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.     

Preparation of sheet like polycrystalline NiFe2O4 nanostructure with PVA matrices and their properties

Sheet-like nickel ferrite (NiFe₂O₄) has been synthesised with PVA matrices using co-precipitation technique. The sheet is formed from the oriented aggregation of single crystalline NiFe₂O₄ nanoparticles with PVA as the structure directing template. The synthesised materials are characterised based on X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), high-resolution scanning electron microscopy (HRSEM), Fourier transform infrared spectroscopy (FTIR) and vibrating sample magnetometry (VSM). The XRD results show that the nanocrystal contains single phase spinel structure of Fd3m space group. The existence of PVA with nanoparticles has been confirmed by FTIR spectra. The room temperature ferromagnetic property is exhibited by the as synthesised sample with high saturation magnetisation.     

Paederia foetida Linn. promoted synthesis of CoFe2 O4 and NiFe2 O4 nanostructures and their photocatalytic efficiency

A facile method of synthesis of cobalt ferrite (CoFe₂ O₄) and nickel ferrite (NiFe₂ O₄) nanoparticles (NPs) was developed using urea as a hydroxylating agent and Paederia foetida Linn. (family: Rubiaceae) leaf extract as a bio‐template. The synthesised ferrite NPs were characterised in a detailed manner by powder X‐ray diffraction (XRD), transmission electron microscopy, Fourier transform‐infrared spectroscopy and vibrating sample magnetometer analysis. The XRD patterns revealed the formation of cubic face‐centred phase for both CoFe₂ O₄ and NiFe₂ O₄ NPs. These quasi‐spherical particles of CoFe₂ O₄ and NiFe₂ O₄ were shown to have sizes in the range of 10–80 and 5–50 nm, respectively. The photocatalytic activity of metal ferrites was evaluated in H₂ O₂ assisted oxidative degradation of methylene blue (MB) and rhodamine B (RhB) under irradiation of solar light. Both metal ferrite photocatalysts exhibited pronounced activity in degradation of MB and RhB, respectively, but relatively higher activity was observed for NiFe₂ O₄. After completion, the catalysts were recovered using an external magnet. Recycling of these recovered catalysts up to five times showed no noticeable change in the efficiency.Inspec keywords: nanoparticles, nanofabrication, photochemistry, catalysts, cobalt compounds, nickel compounds, ferrites, X‐ray diffraction, transmission electron microscopy, Fourier transform infrared spectra, crystal structure, dyesOther keywords: Paederia foetida Linn, nanostructures, photocatalytic efficiency, cobalt ferrite nanoparticles, nickel ferrite nanoparticles, hydroxylating agent, leaf extract, bio‐template, powder X‐ray diffraction, transmission electron microscopy, Fourier transform‐infrared spectroscopy, vibrating sample magnetometer analysis, cubic face‐centred phase, quasi‐spherical particles, photocatalytic activity, methylene blue, rhodamine B, size 5 nm to 80 nm, CoFe₂ O₄ , NiFe₂ O₄      

Studies on the Properties of Manganese Substituted Nickel Ferrite Nanoparticles

Mn²⁺-substituted Ni ferrite nanoparticles were synthesized by sol-gel auto combustion method. The synthesized samples were annealed at 800 ^°C and characterization studies were carried out by XRD, VSM, electron paramagnetic resonance (EPR), field emission scanning electron microscopy (FE-SEM) and FT-IR spectroscopy. The XRD patterns revealed that Mn ²⁺-substituted Ni ferrite crystallizes in cubic spinel phase and addition of α-Fe ₂ O ₃ phase was also observed. The average crystallite sizes were found to be from 42 to 56 nm using a Scherer equation. The coercivity and remanent magnetization decreases when Mn ²⁺ ion concentration is increased. The EPR spectrum shows the phase homogeneity of the samples. The FE-SEM images revealed that particles are both spherical in shape and particle sizes varied from 22 to 41 nm. The FT-IR spectrum confirmed the two main metal ion vibrations of nickel ferrite near 550 to 560 cm ^?1 (A site) and 441 to 460 cm ^?1 (B site).     

Al2O3 reinforced Al/Ni intermetallic matrix composite by reactive sintering

An aluminium-nickel reinforced Al₂O₃ particulate composite was fabricated by a powder metallurgy route, where 35wt% aluminium and 30wt% nickel powders were mixed with 35wt% Al₂O₃ particles and compacted at 548 MPa. Sintering was carried out at 850 °C, where the synthesis reaction was sustained by the transient liquid phase resulting from the exothermic reaction associated with the formation of intermetallic compounds, i.e. reactive sintering. The resultant microstructure was studied using X-ray diffraction (XRD) and scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS). It was found that the initial distribution of individual constituent powders affect the outcome of the reactive sintering and that the inward diffusion of aluminium in nickel was responsible for nickel aluminide formation.     

A study of nanocrystalline NiFe2O4 in a silica matrix

The present work deals with the synthesis of nickel ferrite/SiO₂ nanocomposites, obtained by embedding nickel ferrite nanoparticles in a silica matrix, through sol-gel method based on hydrolysis and condensation of a silicon alkoxide and thermal treatment. Methods employed in characterization of the materials obtained at different ferrite concentration and at suitable thermal treatments were differential scanning calorimetry (DSC), X-ray diffraction (XRD), mid-infrared (IR) spectra and transmission electron microscopy (TEM). In purpose to evaluate magnetic properties of these nanocomposites, static magnetic measurements using vibrating sample magnetometer (VSM) were carried out.     

Physicochemical properties of fine-particle ZnFe<Subscript>2</Subscript>O<Subscript>4</Subscript> prepared by spray pyrolysis of nitrate solutions

Fine zinc ferrite (ZnFe₂O₄) powders uniform in morphology have been prepared by spray pyrolysis of nitrate solutions. Examination by scanning electron microscopy showed that the powders consisted of micron- and submicron-sized polycrystalline spherical particles. The ZnFe₂O₄ sample prepared by pyrolysis at 1000°C had paramagnetic properties. Its crystal structure was refined by the Rietveld method and was shown to be a partially inverse spinel with a degree of inversion near 15%. According to nitrogen adsorption measurements, the specific surface of the powders was 5.2 m²/g. The electrical conductance of a film produced from fine-particle zinc ferrite was found to be very sensitive to the hydrogen sulfide concentration in air.     

Synthesis of crystal MFe2O4 (M = Mg,Cu, Ni) microspheres

A low-temperature solvothermal synthetic method was developed for the large-scale synthesis of uniform-sized ferrite MFe₂O₄ (M = Mg, Cu, Ni) microspheres. The size of the as-prepared ferrite MFe₂O₄ microspheres could be controlled to be diameters 300–800 nm in diameter by adjusting some growth parameters, such as reaction time and concentration. The structures of the as-prepared ferrite MFe₂O₄ microspheres were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDAX). The magnetic properties of the ferrite MFe₂O₄ microspheres were also investigated.     

Synthesis and sintering of ZrO2-CeO2 powder by use of polymeric precursor based on Pechini process

Nanocrystalline ZrO₂-12 mol % CeO₂powders were synthesized using a polymeric precursor method based on the Pechini process. X-ray diffraction (XRD) patterns showed that the method was effective to synthesize tetragonal zirconia single-phase. The mean crystallite size attained ranges from 6 to 15 nm. The BET surface areas were relatively high reaching 97 m²/g. Studies by nitrogen adsorption/desorption on powders, dilatometry of the compacts, and transmission electron microscopy (TEM) of the powders, were also developed to verify the particles agglomeration state. Both citric acid : ethylene glycol ratio and calcination temperature affected the powder morphology, which influenced the sinterability and microstructure of the sintered material, as showed by scanning electron microscopy (SEM).     

Synthesis and magnetic properties of shuriken-like nickel nanoparticles

Shuriken-like nickel nanoparticles were successfully synthesized by a thermal decomposition method at 200 °C with Nickel(II) acetylacetonate (Ni(acac)₂) as the precursor and oleylamine (OAm) as the solvent and reductant, respectively. The phase structures, morphologies and sizes, and magnetic properties of the as-synthesized nickel products were characterized in detail by using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission-scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and vibrating sample magnetometer (VSM). Some key reaction parameters, such as the reaction time, reaction temperature and surfactants, have important influence on the morphology of the final products. XRD pattern indicated that the products are well-crystallized face-centered cubic (fcc) nickel phase. SEM images demonstrated that the nickel nanoparticles are shuriken-like morphology with average size around 150 nm. The mechanism of shuriken-like Ni nanoparticles (NPs) is proposed. The magnetic hysteresis loops of shuriken-like and spherical nickel products illustrated the ferromagnetic nature at 300 K, indicating its potential applications in magnetic storage.     

Hydrothermally-induced morphological transformation of GdVO4:Eu

The aim of the present study is to investigate the effect of a wide pH range on morphology and luminescence properties of europium-doped gadolinium vanadate (GdVO₄:Eu³⁺). GdVO₄:Eu³⁺ powders were hydrothermally synthesized at 180 °C for 24 h in a wide pH range. The as-synthesized powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and photoluminescence (PL) spectroscopy. The XRD results showed that GdVO₄:Eu³⁺ with the tetragonal structure formed at pH < 13 as a single phase and Gd(OH)₃ formed at pH ≥ 13 as a secondary phase. The SEM and TEM observations demonstrated the hydrothermally-induced morphological transformation of GdVO₄:Eu³⁺ powders by altering the pH of the synthesis solution. The possible mechanism for the morphological transformation was proposed. The intensities of the prominent peaks at 618 nm in the PL emission spectra of GdVO₄:Eu³⁺ powders considerably shift according to the specific morphology. The luminescence intensity of the octahedron- and rod-like GdVO₄:Eu³⁺ powders hydrothermally obtained at pH = 3 was the strongest one due to high packing density and high crystallinity as well as the extended reduction of the concentration of inherent defect states or adsorbed species.     

Controlled synthesis of blue spherical CoAl2O4 pigment powder in Pickering emulsion assisted with a hydrothermal process

A spherical blue CoAl₂O₄ pigment powder commonly used for coloring ceramic products has successfully been synthesized by co-precipitation of Co²⁺ and Al³⁺ ions in Pickering emulsion assisted with a hydrothermal process, and the formation mechanism of the as-prepared powder has briefly been discussed. The effects of pH condition on the crystalline phase and color tone of the pigment powder were investigated at 280?°C by varying the pH value of the reaction system. Then, under an optimized pH condition to produce blue, the pigment powder was synthesized still hydrothermally at different temperatures (210, 240, 270 and 300?°C) to assess the effect of hydrothermal reaction temperature on the pigment particle morphology. The resulting pigment powders were characterized by field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), CIELAB colorimetric analysis (CIE-L¹a¹b¹), laser particle size analysis (LPS), and N₂-adsorption measurement (BET). FE-SEM and TEM observations indicated that the pigment powders of spherical shape obviously were constructed by a core–shell double-layer structure, the radii of which all were ～150?nm or so with a shell of ～25?nm in thickness. XRD results demonstrated that the pigment powders that were obtained from the aforementioned method under a wide range of pH values invariably contained basically crystalline CoAl₂O₄ of high purity. CIE-L¹a¹b¹ data suggested that the pigment powders at 280?°C and pH?≤?11.2 appeared different chromas of bluish colors compared with that displaying black which was obtained at pH?=?12.3. LPS and BET results showed that the CoAl₂O₄ pigment powder prepared under the urea concentration of 3.6040?g for 24?h at the hydrothermal temperatures of 240?°C exhibited a narrow particle size distribution, the specific surface area of which was evaluated to be? ～56.4?m²/g.     

Study on thermodynamics and oxidation mechanism of ethylene glycol in the preparation of nanometer nickel powders

Nanometer nickel powders have been prepared using the polyol method with NaOH, Ni(NO₃)₂·6H₂O, ethylene glycol (EG), and polyvinylpyrrolidone (PVP) as raw materials. The thermodynamics of the reaction system was studied, and the E–pH diagram of Ni–EG–H₂O was plotted. The oxidation products of EG were predicted from the E–pH diagram, and CO₃²⁻ in alkaline solutions was identified as the product through the IR spectrum and CaCO₃ sediment. Field-emission scanning electron micrograph (FE-SEM) showed that spherical nanometer nickel powders were obtained.     

Influence of synthesis conditions on particle morphology of nanosized Cu/ZnO powder by polyol method

Cu/ZnO in nanosizes have been synthesized using ethylene glycol at various conditions. The effects of reaction temperature, extent of reduction, various precursors such as CuX₂·nH₂O, ZnX₂·nH₂O (X = Cl⁻, NO₃⁻, CH₃CO₂⁻), the addition of water and the removal of volatile compounds including water were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and dynamic light scattering (DLS). Cu/ZnO powders with an average diameter of as low as 50 nm was obtained with a very low polydispersity in the absence of a protective polymer. Ethylene glycol oxidation products were also identified by Fourier transform infrared (FTIR) spectroscopy. The morphology of Cu/ZnO powders and the yield of powders are found to be strongly dependent on the synthesis conditions.     

Magnetic properties of Ni-Zn ferrite powders formed by self-propagating high temperature synthesis reaction

The ferrite compositions of Ni_xZn_xFe₂O₄ were synthesized by self-propagating high temperature synthesis reaction with various contents of iron, iron oxide, nickel oxide and zinc oxide at oxygen partial pressures varying between 0.05 to 5.0 MPa. The oxygen pressure promoted the combustion reaction, while the compacting pressure retarded the reaction. The rate equation of ferrite formation is shown to be v = 14.5 exp (T_c1380 - 1) P _O2 ^0.2 . Phase identification of the final products by X-ray diffraction (XRD) revealed that the enhanced combustion reaction with oxygen pressure and iron content in the reactants resulted in increasing the spinel content in the combustion product. As the oxygen pressure changed from 0.1 to 5 MPa, the coercive force and residual magnetization decreased by about 73% and 66%, respectively, whereas, the maximum magnetization, susceptibility and Curie temperature increased by about 70%, 60%, and 32%, respectively. The improved magnetic properties are accounted for by the enhanced iron oxidation at a given combustion condition. Compared to the magnetic properties and productivity of the Ni-Zn ferrites prepared by wet chemical method, the self-propagating high temperature synthesis method at high oxygen pressure is one of the useful methods to fabricate improved ferrite powders.     

Thermal stability and phase formation of mechanically alloyed Ti-Al-Si-C powders

Two quarternary Ti-Al-Si-C powder mixtures, 55Ti-27Al-12Si-6C and 55Ti-36Al-6Si-3C, were mechanically alloyed. The as-alloyed and heated powders have been characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC). XRD patterns showed diffuse halos of amorphous like phase for 20-40 h milled powders, but TEM examinations demonstrated that the 40 h milled powders were mainly composed of Ti solid solutions, with some amount of amorphous phase. SEM observations displayed that the lamellar structures of Ti and Al formed at the early stage of milling process subsequently led to the formation of nano- or sub-micrometer particles of homogeneous composition after prolonged milling to 40 h. It is deduced that the solid-stated reaction by inter-diffusion of components should be responsible for phase formation during mechanical alloying. DSC curves of the 40 h milled powders exhibited two sharp exothermal peaks, and the investigation on thermal stability of the 40 h milled powders indicated that Ti₅Si₃ was first formed at lower temperature, followed by Al₂Ti₄C₂and TiC at intermediate temperature (820°C), and these phases were stable at elevated temperatures. These results raise the possibility of synthesizing TiAl-based composite with titanium silicides and titanium carbides as reinforcements by proper selection of powder compositions.     

Effects of calcination temperature on phase and microstructure evolution of BaTi4O9 powders

Calcining of the mixture of BaCO₃ and TiO₂ with a ratio 1:4 at different temperatures was carried out to synthesize BaTi₄O₉ powders. Phase evolution of the samples was studied using the differential thermal analysis (DTA) and X-ray diffractometry (XRD). Both techniques confirmed that the formation of BaTi₄O₉ started around 1000 °C. The XRD peaks showed that BaTi₄O₉ was most pronounced at 1250 °C. X-ray line broadening methods were employed to study the variation of particle size and microstrain of the BaTi₄O₉ powders. The Voigt function in a single line and the pseudo-Voigt function in the variance methods were used in our case. We found that both functions resulted in the same trends, i.e., the particle size increased with the temperature with the biggest size of 180 and 160 nm, whilst the microstrain yielded the opposite trend with the lowest values of 6.2 × 10^–3 and 1.1 × 10^–3. The scanning electron microscopy (SEM) study revealed the size of the large particles formed, due to agglomeration, to be about 0.5–1.9 μm. Furthermore, it was shown that irregular shapes of BaTi₄O₉ powders necked to each other appeared at 1000 °C and grew into ellipse and rod shapes at 1250 °C. Electronic Publication     

Catalytic Activity of the Spinel Ferrite Nanocrystals on the Growth of Carbon Nanotubes

We prepared three ferrite nanocatalysts: (i) copper ferrite (CuFe₂O₄) (ii) ferrite where cobalt was substituted by nickel (Ni _x Co_1?x Fe₂O₄, with x=0, 0.2, 0.4, 0.6), and (iii) ferrite where nickel was substituted by zinc (Zn _y Ni_1?y Fe₂O₄ with y=1, 0.7, 0.5, 0.3), by the sol-gel method. The X-ray diffraction patterns show that the ferrite samples have been crystallized in the cubic spinel structural phase. We obtained the size of grains by field emission scanning electron microscopy images and their magnetic properties by vibrating sample magnetometer. Next, carbon nanotubes were grown on these nanocatalysts by the catalytic chemical vapor deposition method. We show that the catalytic activity of these nanocrystals on the carbon nanotube growth depend on cation distributions in the octahedral and tetrahedral sites, structural isotropy, and catalytic activity due to cations. Our study may have applications in finding a suitable candidate of doped ferrite nanocrystals as catalysts for carbon nanotube growth. More interestingly, the yield of fabrication of carbon nanotubes can be considered as an indirect tool to study catalytic activity of ferrites.     

Self-assembly growth of BiFeO3 powders prepared by microwave-hydrothermal method

With FeCl₃·6H₂O and Bi(NO₃)₃·5H₂O powder as raw materials and KOH as a mineralizer, the pure phase BiFeO₃ (BFO) powder was synthesized by microwave-hydrothermal (MH) method at 200 °C, with the reaction time as little as 30 min. The range of preparing the BFO powders had been summarized. The field emission scanning electron microscopy (FE-SEM) images revealed that the little BFO plate grew together forming rock sugar-like BFO powders, and then they grew further to form the mussel-like BFO powders. The transmission electron microscope (TEM) images also improved the self-assembly growth of BFO powders. The X-ray diffraction (XRD), the high resolution transmission electron microscopy (HRTEM) and the selected area electron diffraction (SAED) results indicated that the BFO powders grew along the [110] and [104] crystal orientation. The B-H loops of BFO indicated that the weak magnetism existed in the pure phase BFO powders.     

A facile synthesis of ZnS nanocrystallites by pyrolysis of single molecule precursors,Zn (cinnamtscz)<Subscript>2</Subscript> and ZnCl<Subscript>2</Subscript> (cinnamtsczH)<Subscript>2</Subscript>

ZnS nanocrystallites were synthesised by pyrolysis method using Zn (cinnamtscz)₂ and ZnCl₂ (cinnamtsczH)₂ (cinnamtsczH = cinnamaldehyde thiosemicarbazone) as single source precursors. The prepared ZnS nanocrystallites were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction, UV-Vis and fluorescence spectroscopy. The peak broadening in XRD and emission at shorter wavelength in fluorescence spectra showed the presence of nanocrystallites. The blue shift in UV-Vis absorption spectroscopy also proved the formation of nanocrystallites. TEM images show presence of plate-like and spherical ZnS nanoparticles obtained from Zn(cinnamtscz)₂ and ZnCl₂ (cinnamtsczH)₂ respectively.