A simple approach for the synthesis of Co<Subscript>3</Subscript>O<Subscript>4</Subscript> nanocrystals

By using Co²⁺ and Co³⁺ salts, and freshly extracted ovalbumin, Co₃O₄ nanocrystals have been synthesized successfully. The pH of the solution was self-regulated for the hydrolysis of metal ions as the ovalbumin-water mixture was highly basic. Water soluble ovalbumin proteins served as a perfect matrix for entrapment of Co²⁺ and Co³⁺ ions thus forming a gel. Upon heat treatment, the dried gel precursor decomposed into nanocrystalline Co₃O₄. The crystallite size obtained by XRD line profile fitting was 45 ± 8 nm and particle size estimated from the SEM was in the range 20 nm-2 μm. EPR results show a very good fit to literature reports for nanocrystals in the size range of 8–17 nm. Even though the overall particle size is quite large and its distribution is quite wide EPR results confirm nanocrystalline nature of the particles obtained. Presented route is simple, cost effective, and environmentally friendly.     

Solventless synthesis of m-LaVO<Subscript>4</Subscript> photocatalyst for the degradation of methylene blue and textile effluent

Lanthanum vanadate (LaVO₄) nanoplates with monoclinic (m) phase were synthesized by a facile solventless method. Lanthanum nitrate and ammonium metavanadate was used as precursors in this method. X-ray diffraction pattern reveals the monoclinic phase of LaVO₄ (m-LaVO₄). In addition, average grain size and lattice parameters were also calculated. Fourier transform infrared (FT-IR) analysis confirms the presence of La–O and V–O bonds in the sample. Optical property of m-LaVO₄ nanoplates was estimated by DRS UV–visible and photoluminescence spectroscopy. HR-TEM (high resolution-transmission electron microscopy) analysis predicts the formation of LaVO₄ nanoplates. Furthermore, m-LaVO₄ nanoparticles were utilized as photocatalyst for the photodegradation of methylene blue (MB) dye under visible light illumination. m-LaVO₄ photocatalyst showed substantial efficiency for the photodegradation of textile effluent (TE) within 120 min of visible light irradiation.     

Structural,electrical and magnetic properties of Mn<Subscript>3</Subscript>O<Subscript>4</Subscript>/MgO nanocomposite

The present paper deals with the synthesis of Mn₃O₄/MgO nanocomposite through a simple sol–gel route and their electrical and magnetic properties are discussed for electrode applications. The grain size and particle morphology of the synthesized nanocomposite are characterized using XRD and HRSEM. The elemental compositions of the synthesized samples were analyzed using EDAX spectra. The dielectric constant, dielectric loss and AC conductivity of the synthesized samples were studied in the frequency range of 100 Hz–5 MHz at different temperatures (303–573 K) using impedance spectra. The activation energy was calculated using Arrhenius plot. The vibrating sample magnetometry (VSM) study shows that the nanocomposites are found to be paramagnetic at room temperature.     

Synthesis of magnetic Cu/CuFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanocomposite as a highly efficient Fenton-like catalyst for methylene blue degradation

A magnetic Cu/CuFe₂O₄ nanocomposite was synthesized by a facile one-pot solvothermal method and characterized as an excellent Fenton-like catalyst for methylene blue (MB) degradation. The content of zero-valent copper (Cu⁰) in Cu/CuFe₂O₄ composite could be simply controlled by changing the dosage of sodium acetate in the synthetic process, and the Fenton-like catalytic performance of Cu/CuFe₂O₄ composite enhanced with increasing the Cu⁰ content. In the presence of H₂O₂ (15 mM), the as-synthesized 3-Cu/CuFe₂O₄ nanocomposite could remove 99% of MB (50 mg/L) after only 4 min at pH 2.50, greatly higher than that of pure CuFe₂O₄ and Cu⁰ under the same condition. The enhancement activity of Cu/CuFe₂O₄ nanocomposite was due to the synergistic effect between Cu⁰ and CuFe₂O₄. The radical capture experiments and coumarin fluorescent probe technique confirmed that MB was degraded mainly by the attack of OH^· radicals in Cu/CuFe₂O₄–H₂O₂ system.     

Visible photocatalytic degradation of methylene blue on magnetic semiconducting La<Subscript>0.2</Subscript>Sr<Subscript>0.7</Subscript>Fe<Subscript>12</Subscript>O<Subscript>19</Subscript>

Methylene blue (MB) is a representative of a class of dyestuffs resistant to biodegradation. This paper presents a novel photocatalytic degradation of MB by La_0.2Sr_0.7Fe₁₂O₁₉ compound, which is a traditional permanent magnet and displays a large magnetic hysteresis (M–H) loop. The remnant magnetic moment and coercive field are determined to be 52 emu/g and 5876 Oe, respectively. UV–Visible optical spectroscopy reveals that La_0.2Sr_0.7Fe₁₂O₁₉ is simultaneously a semiconductor, whose direct and indirect band gap energies are determined to be 1.47 and 0.88 eV, respectively. The near infrared band gap makes it a good candidate to harvest sunlight for photocatalytic reaction or solar cell devices. This magnetic compound demonstrates excellent photocatalytic activity on degradation of MB under visible illumination. The colour of MB dispersion solution changes from deep blue to pale white and the absorbance decreases rapidly from 1.8 down to zero when the illumination duration extends to 6 h. Five absorption bands did not make any blue shifts along with the reaction time, suggesting a one-stepwise degradation process of MB, which makes La_0.2Sr_0.7Fe₁₂O₁₉ a unique magnetic catalyst and differs from TiO₂ and other conventional catalysts.     

Facile synthesis,characterization and BET study of neodymium-doped spinel Mn<Subscript>3</Subscript>O<Subscript>4</Subscript> nanomaterial with enhanced photocatalytic activity

In this study, bare Mn₃O₄ and Neodymium (Nd)-doped Mn₃O₄ were prepared via a facile hydrothermal strategy. These materials were characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, UV spectroscopy, X-ray photoelectron spectroscopy, and the Brunauer–Emmett–Teller (BET) method. XRD pattern displays that the particles were well crystallized and corresponds to a spinel structure of Mn₃O₄. The BET specific surface area and pore volume of mesoporous Mn₃O₄ greatly exceeds that of Nd-doped Mn₃O₄ samples. The sonophotocatalytic activity of Nd-doped Mn₃O₄ nanoparticles was evaluated by monitoring the decolorization of Reactive Red 43 in aqueous solution under sono-photocatalytic process. 4% Nd-doped Mn₃O₄ nanoparticles showed the highest decolorization efficiency among the different amounts of dopant agent used. The Nd-doped Mn₃O₄ could be a promising candidate material for high-capacity, low-cost, and environmentally friendly catalyst for wastewater remediation.     

A facile two-step hydrothermal route for the synthesis of γ-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocrystals and their magnetic properties

This paper proposes a facile two-step hydrothermal route for the synthesis of maghemite (γ-Fe₂O₃) nanocrystals. The synthesis route included two steps: (i) hydrothermal synthesis of Fe₃O₄ nanocrystals, and (ii) hydrothermal oxidation of the Fe₃O₄ nanocrystals to their γ-Fe₂O₃ counterpart. Phase transition from γ-Fe₂O₃ to hematite was studied by in situ XRD; the γ-Fe₂O₃ nanocrystals exhibited enhanced phase transition temperature (>600 °C). The magnetization curves revealed that the γ-Fe₂O₃ nanocrystals showed ferromagnetic behavior with high saturation magnetization of 68 emu/g at room temperature.     

Nano-domain structure of Li<Subscript>4</Subscript>Mn<Subscript>5</Subscript>O<Subscript>12</Subscript> spinel

XRD-pure Li₄Mn₅O₁₂ spinels are obtained below 600 °C from oxalate and acetate precursors. The morphology consists of nanometric particles (about 25 nm) with a narrow particle size distribution. HRTEM and electron paramagnetic resonance (EPR) spectroscopy of Mn⁴⁺ are employed for local structure analysis. The HRTEM images recorded on nano-domains in Li₄Mn₅O₁₂ reveal its complex structure. HRTEM shows one-dimensional structure images, which are compatible with the (111) plane of the cubic spinel structure and the (001) plane of monoclinic Li₂MnO₃. For Li₄Mn₅O₁₂ compositions annealed between 400 and 800 °C, EPR spectroscopy shows the appearance of two types of Mn⁴⁺ ions having different metal environments: (i) Mn⁴⁺ ions surrounded by Li⁺ and Mn⁴⁺ and (ii) Mn⁴⁺ ions in Mn⁴⁺-rich environment. The composition of the Li⁺, Mn⁴⁺-shell around Mn⁴⁺ mimics the local environment of Mn⁴⁺ in monoclinic Li₂MnO₃, while the Mn⁴⁺-rich environment is related with that of the spinel phase. The structure of XRD-pure Li₄Mn₅O₁₂ comprises nano-domains with a Li₂MnO₃-like and a Li_4/3−x Mn_5/3+x O₄ composition rather than a single spinel phase with Li in tetrahedral and Li_1/3Mn_5/3 in octahedral spinel sites. The annealing of Li₄Mn₅O₁₂ at temperature higher than 600 °C leads to its decomposition into monoclinic Li₂MnO₃ and spinel Li_4/3−x Mn_5/3+x O₄.     

Preparation and electrochemical behavior of methylene blue intercalated into layered niobate K<Subscript>4</Subscript>Nb<Subscript>6</Subscript>O<Subscript>17</Subscript>

K₄Nb₆O₁₇ nano-layered compound was obtained by solid-phase synthesis and then methylene blue (MB) was intercalated into layered niobate K₄Nb₆O₁₇ interlayer I by a two-step guest-guest exchange method using the intercalation compound, methyl viologen (MV²⁺)–K₄Nb₆O₁₇, as precursor. The optically transparent MB⁺–K₄Nb₆O₁₇ nanocomposite thin film has been characterized by XRD, IR, TGA, elemental analysis, UV, and electrochemical measurements. It was estimated that the intercalated MB⁺ ions are mainly aggregated. The cyclic voltammogram of the MB⁺–K₄Nb₆O₁₇ nanocomposite thin film exhibited a fine diffusion-controlled cathodic process, which hints the possibility of being utilized as an electrode modifying material.     

An efficientfficient,controllable and facile two-step synthesis strategy: Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@RGO composites with various Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles and their supercapacitance properties

An efficient,controllable,and facile two-step synthetic strategy to prepare graphene-based nanocomposites is proposed.A series of Fe3O4-decorated reduced graphene oxide (Fe3O4@RGO) nanocomposites incorporating Fe3O4 nanocrystals of various sizes were prepared by an ethanothermal method using graphene oxide (GO) and monodisperse Fe3O4 nanocrystals with diameters ranging from 4 to 10 nm.The morphologies and microstructures of the as-prepared composites were characterized by X-ray diffraction,Raman spectroscopy,nitrogen adsorption measurements,and transmission electron microscopy.The results show that GO can be reduced to graphene during the ethanothermal process,and that the Fe3O4 nanocrystals are well dispersed on the graphene sheets generated in the process.The analysis of the electrochemical properties of the Fe3O4@RGO materials shows that nanocomposites prepared with Fe3O4 nanocrystals of different sizes exhibit different electrochemical performances.Among all samples,Fe3O4@RGO prepared with Fe3O4 nanocrystals of 6 nm diameter possessed the highest specific capacitance of 481 F/g at 1 A/g,highlighting the excellent capability of this material.This work illustrates a promising route to develop graphene-based nanocomposite materials with a wide range of potential applications.     

Mn<Subscript>3</Subscript>O<Subscript>4</Subscript>/worm-like mesoporous carbon synthesized via a microwave method for supercapacitors

A quick and facile microwave method has been employed to prepare Mn₃O₄/worm-like mesoporous carbon (Mn₃O₄–MC) composites. Structural and morphological characterizations of worm-like mesoporous carbon and Mn₃O₄–MC composites have been carried out using X-ray diffraction, transmission electron microscopy, N₂ adsorption–desorption, and electrochemical measurement. Cyclic voltammograms demonstrate that the Mn₃O₄–MC composites perform improved capacitive behavior at the range of −0.8~0.2 V (vs. Hg/HgO electrode) with reversibility. The Mn₃O₄–MC composite electrode possesses an enhanced specific capacitance of 266 F g⁻¹ at a sweep rate of 1 mV s⁻¹.     

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.     

Fast microwave synthesis of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> and Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/Ag magnetic nanoparticles using Fe<Superscript>2+</Superscript> as precursor

A simple and quick microwave method to prepare high performance magnetite nanoparticles (Fe₃O₄ NPs) directly from Fe has been developed. The as-prepared Fe₃O₄ NPs product was fully characterized by X-ray diffraction, transmission electron microscopy and scanning electron microscopy. The results show that the as-prepared Fe₃O₄ NPs are quite monodisperse with an average core size of 80 × 5 nm. The microwave synthesis technique can be easily modified to prepare Fe₃O₄/Ag NPs and these NPs possess good magnetic properties. The formation mechanisms of the NPs are also discussed. Our proposed synthesis procedure is quick and simple, and shows potential for large-scale production and applications for catalysis and biomedical/biological uses.     

Photocatalytic degradation of methylene blue by C<Subscript>3</Subscript>N<Subscript>4</Subscript>/ZnO: the effect of the melamine/ZnO ratios

The C₃N₄/ZnO composite photocatalysts were synthesized by mechanical milling combined with a calcination process. Various ratios of melamine and ZnO powders were milled by a planetary ball mill for 10 h. After heating at 540^°C for 3 h in air, melamine was converted to C₃N₄ but the formation of C₃N₄ depended on the ratios of the melamine and ZnO (M/Z) powders. From the experimental results, the conversion of melamine to C₃N₄ could be inhibited by ZnO particles; as there was no detectable C₃N₄ in the sample at low M/Z values or high ZnO contents. The photocatalytic activities of prepared samples were investigated under the illumination of blacklight and fluorescent lamps as the low wattage light source. The C₃N₄ /ZnO showed a better photocatalytic activity than ZnO to degrade a methylene blue (MB) dye solution using blacklight lamps, but there is no significant difference in photocatalytic activities between ZnO and prepared C₃N₄/ZnO under visible light by the fluorescent lamps. However, the prepared C₃N₄/ZnO can well function under illumination by Xe lamp as the high power light source. Ecotoxicities of MB solutions before and after photocatalytic process were also studied through growth inhibition of the alga Chlorella vulgaris.     

Synthesis and thermoluminescence properties of CdB<Subscript>4</Subscript>O<Subscript>7</Subscript>:Tb<Superscript>3+</Superscript> and CdB<Subscript>4</Subscript>O<Subscript>7</Subscript>:Mn<Superscript>2+</Superscript>

Polycrystalline samples of undoped, terbium-doped (CdB₄O₇:Tb³⁺), and manganese-doped (CdB₄O₇:Mn²⁺) cadmium tetraborate have been prepared by solid-state reactions at 850°C. Using differential scanning calorimetry and X-ray diffraction, we have determined the melting point of CdB₄O₇ (t _m = 976°C) and shown that this compound melts incongruently. The observed monotonic decrease in the orthorhombic cell parameters of the doped materials indicates the formation of substitutional solid solutions (sp. gr. Pbca). The thermoluminescence intensity of the doped materials has been shown to depend on the nature and concentration of the activators and the irradiation time.     

Microwave synthesis and sintering characteristics of CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript>

CaCu₃Ti₄O₁₂ (CCTO) was synthesized and sintered by microwave processing at 2·45 GHz, 1·1 kW. The optimum calcination temperature using microwave heating was determined to be 950°C for 20 min to obtain cubic CCTO powders. The microwave processed powders were sintered to 94% density at 1000°C/60 min. The microstructural studies carried out on these ceramics revealed the grain size to be in the range 1–7 μm. The dielectric constants for the microwave sintered (1000°C/60 min) ceramics were found to vary from 11000–7700 in the 100 Hz–00 kHz frequency range. Interestingly the dielectric loss had lower values than those sintered by conventional sintering routes and decreases with increase in frequency.     

Solvothermal synthesis and characterization of size-controlled monodisperse Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles

Monodisperse Fe₃O₄ nanoparticles with narrow size distribution could be successfully synthesized in large quantities by a facile solvothermal synthetic method in the presence of oleic acid and oleylamine. Well-defined assembly of uniform nanoparticles with average sizes of 8 nm can be obtained without a further size-selection process. The sizes of final products could be readily tuned from 5 to 12 nm by adjusting the experimental parameters such as reaction time, temperature, and surfactants. The phase structures, morphologies, and magnetic properties of the as-prepared products were investigated in detail by X-ray diffraction, transmission electron microscopy, selected area electron diffraction, high-resolution transmission electron microscopy, and magnetometry with a superconducting quantum interference device. The magnetic study reveals that the as-synthesized nanoparticles are ferromagnetic at 2 K while they are superparamagnetic at 300 K.     

Electrical properties of Ni<Subscript>0.93</Subscript>Co<Subscript>0.02</Subscript>Mn<Subscript>0.05</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> + BaTiO<Subscript>3</Subscript> ME composites

Polycrystalline samples of mixed composites of Ni_0.93Co_0.02Mn_0.05Fe₂O₄ + BaTiO₃ were prepared by conventional double sintering ceramic method. The phase analysis was carried out by using X-ray diffraction technique. Variation of dc resistivity and thermo emf was studied as a function of temperature. AC conductivity (σ_ac) was investigated in the frequency range 100 Hz–1 MHz. The loss tangent (tan δ) measurements conclude that the conduction mechanism in these samples is due to small polaron hopping. The magnetoelectric conversion factor, i.e. dc(ME) _H was studied as a function of intensity of magnetic field and the maximum value 407 μV/cm/Oe was observed at a field of 0.8 kOe in a composite with 85% BaTiO₃ and 15% Ni_0.93Co_0.02Mn_0.05Fe₂O₄ phase.     

Magnetic properties of Er<Subscript>2</Subscript>Mn<Subscript>2/3</Subscript>Re<Subscript>4/3</Subscript>O<Subscript>7</Subscript>, a new zirkelite-structure oxide

We have studied the magnetic properties of the new compound Er₂Mn_2/3Re_4/3O₇ prepared by reacting Er₃ReO₈, ReO₂, MnO, and metallic Re at 1020°C in silica tubes sealed off under vacuum. The compound is shown to have the zirkelite structure with hexagonal cell parameters a = 7.3174(6) Å and c = 17.365(1) Å (sp. gr. P3₁21₁, Z = 6). Magnetization data obtained in the range 2–300 K demonstrate that, above ～150 K, its magnetic susceptibility exhibits Curie-Weiss behavior with an effective magnetic moment of 9.50μ_B. Dynamic magnetic susceptibility measurements point to spin-glass behavior of this compound at low temperatures.