, and UV–Vis spectroscopy.     

Preparation of nickel ferrite nanoparticles via a new route and study of their photocatalytic properties

Pure nickel ferrite (NiFe₂O₄) were prepared via sol-gel route in presence of different amino acids as a capping agent. The effect of different amino acids such as leucine, asparagine, and cysteine on the size, and morphology of NiFe₂O₄ nanoparticles were investigated. The magnetic properties of the samples were investigated using VSM analyze. We found that the NiFe₂O₄ nanoparticles synthesized at temperature of 800 °C exhibit a ferromagnetic behavior with a saturation magnetization of 34 emu/g and a coercivity of 100 Oe. Furthermore, the photocatalytic properties of as synthesized NiFe₂O₄ were evaluated by degradation of methyl orange as water contaminant. XRD, SEM, EDS, and UV–Vis spectroscopy were employed to characterize structural, morphological, and optical properties of NiFe₂O₄ nanoparticles.     

Magnetic properties of (Co,Al) co-doped SnO<Subscript>2</Subscript> nanoparticles

The desired size of pure SnO₂ and Co (1, 3, 5 mol%) with constant 5 mol% of Al co-doped into SnO₂ nanoparticles are synthesized by chemical co-precipitation method. The raw materials used in synthesis are SnCl₂.2H₂O, AlCl₃, Co (C₂H₃O₂).4H₂O, aqueous NH₄OH and Polyethyleneglycol (PEG) from AR grade. The XRD pattern of pure and co-doped samples confirm the formation of tetragonal rutile phase of SnO₂ nanoparticles with average particle size 25 and 20 nm respectively. Micrographs of scanning electron microscope (SEM) for pure and (Co, Al) co-doped into SnO₂ show that the prepared nanoparticles are agglomerate and spherical in shape. The EDAX spectra of prepared nanoparticles indicate the presence of Co²⁺, Al³⁺, Sn⁴⁺ and O²⁺ and also confirm stoichiometric proportions of raw material in the formation of SnO₂. Transmission electron microscope (TEM) reveals that the surface morphology of pure and co-doped samples are spherical, and average size of particles is ~20 nm. Magnetization measurements from M-H curves of VSM show that the ferromagnetism at low concentration of Co and at higher concentration of Co shows weak ferromagnetism due to super exchange coupling among neighboring ions. The bound magnetic polarons model supports the observed ferromagnetic behavior.     

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     

Preparation and characterization of various morphologies of SrFe<Subscript>12</Subscript>O<Subscript>19</Subscript> nano-structures: investigation of magnetization and coercivity

Hard magnetic SrFe₁₂O₁₉ (SrFe) nanostructures were synthesized by a facile chemical precipitation procedure. The influence of temperature, concentration and different capping agents on the particle size and morphology of the magnetic nanoparticles was investigated. The synthesized ferrites were characterized by X-ray diffraction pattern, scanning electron microscope, and Fourier transform infrared spectroscopy. Ferromagnetic property of the hexaferrite nanostructures was determined by vibrating sample magnetometer. The results show hard magnetic ferrite with a high coercivity about 2800–4000 Oe and saturation magnetization around 11–14 emu/g were synthesized.     

Synthesis of SrFe<Subscript>12</Subscript>O<Subscript>19</Subscript>/SiO<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> composites with core/shell/shell nano-structure and evaluation of their photo-catalytic efficiency for degradation of methylene blue

The SrFe₁₂O₁₉/SiO₂/TiO₂ nanostructures with hard magnetic core were successfully synthesized through the facile and efficient wet chemical processes. At first, nanocrystalline strontium hexaferrite (SrFe₁₂O₁₉) powder was prepared using a new co-precipitation route in ethanol/water media. In the next step, SrFe₁₂O₁₉/SiO₂ composites were produced by well-known Stöber method using tetraethyl orthosilicate as precursor. Finally titania was coated on SrFe₁₂O₁₉/SiO₂ composite particles using titanium n-butoxide precursor. The core/shell/shell nanostructures have been characterized by means of X-ray diffraction, vibrating sample magnetometer, Fourier transform infrared spectra, field emission scanning electron microscopy, and transmission electron microscopy equipped with an energy-dispersive X-ray spectroscopy detector. The catalytic activity of SrFe₁₂O₁₉/SiO₂/TiO₂ composites has been investigated in the degradation of methylene blue dye under UV illumination. The results indicated that the obtained SrFe₁₂O₁₉/SiO₂/TiO₂ composite has photo-catalytic properties and can be retrieved by magnetic separation. The photo-degradation of methylene blue dye was about 80% in the presence of photo-catalyst powder at irradiation time of 180 min. Recycled composite particles could be used again.     

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.     

Effect of amino acids as capping agent on the size and morphology of pure TmVO<Subscript>4</Subscript> nanoparticles and their photocatalyst properties

In this paper, thulium vanadate (TmVO₄) nanoparticles were synthesized via a simple precipitation method based on the reaction between thulium nitrate hexahydrate and ammonium metavanadate in water. Besides, three capping agent such as alanine, valine, and glycine were used to investigate their effects on the morphology and particle size of thulium vanadate nanoparticles. According to the vibrating sample magnetometer, thulium vanadate nanoparticles indicated a paramagnetic behavior at room temperature. In addition, the photocatalyst activity of as-prepared thulium vanadate nanoparticles was evaluated by degradation of methyl orange under ultraviolet light irradiation. The structural, morphological, and optical properties of as-obtained products were characterized by techniques such as XRD, SEM, EDX, and UV–Vis spectroscopy.     

Different morphologies fabrication of NiAl<Subscript>2</Subscript>O<Subscript>4</Subscript> nanostructures with the aid of new template and its photocatalyst application

In the area of water purification, nanotechnology offers the possibility of an efficient removal of pollutants and germs. Nowadays, nanostructures used for detection and removal of chemical and biological substances include metals, azo dyes, nutrients, cyanide, organics, algae, bacteria, parasites, and etc. In the current study, an attempt is made to synthesize and characterization of NiAl₂O₄ nanostructures in an aqueous environment through the simple sol–gel method. Besides, three capping agents as glycine, asparagine, and alanine were used to investigate their effects on the morphology and particle size of NiAl₂O₄ nanostructures. This method starts from of the precursor complex, and involves the formation of homogeneous solid intermediates, reducing atomic diffusion processes during thermal treatment. The formation of pure crystallized NiAl₂O₄ nanocrystals occurred when the precursor was heat-treated at 800 °C in air for 150 min. The stages of the formation of NiAl₂O₄, as well as the characterization of the resulting compounds were done made using UV–Vis diffuse reflectance spectroscopy, field emission scanning electron microscopy, energy dispersive X-ray microanalysis, and X-ray diffraction. The magnetic properties of as-prepared NiAl₂O₄ nanostructures were also investigated with vibrating sample magnetometer. Furthermore, the photocatalytic properties of as synthesized NiAl₂O₄ were evaluated by degradation of methyl orange as water contaminant.     

Synthesis and microwave absorption property of ternary composites: polyaniline/CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/Ba<Subscript>3</Subscript>Co<Subscript>2</Subscript>Fe<Subscript>24</Subscript>O<Subscript>41</Subscript>

Polyaniline (PANI)/CoFe₂O₄/Ba₃Co₂Fe₂₄O₄₁ composite was prepared by an in-situ polymerization method. The phase structure, morphology and magnetic properties of the as-prepared PANI/CoFe₂O₄/Ba₃Co₂Fe₂₄O₄₁ composite were characterized by XRD, FT-IR, SEM, TEM, and VSM, respectively. The microwave absorption properties of the composite were investigated by using a vector network analyzer in the 2–18 GHz frequency range. The results show that the maximum reflection loss value of the PANI/CoFe₂O₄/Ba₃Co₂Fe₂₄O₄₁ composite reaches ?30.5 dB at 10.5 GHz with a thickness of 3 mm and the bandwidth of reflection loss below ?10 dB reaches up to 1.2 GHz. The excellent microwave absorption properties of the as-prepared PANI/CoFe₂O₄/Ba₃Co₂Fe₂₄O₄₁ composite due to the enhanced impedance match between dielectric loss and magnetic loss.     

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.     

A novel spray co-precipitation method to prepare nanocrystalline Y<Subscript>2</Subscript>O<Subscript>3</Subscript> powders for transparent ceramics

A novel spray co-precipitation method was adopted to synthesize well dispersed nanocrystalline Y₂O₃ powders for transparent ceramics. Several analytic techniques such as XRD, SEM, BET and UV–Vis–NIR spectrophotometer were used to determine the properties of coprecipitated powders, and the microstructure and optical properties of as-fabricated ceramics. The influences of the aging time on powders and ceramics were systematically investigated. Precursors were completely reached to yield the Y₂O₃ phase after being calcined at 1250 °C in air. The calcined Y₂O₃ powders exhibited an approximately spherical morphology with narrow size distribution and weak agglomeration, with mean particle size of ~140 nm. The co-precipitated nanopowders with an aging time of 12 h exhibited the best sintering activity due to the low agglomeration, and the in-line transmittance of Y₂O₃ ceramic sintered at 1800 °C for 8 h in vacuum reached to 77.2% at 1064 nm (1 mm thickness).     

Co<Subscript>2</Subscript>SiO<Subscript>4</Subscript> nanostructures/nanocomposites: synthesis and investigations of optical,magnetic, photocatalytic,thermal stability and flame retardant properties

Cobalt orthosilicate (Co₂SiO₄) nanostructures and nanocomposites were successfully synthesized via a sol–gel method, by controlling different conditions. The gels were prepared starting from cobalt (II) acetatete tetrahydrate (Co(CH₃COO)₂·4H₂O), tetraethyl orthosilicate, NH₃ and carbohydrate at calcination temperature 500–700 °C for 5 h. We choose 700 °C as optimum calcination temperature base on XRD results. SEM images showed that NH₃ and glucose are optimum catalysis and capping agent, respectively, in our experimental conditions. For the first time, glucose, fructose, sucrose, maltose and lactose were applied as capping agents to green synthesis of cobalt orthosilicates. The optical and magnetic properties of Co₂SiO₄ nanostructures were investigated by UV–Vis and VSM, respectively. Also, for the first time photocatalytic behavior of these nanostructures was evaluated using UV–Vis and degradation of methyl orange, methylene blue, erythrosine and eosine. DSC and TG curves of the nanocomposites showed both thermal stability and flame retardant property for Co₂SiO₄ nanocomposites prepared in the presence of the PS and PSU.     

Enhanced photoluminescence of CoWO<Subscript>4</Subscript> in CoWO<Subscript>4</Subscript>/PbWO<Subscript>4</Subscript> nanocomposites

CoWO₄/PbWO₄ nanocomposites were successfully synthesized at room temperature (RT) by co-precipitation route without using any templates or surfactants and sintered at 600 °C for good crystallization. The sintered samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy and Zeta potential measurements. UV–Visible diffuse reflectance spectroscopy, photoluminescence (PL) and PL lifetime were studied at RT. The results indicate that the composites have two-phase composition: CoWO₄ and PbWO₄. SEM micrograph and zeta potential measurements reveal particle agglomeration. The intrinsic PL peak emission at 467 nm of CoWO₄ nano sample was enhanced upto four times by optimizing the atomic ratio of Pb/Co concentration. The interconnected interface of CoWO₄/PbWO₄ nanocomposites could have led to increase in number of recombination of electron hole pairs in CoWO₄ and enhanced its intrinsic PL emission intensity. The mechanism of enhanced PL emission for the CoWO₄/PbWO₄ nanocomposites can be attributed to charge transfer between [WO₄]^2? and [WO₆]^6? complexes due to intra particle agglomeration leading to possible interface.     

Samarium-doped Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles with improved magnetic and supercapacitive performance: a novel preparation strategy and characterization

Sm³⁺-doped magnetite (Fe₃O₄) nanoparticles were synthesized through a one-pot facile electrochemical method. In this method, products were electrodeposited on a stainless steel (316L) cathode from an additive-free 0.005 M Fe(NO₃)₃/FeCl₂/SmCl₃ aqueous electrolyte. The structural characterizations through X-ray diffraction, field-emission electron microscopy, and energy-dispersive X-ray indicated that the deposited material has Sm³⁺-doped magnetite particles with average size of 20 nm. Magnetic analysis by VSM revealed the superparamagnetic nature of the prepared nanoparticles (Ms = 41.89 emu g^?1, Mr = 0.12 emu g^?1, and H _Ci = 2.24 G). The supercapacitive capability evaluation of the prepared magnetite nanoparticles through cyclic voltammetry and galvanostat charge–discharge showed that these materials are capable to deliver specific capacitances as high as 207 F g^?1 (at 0.5 A g^?1) and 145 F g^?1 (at 2 A g^?1), and capacity retentions of 94.5 and 84.6% after 2000 cycling at 0.5 and 1 A g^?1, respectively. The results proved the suitability of the electrosynthesized nanoparticles for use in supercapacitors. Furthermore, this work provides a facile electrochemical route for the synthesis of lanthanide-doped magnetite nanoparticles.     

Popcorn like morphology and absence of room temperature ferromagnetism in Ni doped SnO<Subscript>2</Subscript> nanoparticles

Ni-doped SnO₂ nanoparticles were synthesized by the microwave oven assisted solvothermal method. The structural characterization was done by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy. The outcomes confirmed that Ni-doped SnO₂ nanoparticles have a pure rutile-type tetragonal phase of SnO₂ structures with a high degree of crystallization and a crystallite size of 10–14 nm. Popcorn like SEM morphology of the nickel doped sample is shown. Optical characterization was done by UV–Vis spectrometer, fluorescence spectroscopy and electron paramagnetic resonance spectroscopy. Magnetic characterization was done by vibrating sample magnetometer (VSM). The VSM measurements revealed that the Ni doped SnO₂ powder samples were diamagnetic at room temperature. This diamagnetic result is in contradiction to earlier published results.