Selective synthesis of monoclinic and tetragonal phase LaVO<Subscript>4</Subscript> nanorods via oxides-hydrothermal route

Pure monoclinic (m-) and tetragonal (t-) LaVO₄ nanorods are successfully obtained via a facile oxides-hydrothermal method, in which V₂O₅ and La₂O₃ bulk powders are directly utilized as precursors without pretreatment. It is found that ethylenediamine tetraacetic disodium salt (EDTA) is a key factor for synthesizing t-LaVO₄. The as-obtained products are characterized by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and selected area electron diffraction (SAED). The FTIR spectra of VO₄ around 800 cm⁻¹ are suggested as an effective auxiliary means to identify the crystal phase of LaVO₄. UV–Visible spectra of LaVO₄ nanomaterials are obvious blue shift compared with the bulk m-LaVO₄ materials. The different photoluminescent properties of Eu³⁺ doped m- and t-LaVO₄ are demonstrated. A dissolution–precipitation mechanism is mainly responsible for the anisotropic morphology and phase control evolution of the LaVO₄ nanocrystals. The oxides-hydrothermal system is also applicable to prepare other pure LnVO₄ (Ln³⁺: Nd³⁺, Y³⁺, Sm³⁺) and doped LnVO₄ nanomaterials.     

Sonochemical synthesis of porous gold nano- and microparticles in a Rosette cell

We report the synthesis of Au nano- and microparticles that relies on α-D-glucose (C₆H₁₂O₆) as the reducer and stabilizer in a Rosette cell under 20 kHz ultrasound irradiation. The chemical and physical effects of ultrasonic irradiation on the synthesis were investigated. The results showed that an optimum pH is required for the formation of insoluble Au(0) particles. Upon irradiation, low pH yielded Au nanoparticles while high pH resulted in microparticles. The Au surface capping by α-D-glucose hydroxyl and carbonyl groups was confirmed by Fourier transform infrared (FT-IR) spectroscopy. X-ray diffraction (XRD) analysis indicated that the Au particles crystallize within the face-centered-cubic (FCC) cell lattice. Moreover, continuous sonication reduced larger amounts of the Au precursor compared to the intermittent mode. Furthermore, tuning sonication time and mode influences the particle size and porosity as characterized by scanning and transmission electron microscopy. Our results shed a new light into the importance of the experimental and ultrasound parameters in obtaining Au particles of desired features through sonochemistry.     

Magnetic properties of La-substituted NiFe2O4 via egg-white precursor route

Nano-sized NiFe_2−xLa_xO₄ ferrites (x=0.00, 0.01, 0.02, 0.03, 0.04, 0.5, 0.07 and 0.09) were synthesized for the first time by using metal nitrate and egg-white extract in aqueous medium. The ferrites were characterized by DTA-TG, XRD, TEM, FT-IR and VSM techniques. The thermal decomposition behavior revealed that the precursors were completely decomposed at about 420 °C. TEM image shows agglomerated nanoparticles with crystallite sizes agrees well with that estimated by XRD measurement. XRD patterns show a secondary phase of LaFeO₃ besides the cubic structure of the La-substituted ferrites. The lattice parameters, X-ray density and crystallite size were found to increase with the increasing La content. The VSM measurement exhibited a ferromagnetic property for all the samples at room temperature. With increasing La, M_s was found to decrease while H_c increased. The decrease in the saturation magnetization is attributed to the paramagnetic properties of lanthanum, which prefer to substitute iron present in the octahedral sites. The increase in the coercivity is due to either the stronger magnetocrystalline anisotropy induced by La substitution or the change in the crystallite size.     

On the role of lattice distortion in the catalytic properties of substituted orthovanadates La1−xFexVO4

A series of mixed orthovanadates with nominal compositions La_1−xFe_xVO₄ were synthesized and characterized using powder X-ray diffraction, Mössbauer spectroscopy and temperature-programmed reduction techniques. The substitution resulted in the co-presence of two distinct mixed metal compositions having either monoclinic LaVO₄ or a triclinic FeVO₄ structure. Both these constituent phases were however, found to be of distorted nature, with no measurable change in respective crystal symmetry. Furthermore, the extent of this distortion depended upon the value of x and is attributed to the partial substitutions at A-site, i.e. with a part of La by Fe in LaVO₄ lattice and a part of Fe by La in the FeVO₄ phase. The substitution-induced lattice distortion is found to result in the lowering of the reduction temperature in case of both the above mentioned phases, and also in the synergistic enhancement in catalytic activity for a model CO oxidation reaction.     

A novel approach for the synthesis of superparamagnetic Mn3O4 nanocrystals by ultrasonic bath

In this study, the synthesis of Mn₃O₄ (husmannite) nanoparticles was carried out in two different alkali media under sonication by ultrasonic bath and conventional method. Manganese acetate was used as precursor, sodium hydroxide and hexamethylenetetramine (HMT) as basic reagents in this synthesis. An ultrasonic bath with low intensity was used for the preparation of nanomaterials. The as prepared samples were characterized with X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (HRTEM, TEM), energy-dispersive spectrum (EDS), and superconducting quantum interference device (SQUID) analysis. The XRD patterns exhibit the nanocrystals are in pure tetragonal phase. The chemical composition was obtained by EDS analysis and confirmed the presence of Mn and O in the sample. According to the TEM and HRTEM results, both nanorods and nanoparticles of Mn₃O₄ were obtained in the presence of ultrasonic irradiation. The average size of nanoparticles was 10 nm, and the size of nanorods was 12 nm in diameter and 100-900 nm in length for the samples prepared in basic medium with sodium hydroxide. In the conventional method with the same basic medium, the nanorod was not observed and the nearly cubic nanoparticles was appeared with an average size of 2.5 nm. The selected area electron diffraction (SAED) patterns revealed that the nanocrystals are polycrystalline in nature. When HMT was used as a basic reagent in the presence of ultrasonic irradiation, it was led to a higher size of nanoparticles and nanorods than when sodium hydroxide was used as a basic reagent. The average size of nanoparticles was about 15 nm and its shape was nearly cubic. The diameter for nanorods was 50 nm and the length was about a few micrometers.The magnetic measurements were carried out on the sample prepared in sodium hydroxide under ultrasonic irradiation. These measurements as a function of temperature and field strength showed a reduction in ferrimagnetic temperature (T_c = 40 K) as compared to those reported for the bulk (T_c = 43 K). The superparamagnetic behavior was observed at room temperature with no saturation magnetization and hysteresis in the region of measured field strength.     

Aging of starting solutions for nanoparticles synthesis with two different ultrasonication

Novel concept of aging starting solutions for nanoparticle synthesis and the application of two different sonication to aging is introduced. In sonoprocess of nanoparticles from liquid phase, it is usual to irradiate ultrasound to a reacting solution during synthesis. In this work, ultrasound is applied to a starting solution before synthesis. In case of the SiO₂ sphere synthesis, the aging process elongated the induction period of the precipitation, enlarge the sphere size, and enhanced the monodispersity of silica spheres. These effects were promoted by soft sonication at subtle power (~1 mW). In case of the TiO₂ sphere case, ordinary (cavitating) ultrasound during synthesis was found to be effective in more spherical shape. Also, the sonication to aging of the starting solution was useful for uniform spheres synthesis. Existence of miscible liquid such as water-ethanol and feasible relationship to the nucleation of nanoparticles are discussed.     

Mechanochemically assisted synthesis of La0.7Sr0.3MnO3 nanoparticles and induction heating properties of the composites with hydroxyapatite

Perovskite lanthanum strontium manganese oxide (LSMO, strontium-substituted lanthanum manganite) La_0.7Sr_0.3MnO₃ nanoparticles were synthesized via the low-temperature calcination of the precursor, which was prepared using a mechanochemical route. A powder mixture of lanthanum chloride, strontium chloride, manganese chloride and sodium carbonate was high-energy milled by a planetary ball mill under semiwet (moist) conditions to obtain the precursor. To study the mechanochemical effects on the formation of LSMO, a thermogravimetric (TG) analysis was conducted for the precursors prepared under various conditions; the precursors and the intermediates formed during calcination were identified by X-ray diffraction (XRD). The calcination of the milled precursor at 600 °C resulted in the formation of LSMO nanoparticles with good induction heating properties. The LSMO/hydroxyapatite composites exhibited rapid temperature increases in an AC magnetic field. The obtained results demonstrate that the LSMO nanoparticles and LSMO/hydroxyapatite composites are promising candidates for magnetic hyperthermia treatments.     

Features of the doping effect on YAlO3 phase sequences during synthesis from an amorphous precursor state

Using X-ray diffraction methods, it has been shown that small lanthanum (La) dopants during solid-phase synthesis of YAlO₃ from an amorphous precursor state initiate the formation of the high-temperature hexagonal modification of yttrium aluminate in the first crystallization stages, whereas the equilibrium perovskite phase has an orthorhombic cell. At the same time, during YAlO₃ synthesis without dopants, yttrium-aluminum garnet Y₃Al₅O₁₂ is formed in the first crystallization stages, rather than the perovskite modification, as it follows from the precursor stoichiometry. The effect of lanthanum dopants on YAlO₃ phase sequences during synthesis from the amorphous precursor state is qualitatively explained.     

Synthesis and characterization of L10 FePt nanoparticles from Pt–Fe3O4 core-shell nanoparticles

Pt/Fe₃O₄ core-shell nanoparticles have been prepared by a modified polyol method. Pt nanoparticles were first prepared via the reduction of Pt(acac)₂ by polyethylene glycol-200 (PEG-200), and layers of iron oxide were subsequently deposited on the surface of Pt nanoparticles by the thermal decomposition of Fe(acac)₃. The nanoparticles were characterized by XRD and HR-TEM. The as-prepared Pt/Fe₃O₄ nanoparticles have a chemically disordered FCC structure and transformed into chemically ordered fct structure after annealing in reducing atmosphere (4% H₂, 96% Ar) at 700 °C. The ordered fct FePt phase has high magnetic anisotropy with coercivity reaching 7.5 kOe at room temperature and 9.3 kOe at 10 K.     

Sonochemical synthesis of Dy2(CO3)3 nanoparticles,Dy(OH)3 nanotubes and their conversion to Dy2O3 nanoparticles

Dysprosium carbonates nanoparticles were synthesized by the reaction of dysprosium acetate and NaHCO₃ by a sonochemical method. Dysprosium oxide nanoparticles with average size about 17 nm were prepared from calcination of Dy₂(CO₃)₃·1.7H₂O nanoparticles. Dy(OH)₃ nanotubes were synthesized by sonication of Dy(OAC)₃·6H₂O and N₂H₄. The as-synthesized nanostructures were characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FT-IR). Photoluminescence measurement shows that the nanoparticles have two emission peaks around 17,540 cm^?1 and 20,700 cm^?1, which should come from the electron transition from ⁴F_9/2 → ⁶H_15/2 levels and ⁴F_9/2 → ⁶H_13/2 levels, respectively. The effect of calcination temperature and sonication time was investigated on the morphology and particle size of the products. The sizes could be controlled by the feeding rate of the precipitating agent (NaHCO₃ and N₂H₄) and slower feeding rate lead to smaller nanoparticles.     

Sonochemical synthesis of cobalt aluminate nanoparticles under various preparation parameters

Cobalt aluminate (CoAl₂O₄) nanoparticles were synthesized using a precursor method with the aid of ultrasound irradiation under various preparation parameters. The effects of the preparation parameters, such as the sonochemical reaction time and temperature, precipitation agents, calcination temperature and time on the formation of CoAl₂O₄ were investigated. The precursor on heating yields nanosized CoAl₂O₄ particles and both these nanoparticles and the precursor were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM). The use of ultrasound irradiation during the homogeneous precipitation of the precursor reduces the duration of the precipitation reaction. The mechanism of the formation of cobalt aluminate was investigated by means of Fourier transformation infrared spectroscopy (FT-IR) and EDX (energy dispersive X-ray). The thermal decomposition process and kinetics of the precursor of nanosized CoAl₂O₄ were investigated by means of differential scanning calorimetry (DSC) and thermogravimetry (TG). The apparent activation energy (E) and the pre-exponential constant (A) were 304.26 kJ/mol and 6.441 × 10¹⁴ s^?1, respectively. Specific surface area was investigated by means of Brunauer Emmett Teller (BET) surface area measurements.     

Ultrasound mediation for one-pot sonosynthesis and deposition of magnetite nanoparticles on cotton/polyester fabric as a novel magnetic,photocatalytic, sonocatalytic,antibacterial and antifungal textile

A magnetic cotton/polyester fabric with photocatalytic, sonocatalytic, antibacterial and antifungal activities was successfully prepared through in-situ sonosynthesis method under ultrasound irradiation. The process involved the oxidation of Fe²⁺ to Fe³⁺ via hydroxyl radicals generated through bubbles collapse in ultrasonic bath. The treated samples were analyzed by X-ray diffraction, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy and vibrating sample magnetometry. Photocatalytic and sonocatalytic activities of magnetite treated fabrics were also evaluated toward Reactive Blue 2 decoloration under sunlight and ultrasound irradiation. Central composite design based on response surface methodology was applied to study the influence of iron precursor, pH and surfactant concentration to obtain appropriate amount for the best magnetism. Findings suggested the potential of one-pot sonochemical method to synthesize and fabricate Fe₃O₄ nanoparticles on cotton/polyester fabric possessing appropriate saturation magnetization, 95% antibacterial efficiency against Staphylococcus aureus and 99% antifungal effect against Candida albicans, 87% and 70% dye photocatalytic and sonocatalytic decoloration along with enhanced mechanical properties using only one iron rich precursor at low temperature.     

In situ sonosynthesis of nano TiO2 on cotton fabric

Here, titanium dioxide nanoparticles (NPs) were sonosynthesized and loaded simultaneously onto the cotton fabric. Titanium tetra isopropoxide (TTIP) was used as precursor and ultrasonic irradiation was utilized as a tool for synthesis of TiO₂ in low temperature with anatase structure and loading nanoparticles onto the cotton fabric. TiO₂ loaded cotton fabric was characterized by XRD, FE-SEM, EDS, and XRF. Moreover, several properties of the treated cotton fabrics such as self-cleaning, UV protection, washing durability, and tensile strength were studied. The effect of variables, including TTIP concentration and sonication time, was investigated based on central composite design (CCD) and response surface methodology (RSM). The results confirmed formation of anatase TiO₂ nanoparticles with 3–6 nm crystalline size loaded onto the cotton fabric at low temperature (75 °C) that led to good self-cleaning and UV-protection properties. The excellent UV-protection rating of the treated fabric maintained even after 25 home launderings indicating an excellent washing durability. Interestingly, sonochemical method had no negative influence on the cotton fabric structure. The statistical analysis indicated significant effect of both TTIP concentration and sonication time on the content of the loaded TiO₂ on the fiber and self-cleaning properties of the fabric.     

Reduced conductivity and enhancement of Debye orientational polarization in lanthanum doped cobalt ferrite nanoparticles

In this work we have investigated the conductivity and dielectric properties of CoLa_xFe_2−xO₄ (x=0.0, 0.03, 0.05, and 0.07) nanoparticles synthesized by chemical co-precipitation route. X-ray diffraction analysis confirms the inverse spinal structure of nanoparticles with slight increase in the lattice constant as La concentration increases. Transmission electron microscopy shows spherical nanoparticles with sizes of ∼20 nm. Impedance spectroscopy of the samples was performed in the frequency range 20 Hz-2 MHz at room temperature. The resistance of the grains and grain boundaries was found to increase with lanthanum concentration while the AC conductivity of the samples was observed to decrease with increasing La concentration. Dipolar orientational polarization was found to play an important role in determining dielectric properties of the samples.     

Influence of pH in La-doped SnO2 nanoparticles towards sensor applications

The present investigation has been carried out to optimize the pH level of lanthanum (La)-doped tin dioxide (SnO₂) nanoparticles towards the potential application in gas sensor. The La-doped SnO₂ nanoparticles were synthesized by sol-gel method in different pH values varying from acidic to base nature. The synthesized nanoparticles were characterized by X-ray diffraction (XRD), ultraviolet (UV), photoluminescence (PL), and scanning electron microscopy (SEM) techniques. The XRD, UV, and PL analyses show the pH influences on the crystallite size of La-doped SnO₂ nanoparticles. The SEM images show the formation of porous structure at pH 11. Also, the electrical conductivity of 1 mol% La-doped SnO₂ at pH 3 and pH 11 were measured by impedance analyzer. In addition, we have fabricated and demonstrated device performance of synthesized La-doped SnO₂ nanoparticles for gas-sensing application. Real-time current response and long-time response to the gas sensing were also studied for the fabricated device.

     

Preparation of superparamagnetic magnetite nanoparticles by reverse precipitation method: Contribution of sonochemically generated oxidants

Magnetic iron oxide nanoparticles were successfully prepared by a novel reverse precipitation method with the irradiation of ultrasound. TEM, XRD and SQUID analyses showed that the formed particles were magnetite (Fe₃O₄) with about 10 nm in their diameter. The magnetite nanoparticles exhibited superparamagnetism above 200 K, and the saturation magnetization was 32.8 emu/g at 300 K. The sizes and size distributions could be controlled by the feeding conditions of FeSO₄ · 7H₂O aqueous solution, and slower feeding rate and lower concentration lead to smaller and more uniform magnetite nanoparticles. The mechanisms of sonochemical oxidation were also discussed. The analyses of sonochemically produced oxidants in the presence of various gases suggested that besides sonochemically formed hydrogen peroxide, nitrite and nitrate ions contributed to Fe(II) ion oxidation.     

Features of LaBO3 phase formation during solid-phase synthesis from the amorphous precursor state

The features of the phase formation of pure lanthanum borate during solid-phase synthesis from an amorphous precursor state and from a homogenized mixture of initial oxide micropowders have been investigated using X-ray diffraction methods. It has been shown that LaBO₃ phase sequences obtained in both cases significantly differ from each other. The role of cross doping with Y, Sc, and La on the La_0.95Sc_0.05BO₃, La_0.95Y_0.05BO₃, Y_0.95La_0.05BO₃, and Sc_0.95La_0.05BO₃ phase sequence during synthesis from the amorphous precursor state has been clarified.     

Optical spectroscopy of Er-doped LaVO4 crystal

Transparent single crystals of erbium-doped LaVO₄ in form of platelets having an average size 0.5×2×2 mm³ were obtained by the flux method using Pb₂V₂O₇ as the solvent. Inductively coupled plasma (ICP) measurement revealed that the actual Er/La=0.3% molar ratio in the crystals is lower than Er/La=1% nominal molar ratio due to significant difference of ionic radii of La and Er. Luminescence spectra and luminescence decay curves for Er³⁺ transitions in the visible and near infrared region were recorded. Unpolarized Raman spectrum of undoped LaVO₄ crystal was acquired, too. Up-converted green emission following excitation at 808 and 970 nm was observed and dependence of its intensity on incident excitation power was determined. Based on experimental data gathered the relaxation dynamics of excited states of Er³⁺ was analyzed and mechanisms involved in the up-conversion phenomena were discussed.     

Control synthesis of magnetic Fe3O4–chitosan nanoparticles under UV irradiation in aqueous system

Novel magnetic Fe₃O₄–chitosan nanoparticles were synthesized via photochemical method in an emulsifier-free aqueous system at room temperature for the first time. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) results showed that the Fe₃O₄–chitosan nanoparticles were in regular shape with a mean diameter of 41 nm, whereas the average size in aqueous solution measured by photocorrelation spectroscopy (PCS) was 64 nm, which indicated that the nanoparticles had water-swelling properties. X-ray diffraction (XRD) patterns indicated that the Fe₃O₄ nanoparticles were pure Fe₃O₄ with a spinel structure, and the irradiation under UV light did not result in a phase change. The Fe₃O₄–chitosan nanoparticles were also characterized by Fourier transform infrared (FTIR) spectra, thermogravimetric analysis (TGA) and vibrating sample magnetometer (VSM). Magnetic measurement revealed that the saturated magnetization (Ms) of the Fe₃O₄–chitosan nanoparticles reached 48.6 emu/g and the nanoparticles showed the characteristics of superparamagnetism. The stability test showed these novel nanoparticles had high magnetic stability. The PCS and TGA results indicated that the size and chitosan content of Fe₃O₄–chitosan nanoparticles formed was pH- and chitosan/Fe₃O₄ ratio-dependent, which could be used to synthesize magnetic Fe₃O₄–chitosan nanoparticles with different size to meet the requirements of different applications.     

The suppression of structural phase transformation in LaVO3 and La1−xSrxVO3 thin films fabricated by pulsed laser deposition

Highly oriented (100) thin films of LaVO₃ and La_1−xSr_xVO₃ have been fabricated by pulsed laser deposition in a reducing atmosphere. The films show a transition from insulating to metallic behaviour in the composition region of x, 0.175<x<0.200. In the single crystals of the antiferromagnetic insulating phase, a first-order structural phase transition is observed few degrees below the magnetic transition, which manifests itself as a kink in the temperature dependence of resistivity. In the highly oriented thin films of LaVO₃ and La_1−xSr_xVO₃ fabricated on lattice matched substrates in this study, the structural phase transformation in the insulating phase has been suppressed. The electrical conduction is found to take place via hopping through localized states at low temperatures. The metallic compositions show a non-linear (T^1.5) behaviour in the temperature dependence of resistivity. V (2p) core level spectra of these films show a gradual change in the relative intensities of V³⁺ and V⁴⁺ ions as the value of x increases.