Sonochemical synthesis of carbon supported Sn nanoparticles and its electrochemical application

A sonochemical approach was employed to prepare Vulcan carbon XC-72R supported by Sn nanoparticles at room temperature in the presence of ethylene glycol. The reduction of metallic Sn ion and ethylene glycol takes place and in turn the glycolate ion as formed acts as a stabilizing agent. Transmission electron microscope, X-ray diffraction, and X-ray photoelectron spectroscopy have illustrated that the metallic Sn nanoparticles are successfully embedded on the carbon. The significantly observed reduction over potential for oxygen reduction reaction displays a higher catalytic activity of carbon supported by Sn nanoparticles due to the large surface area of the modified electrode.     

Sonochemical assisted synthesis of SrFe12O19 nanoparticles

We present the synthesis of M-type strontium hexaferrite by sonochemistry and annealing. The effects of the sonication time and thermal energy on the crystal structure and magnetic properties of the obtained powders are presented. Strontium hexagonal ferrite (SrFe₁₂O₁₉) was successfully prepared by the ultrasonic cavitation (sonochemistry) of a complexed polyol solution of metallic acetates and diethylene glycol. The obtained materials were subsequently annealed at temperatures from 300 to 900 °C. X-ray diffraction analysis shows that the sonochemical process yields an amorphous phase containing Fe³⁺, Fe²⁺ and Sr²⁺ ions. This amorphous phase transforms into an intermediate phase of maghemite (γ-Fe₂O₃) at 300 °C. At 500 °C, the intermediate species is converted to hematite (α-Fe₂O₃) by a topotactic transition. The final product of strontium hexaferrite (SrFe₁₂O₁₉) is generated at 800 °C. The obtained strontium hexaferrite shows a magnetization of 62.3 emu/g, which is consistent with pure hexaferrite obtained by other methods, and a coercivity of 6.25 kOe, which is higher than expected for this hexaferrite. The powder morphology is composed of aggregates of rounded particles with an average particle size of 60 nm.     

Sonochemical coating of magnetite nanoparticles with silica

Magnetite nanoparticles were coated with silica through the hydrolysis and condensation of tetraethyl orthosilicate (TEOS) under ultrasonic irradiation. The ultrasonic irradiation was used to prevent the agglomeration of the magnetite particles and accelerate the hydrolysis and condensation of TEOS. TEM, DLS, XRF, VSM, TG and sedimentation test were used to characterize the silica-coated magnetite particles. The dispersibility of silica-coated magnetite particles in aqueous solution was improved significantly and the agglomerate particle size was decreased to 110 nm. It was found that the agglomerate particle size of silica-coated magnetite particles was mainly decided by the coating temperature and the pH value in the silica-coating process. The weight ratio of silica in silica-coated magnetite particles was mainly decided by the pH value in the silica-coating process. The dispersibility of silica-coated magnetite particles was mainly decided by the agglomerate particle size of the suspension. The oxidation of magnetite particles in air was limited through the coated silica. The magnetism of silica-coated magnetite particles decreased slightly after silica-coating.     

Sonochemical synthesis,structural, magnetic and grain size dependent electrical properties of NdVO4 nanoparticles

NdVO₄ nanoparticles are successfully synthesized by efficient sonochemical method using two different structural directing agents like CTAB and P123. The phase formation and functional group analysis are carried out using X-ray diffraction (XRD) and fourier transform infra red (FT-IR) spectra, respectively. Using Scherrer equation the calculated grain sizes are 27 nm, 24 nm and 20 nm corresponding to NdVO₄ synthesized by without surfactant, with CTAB and P123, respectively. The TEM images revealed that the shape of NdVO₄ particles is rice-like and rod shaped particles while using CTAB and P123 as surfactants. The growth mechanism of NdVO₄ nanoparticles is elucidated with the aid of TEM analysis. From electrical analysis, the conductivity of NdVO₄ nanoparticles synthesized without surfactant showed a higher conductivity of 5.5703 × 10⁻⁶ S cm⁻¹. The conductivity of the material depends on grain size and increased with increase in grain size due to the grain size effect. The magnetic measurements indicated the paramagnetic behavior of NdVO₄ nanoparticles.     

Preparation and magnetic properties of magnetite nanoparticles by sol–gel method

 Magnetite (Fe₃O₄) nanoparticles have been successfully synthesized by sol–gel method combined with annealing under vacuum. The phase structures, morphologies, particle sizes, chemical composition, and magnetic properties of Fe₃O₄ nanoparticles have been characterized by X-ray diffraction, field emission scanning electron microscopy, energy-dispersive X-ray spectrometer and vibrating sample magnetometer (VSM). The results indicate that the size, the corresponding saturation magnetization value and coercivity value of Fe₃O₄ nanoparticles increase with the increase of synthesized temperature. And the phase transformation of Fe₃O₄ nanoparticles has been studied under different atmospheres and temperatures.     

Dependence of pH and surfactant effect in the synthesis of magnetite (Fe3O4) nanoparticles and its properties

Nanoparticles of Fe₃O₄ were synthesized by co-precipitation in an aqueous solution containing ferrous and ferric salts (1:2) at varying pH with ammonia as a base. It was found that the value of pH influences the reaction mechanism for the formation of Fe₃O₄. Furthermore, the addition of mercaptoethanol significantly reduced the crystalline size of Fe₃O₄ nanoparticles from 15.03 to 8.02 nm. X-ray diffraction (XRD) spectra revealed that the synthesized nanoparticles were ε-Fe₂O₃ or Fe₃O₄ phase. To further prove the composition of the product, as-prepared Fe₃O₄ were examined by X-ray photoelectron spectroscopy (XPS). Magnetic properties of the obtained particles were determined by vibrating sample magnetometer (VSM). Further analysis of the X-ray studies shows that while maintaining a pH value of 6 and 9 in a solution containing iron salts II and III ions produces ε-Fe₂O₃. Whereas a pH value of 11 produces magnetite (Fe₃O₄) phase. All of these results show that the pH has a major role in the observed phase formation of (Fe₃O₄) nanoparticles.     

Aqueous immune magnetite nanoparticles for immunoassay

Immune magnetite nanoparticles (MNPs) are prepared by four successive reactions, which are MNPs preparation, silica-coating, surface modification with amino group, and conjugation with bio-molecule, respectively. The crystal structure and morphology of intermediate products are characterized by XRD, TEM and AFM. Qualitative and quantitative assays for amino group on the MNPs’ surface are made by FTIR and Organic Element Assay. Ultraviolet–visible absorption spectrum can indirectly illustrate the quantity of bio-molecule conjugated with MNPs. In addition, specific combination and nonspecific combination of immune MNPs are measured by commercial RIA box. The results show that the size of MNPs prepared is 10 ± 5 nm, and silica-coated MNPs with spinel structure have quasi-spherical morphology. Infrared absorption bands of –NH₂ are appeared around 3380–3200 cm⁻¹ and 1650–1510 cm⁻¹, and the amino group content is 0.5 μmol –NH₂ per mg MNPs. The specific immune combination of immune MNPs is up to 75%, and nonspecific combination is under 5%.     

Microwave-assisted synthesis of magnetite nanoparticles for MR blood pool contrast agents

Microwave-assisted polyol process was developed for the synthesis of magnetite nanoparticles with precisely controlled size, high crystallinity and high water solubility. The process is simple, time-saving and low energy-consuming due to the advantages of polyols and microwave irradiation combined. The crystal phases of the nanoparticles were determined by transmission electron microscopy, X-ray powder diffraction and Raman spectrum. The coating materials of the nanoparticles were analyzed by Fourier transformed infrared spectroscopy and thermal gravimetric analysis. Precise size tuning enables an easier way to adjust the relaxation properties of the magnetite nanoparticles. The colloid nanoparticles with high longitudinal relaxivity (r₁) and low ratio of transverse relaxivity (r₂) to r₁ have a potential application in magnetic resonance angiography.     

Sonochemical synthesis, photocatalytic activity and optical properties of silica coated ZnO nanoparticles

In this paper, we report the synthesis of silica coated ZnO nanoparticles by ultrasound irradiation of a mixture of dispersion of ZnO, tetraethoxysilane (TEOS), and ammonia in an ethanol-water solution medium. The silica coating layer formed at the initial TEOS/ZnO loading of 0.8 for 60 min ultrasonic irradiation was uniform and extended up to 3 nm from the ZnO surface as revealed from HR-TEM images. Silica coated ZnO nanoparticles demonstrated a significant inhibition of photocatalytic activity against photodegradation of methylene blue dye in aqueous solution. The effects of silica coating on the UV blocking property of ZnO nanoparticles were also studied.     

EPR spectroscopy and imaging of TEMPO-labeled magnetite nanoparticles

The article presents results of a study of TEMPO-labeled polymer coated superparamagnetic iron(II,III) oxide nanoparticles using both Electron Paramagnetic Resonance (EPR) spectroscopy and Electron Paramagnetic Resonance imaging technique (EPRI). The X-band (9.4 GHz) EPR spectroscopy was used to investigate the behavior of TEMPO-labeled polymer coated magnetite nanoparticles in different conditions (temperature and orientation in magnetic field). The broad line, which comes from the core of Fe₃O₄ nanoparticles, shows anisotropy. This signal broadens with decreasing temperature, its intensity increases with increasing temperature and the g factor decreases with increasing temperature. The shape of the signal from nitroxide radical strongly depends on temperature. When temperature is higher than 200 K, a narrow triplet appears, but when it is lower than 200 K the signal consists of broad asymmetric lines. Analysis of the signal allowed characterization of the motion of the spin label attached to nanoparticles. Values of anisotropy parameter ɛ and rotational correlation time τ_c were calculated for TEMPO in the fast rotation regime.The ability of TEMPO-labeled PEG coated magnetite nanoparticles to diffuse within the hydrogel medium was also investigated. The EPR imaging of nanoparticles diffusion in hydrogel was made at room temperature using an EPR L-band (1 GHz) spectrometer. EPRI has been proved effective for evaluation of changes in the spatial distribution of nanoparticles in the sample.     

Sonochemical synthesis of Cu2O nanocubes for enhanced chemiluminescence applications

A facile one-step sonochemical synthesis of Cu₂O nanocubes has been developed by ultrasound irradiation of copper sulfate in the presence of polyvinylpyrrolidone and ascorbic acid at pH 11. During sonication, the reaction between acoustic cavitation-generated radicals and CuSO₄ produced Cu(OH)₂ intermediate which then reacted with ascorbic acid to generate Cu₂O nanocubes. The products were characterized by FT-IR, XRD, HRTEM, AFM and particle size analyzer. The prepared Cu₂O nanocubes were found to be very effective for enhancing chemiluminescence in the presence of luminol–H₂O₂ system.     

Sonochemical activation in aqueous medium for solid-state synthesis of BaTiO3 powders

BaTiO₃-based oxide compounds are important ceramic materials for multilayer ceramic capacitors. In this paper, we report a sonochemical activation process of BaCO₃ and TiO₂ in an aqueous medium for the synthesis of BaTiO₃ powders through a solid-state process. Owing to the physical and chemical effects of the ultrasonication in aqueous medium on the raw materials, BaTiO₃ powders could be successfully synthesized at relatively low temperatures through a solid-state reaction, which was significantly enhanced as compared to the case in ethanol medium. Detailed investigations on the resulting BaTiO₃ powders and ceramics were performed, and a model to understand the role of aqueous medium on the enhancement of the solid-state reaction was proposed in terms of Ba²⁺ ion leaching and zeta potential of TiO₂, which are strongly affected by the pH of the aqueous medium. Our results are not only helpful for cost-effective synthesis of BaTiO₃ through the highly reliable solid-state reaction process, but they also provide an understanding of the role of aqueous medium for the sonochemical process using raw materials with partial solubility in water.     

Anisotropy-induced quantum critical behavior of magnetite nanoparticles at low temperatures

The classical, thermally driven transition from ferrimagnets to superparamagnets in Fe₃O₄ nanoparticles can be converted into another quantum phase by a transverse microwave magnetic field or by a strong internal anisotropic field. These fields, perpendicular to the Ising axis, can destroy the magnetic long-range order to quantum paramagnets as the fields exceed some critical values. We have exploited the spin resonance spectrometer to determine the dynamic spin susceptibility and the critical exponent γ, which is a power-law dependent spanning of the quantum critical point. Quantum phase transition observed at low temperatures for small magnetite nanoparticles induced by strong surface anisotropic field illustrates the fascinating interplay between thermal and quantum fluctuations in the vicinity of a quantum critical point.     

Synthesis of magnetite nanoparticles for AC magnetic heating

Magnetite particles with different average diameter (D_m) suitable for magnetic fluid hyperthermia (MFH) were synthesized by controlled coprecipitation technique. In this method, the reaction pH was stabilized using the pH buffer and the average particle diameter decreased with increasing reaction pH. The size-dependent magnetic behavior of the magnetite nanoparticles was studied and the optimum size range required for magnetic fluid hyperthermia (MFH) has been arrived at. Among the samples studied, the maximum specific absorption rate of 15.7 W/g was recorded for the magnetite sample with D_m of 13 nm, when exposed to an AC magnetic field strength of 3.2 kA/m and a frequency of 600 kHz. The AC magnetic properties suggested that the size distribution of the sample was bimodal with average particle size less than ∼13 nm.     

Eu-doped ZnO nanoparticles: Sonochemical synthesis,characterization, and sonocatalytic application

Undoped and europium (III)-doped ZnO nanoparticles were prepared by a sonochemical method. The prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) analysis. The crystalline sizes of undoped and 3% Eu-doped ZnO were found to be 16.04 and 8.22 nm, respectively. The particle size of Eu-doped ZnO nanoparticles was much smaller than that of pure ZnO. The synthesized nanocatalysts were used for the sonocatalytic degradation of Acid Red 17. Among the Eu-doped ZnO catalysts, 3% Eu-doped ZnO nanoparticles showed the highest sonocatalytic activity. The effects of various parameters such as catalyst loading, initial dye concentration, pH, ultrasonic power, the effect of oxidizing agents, and the presence of anions were investigated. The produced intermediates of the sonocatalytic process were monitored by GC–Mass (GC–MS) spectrometry.     

Raman spectroscopy investigation of magnetite nanoparticles in ferrofluids

Raman spectroscopy is used to investigate magnetite nanoparticles dispersed in two types of β-cyclodextrin suspensions. An approach is presented for characterization of the magnetic core in liquid surrounding at room temperature and atmospheric pressure. The effect of elevating laser power on the structural stability and chemical composition of magnetite in the ferrofluids is discussed. The data are compared with data from dry by-products from the fluids. Powder samples undergo total phase transition from magnetite to hematite at laser power of 1.95 mW. The same nanoparticles in the fluid undergo transformation at 9 mW, but no hematite positions appear throughout that investigation. The Raman spectra revealed that the main phase of the magnetic core in the fluids is magnetite. That is indicated by a strong and non-diminishing in intensity peak at 670 cm⁻¹. A second phase is present at the nanoparticle’s surface with Raman spectroscopy unveiling maghemite-like and small fractions of goethite-like structures. The Fourier transform infrared spectroscopy investigations confirm deviations in the surface structure and also point to the fact that the oxidation process starts at an early stage after formation of the nanoparticles. The analyses of the infrared data also show that β-cyclodextrin molecules retain their cyclic character and the coating does not affect the oxidation process once the particles are evicted from the fluids. A Mössbauer spectroscopy measurement on a ferrofluidic sample is also presented.     

Sonochemical synthesis of LiNi0.5Mn1.5O4 and its electrochemical performance as a cathode material for 5 V Li-ion batteries

LiNi_0.5Mn_1.5O₄ was synthesized as a cathode material for Li-ion batteries by a sonochemical reaction followed by annealing, and was characterized by XRD, SEM, HRTEM and Raman spectroscopy in conjunction with electrochemical measurements. Two samples were prepared by a sonochemical process, one without using glucose (sample-S1) and another with glucose (sample-S2). An initial discharge specific capacity of 130 mA h g⁻¹ is obtained for LiNi_0.5Mn_1.5O₄ at a relatively slow rate of C/10 in galvanostatic charge–discharge cycling. The capacity retention upon 50 cycles at this rate was around 95.4% and 98.9% for sample-S1 and sample-S2, respectively, at 30 °C.     

Sonochemical fabrication of inorganic nanoparticles for applications in catalysis

Catalysis covers almost all the chemical reactions or processes aiming for many applications. Sonochemistry has emerged in designing and developing the synthesis of nano-structured materials, and the latest progress mainly focuses on the synthetic strategies, product properties as well as catalytic applications. This current review simply presents the sonochemical effects under ultrasound irradiation, roughly describes the ultrasound-synthesized inorganic nano-materials, and highlights the sonochemistry applications in the inorganics-based catalysis processes including reduction, oxidation, degradation, polymerization, etc. Or all in all, the review hopes to provide an integrated understanding of sonochemistry, emphasize the great significance of ultrasound-assisted synthesis in structured materials as a unique strategy, and broaden the updated applications of ultrasound irradiation in the catalysis fields.     

Synthesis of magnetite nanoparticles via a solvent-free thermal decomposition route

Superparamagnetic nanoparticles have been widely applied in various bio-medical applications. To date, it is still a challenge to synthesize nanosized Fe₃O₄ particles with controlled size and distribution. In this paper, a novel solvent-free thermal decomposition method is reported for synthesizing Fe₃O₄ nanoparticles. Size and morphology of the nanoparticles are determined by TEM while the structure of the nanoparticles is identified by FTIR, XPS and TGA measurements. Magnetic properties of the obtained particles are determined using VSM and SQUID measurement. The particle size of the Fe₃O₄ can be tailored by adjusting either reaction temperature or time. When the reaction temperature is increased to 330 °C and the reaction time is extended to 4 h, the average particle size of the obtained nanoparticles is ∼9 nm, while Ms value reaches ∼76 emu/g. The as synthesized Fe₃O₄ nanoparticles show well-established superparamagnetic properties with the blocking temperature at around 100 K.