Influence of synthesis conditions on structural,optical and magnetic properties of iron oxide nanoparticles prepared by hydrothermal method

The iron oxide nanoparticles were synthesized by a simple hydrothermal method at different heating temperatures and pH conditions. The synthesized materials were characterized by X-ray diffractometer, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, UV–visible spectrometer and vibrating sample magnetometer. With increment in pH of the synthesized materials were resulted in orthorhombic (goethite) and cubic (magnetite) structures at pH 6 and 12, respectively. The banding nature of synthesized materials was analyzed by infrared spectra. The synthesized powders at 130?°C showed higher percent of nanorods (length = 90–120 nm) in addition to lower percentage of nanoparticles. The material at pH 12 consisted of maximum nanoparticles with size = 10–60 nm with small agglomerations. Band gap energy of synthesized materials was 2.2–2.8 eV. Herein, the reaction conditions tuned the saturation magnetization (M_S). The maximum M_S (59.38 emu/g) was obtained at pH 12 and lower M_S (0.65 emu/g) was observed at pH 6 due to intrinsic property of goethite phase.     

Nanostructured microspheres of silver @ zinc oxide: an excellent impeder of bacterial growth and biofilm

Au@TiO₂ core–shell hollow nanoparticles were prepared by a simple hydrothermal method without surfactants or templates. The core–shell structure materials were characterized by transmission electron microscopy, X-ray powder diffraction, scanning electron microscopy, and specific surface area of the test (BET). The catalytic activity was tested in a stainless reactor with a fixed bed and connected with a gas chromatograph. The results show that the microstructure, crystallography, and morphology were correlated with the hydrothermal reaction time and temperature, and the properties of the solvent. The crystallinity degree of TiO₂ and the particle size increased with the reaction time and temperature. Particles with different morphologies can be obtained when using different solvents. The size of microsphere can be controlled easily by changing the amount of TiF₄. This material exhibited the complete CO conversion temperature to be about 130 °C and no deactivation was observed after 1,000 min reaction.     

Oxygen reduction at sol–gel derived La0.8Sr0.2Co0.8Fe0.2O3 cathodes

The perovskite material, La_0.8Sr_0.2Co_0.8Fe_0.2O₃ (LSCF), substituted by Sr and Fe at the A and B sites, was prepared using the sol–gel (SG) method, followed by heating at 900 °C for 4 h. The X-ray powder diffraction pattern for the SG derived LSCF material showed good agreement with the literature data. Scanning electron microscopy showed that the LSCF structure is highly porous, facilitating gas transfer and maximizing the number of active sites for the oxygen reduction reaction (ORR) at the cathode of a solid oxide fuel cell. Transmission electron microscopy (TEM) was employed to determine the SG–LSCF particle size and distribution. The kinetics of the ORR were investigated at SG–LSCF, deposited by screen-printing on a samarium-doped ceria (SDC) electrolyte, using electrochemical impedance spectroscopy and cyclic voltammetry at temperatures ranging from 400 to 700 °C. The results showed that the SG–LSCF cathode is stable and exhibits a high exchange current density (and low charge transfer resistance), yielding an apparent activation energy for the ORR of ca. 120 kJ/mol. It was also found that the SG–LSCF on SDC cathode was approximately one order of magnitude more active than standard manganite-based composite cathodes, deposited on yttria stabilized zirconia, studied under otherwise identical operating conditions.     

Investigation of structural and electrical properties of NdFeO3 perovskite nanocrystalline

The permittivity, impedance and AC conductivity studies of NdFeO₃ perovskite nanocrystalline material were performed in the frequency range 1 kHz–100 kHz, and temperature range 100 K–320 K. The Sol–gel auto-combustion technique employed to synthesis NdFeO₃ perovskite compound. The X-ray diffraction (XRD) pattern of NdFeO₃ indicating the single-phase orthorhombic structure. The Scanning electron microscopy (SEM) image shows that the grains homogeneously spread throughout the surface morphology. The average grain size found to be 50 nm. The P–E loop suggests that the NdFeO₃ material is ferroelectric in nature. An impedance spectroscopy study suggests that the negative temperature coefficient of resistance (NTCR) behavior of the material. The conductivity spectrum follows the Jonscher's law.     

Titania Gold Composite: Effect of Illumination on Size of Gold Nanoparticles with Consequent Implication on Photocatalytic Water Splitting

This work deals with the study of photodeposition (PD) of gold nanoparticles (AuNPs) on TiO₂ by using different illumination sources, Medium pressure Mercury lamp (ML), Solar Simulator equipped with AM 1.5 (SL) and Tungsten lamp (WL). Different particle size of AuNPs on TiO₂ were obtained by photodeposition method under different illumination sources, which clearly proves the influence of light source on the synthesis of Au–TiO₂. The plasmonic activity of Au–TiO₂ photocatalyst for water splitting reaction was observed to be strongly influenced by the particle size of Au as well as illumination source. Amongst the three different illumination sources used, smallest particle size for AuNP–TiO₂ were observed under ML followed by SL and WL, as revealed by TEM analysis. Different illumination sources were also investigated to evaluate the activity of Au–TiO₂ samples thus prepared under different illumination conditions. The order of hydrogen evolution rate (HER) observed for Au–TiO₂ with different source of illuminations is ML > SL > WL. The highest HER of 1709 μmol/h was observed for Au–TiO₂, which was synthesized and evaluated under ML irradiation. This may be explained on the basis of reduced catalytic activity and photothermal effect of Au nanoparticles with increasing particle size.     

Raman and IR studies of BaBi2Ta2O9 prepared by a sol–gel process

The formation of ferroelectric BaBi₂Ta₂O₉ (BBT) by a sol–gel process was studied by X‐ray, Raman and infrared (IR) spectroscopy. Our results show that the formation of a Bi‐layered phase proceeds via an intermediate fluorite‐type phase. This method allows obtaining a BBT phase already at 750 °C. This temperature is about 150–200 °C lower than that required in the conventional solid‐state reaction. Therefore, a material with smaller particle size can be obtained. Raman and IR studies of the obtained Bi‐layered phase show that phonon properties of the synthesized particles are slightly different from those of the bulk material due to the size effect, defects and weak changes in local order. Temperature dependence of Raman and IR wavenumbers is consistent with the orthorhombic distortion of the BBT structure. Copyright © 2011 John Wiley & Sons, Ltd.     

Hydrothermal synthesis of LiMnO2 microcubes for lithium ion battery application

Two kinds of LiMnO₂ microcubes were successfully synthesized by hydrothermal method using solid or hollow Mn₂O₃ microcubes as precursors. One was made up of nanoparticles varying in size and the other was made up of interlaced polygonal nanoplates with the thickness of 70 nm. Both kinds of LiMnO₂ microcubes were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Charge–discharge curves were carried out to investigate their electrochemical properties. LiMnO₂ microcubes with interlaced nanoplates showed much better capacities than the ones with nanoparticles indicating it is more suitable for application in the lithium ion batteries. The former material could deliver the capacities of 197 and 134 mAh/g at 0.1 and 1 C, respectively. And its capacity fading after 50 cycles did not exceed 7 %. The excellent electrochemical performance of the former material could be ascribed to the smaller size which could shorten the path length for lithium ion transport and increase the electrode and electrolyte contact.     

Effect of thickness on the structural,optical and electrical properties of thermally evaporated PbI2 thin films

This work describes the physical properties of lead iodide (PbI₂) thin films with different thicknesses that were deposited on ultrasonically cleaned glass substrates using a thermal evaporation technique at 5×10^-6 torr. The initial material was purified by the zone refining technique under an atmosphere of argon gas. XRD analysis of the material demonstrates that the thin films were preferably oriented along the (001) direction. The size of the crystallites was calculated from the Scherer relation and found to be in the range of ～5–10 nm, with higher values being observed for increasing film thicknesses. The optical energy band gaps were evaluated and determined to belong to direct transitions. Because the band gap increased with decreasing film thickness, a systematic blue shift was observed. The surface morphologies of PbI₂ films exhibited a clear increase in grain size with increasing film thickness. The photoluminescence and dc conductivity of the thin films are also discussed.     

Microwave-assisted synthesis of Zn–WO3 and ZnWO4 for pseudocapacitor applications

Nanosized Zn–WO₃ and ZnWO₄ materials have been prepared by microwave irradiation method. The physico-chemical characterization of the prepared nanomaterials was carried out by X-ray diffraction (XRD) and high resolution-scanning electron microscopy (HR-SEM) techniques. The size and shape of the ZnWO₄ material can be controlled by changing the temperature. The XRD analysis revealed the formation of monoclinic phase of the calcined nanopowder. The HR-SEM images showed the sphere and plate shape particles. The electrochemical behavior of the ZnWO₄ modified electrodes was investigated using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD) techniques. The synthesized material shows the pseudocapacitance. The specific capacitance of 35.70 F/g was achieved for the Zn–WO₃ nanopowder.     

Elaboration and characterization of bimetallic nanoparticles obtained by laser ablation of Ni75Pd25 and Au75Ag25 targets in water

A YAG laser operating at the second harmonic wavelength (532 nm, 10 Hz, 8 ns and 40 mJ) was used to elaborate bimetallic nanoparticles by laser ablation of Ni₇₅Pd₂₅ and Au₇₅Ag₂₅ targets in water. TEM–EDX, UV–Vis spectroscopy and PIXE measurements were performed to obtain information on their mean sizes, size distributions and chemical composition as a function of the time of laser ablation. The surface of the laser impacted regions of the targets were characterized by RBS in order to check their composition after the laser ablation. The so-obtained bimetallic nanoparticles always show a homogeneous composition. However, while the composition of Au–Ag nanoparticles was found to be very similar to the one of the alloy target, the composition of the Ni–Pd nanoparticles can be different from the nominal composition of the alloy target. Segregation phenomena can be invoked to explain the difference between the Ni–Pd nanoparticles and the Au–Ag nanoparticles compositions obtained in the same conditions. However, an influence of chemical reactions occurring in the high pressure plasma created locally at liquid–solid interface (called ‘reactive quenching’) cannot be completely ruled out.     

Structural and optical tunability of metallodielectric composites with gradual shell growth

Metallodielectric (gold@silica) composites were prepared by seed and grow method. The dielectric microspheres (core material) of an average size of 400 nm were synthesized by sol–gel method and gold nanoparticles (AuNPs) were prepared by reducing the chloroauric solution. Shell growth around silica (SiO₂) microspheres was carried out in a multistep layer-by-layer process. The synthesized composites were characterized using techniques such as field emission-scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and UV–Visible (UV–Vis) spectroscopy. FE-SEM and FTIR analyses have confirmed the functionalization of SiO₂ surfaces with the amine terminal group along with the gold shell growth. XRD analysis has given an average crystallite size of 12.3 nm for metallodielectric composites. Absorption spectra have demonstrated the dependence of surface plasmon resonance (SPR) peak on the successive shell growth by exhibiting a red shift.     

Co-precipitation of asiatic acid and poly(<Emphasis Type="SmallCaps">l</Emphasis>-lactide) using rapid expansion of subcritical solutions into liquid solvents

Poly(l-lactide) (PLLA) nanoparticles loaded with asiatic acid (AA) were successfully produced by rapid expansion of a subcritical solution into an aqueous receiving solution containing a dispersing agent. A mixture of carbon dioxide (CO₂) and ethanol (EtOH) with a weight ratio of 1:1 was used as the solvent for AA and PLLA. Two surfactants, Pluronic F127 and sodium dodecyl sulfate were employed. The former was found to be more effective for stabilizing AA-loaded PLLA nanoparticles, as a rapid expansion into a 0.1 wt% Pluronic F127 solution produced a stable nanosuspension consisting mainly of well-dispersed, individual nanoparticles. The effects of rapid expansion-processing conditions—AA to PLLA weight ratio and pre-expansion temperature (T_pre)—on the size and morphology of composite nanoparticles, and the loading capacity and entrapment efficiency of AA in PLLA nanoparticles, were systematically investigated. It was found that AA-loaded PLLA nanoparticles with a size range of 30–100 nm were consistently fabricated by rapid expansion at T_pre of 70–100 °C and AA to PLLA weight ratios of 1:2 and 1:4, and with a constant pre-expansion pressure of 330 bar. The T_pre and AA to PLLA weight ratio had no significant effects on the size of the nanoparticles. The AA to PLLA weight ratio is a controlling parameter for both the loading capacity and the entrapment efficiency of AA in PLLA nanoparticles. The loading capacity and entrapment efficiency increased from 8–11 to 16–21 wt%, and 38–57 to 50–62 wt%, respectively, when the AA to PLLA weight ratio changed from 1:4 to 1:2. However, increasing the T_pre from 70 to 100 °C decreased both the loading capacity and entrapment efficiency of AA in PLLA nanoparticles by ~20–30%.     

Highly sensitive ethanol sensors based on nanocrystalline SnO2 thin films

This paper reports on a simple and inexpensive ultrasonic spray pyrolysis method to synthesize agglomerate-free nanosized SnO₂ particles with a size smaller than 10 nm. Scanning electron microscopy, transmission electron microscopy and high resolution X-ray diffraction studies were used to characterize the morphology, crystallinity, and structure of the SnO₂ particles. Under the optimized experimental conditions, the prepared SnO₂ sensor shows the high response (S = 491) towards 100 ppm ethanol gas at 300 °C, linearity in the range of 100–500 ppm, quick response time (2 s), recovery time (60 s) and selectivity against other gases. The response of the sensor was monitored in a 250–450 °C temperature range. The seven fold enhancement in gas response and selective detection of C₂H₅OH in the presence of other gases such as CH₃OH and CH₃CHOHCH₃ are the significant points in this investigation. These results demonstrate that pure nanocrystalline SnO₂ thin film can be used as the sensing material for fabricating high performance ethanol sensors.     

Influence of sintering temperature and pH on the phase transformation,particle size and anti-reflective properties of RHA nano silica powders

Nano silica powders were synthesized from rice husk ash, the most silica-rich raw material, using alkaline extraction followed by acid precipitation. The phase transformation during sintering, the influence of sintering temperature and pH on the particle size and anti-reflective properties of nano silica were investigated. The results showed that the amorphous SiO₂ sintered at 600°C were transformed to a cristobalite structures completely during the sintering process at 800°C and 1100°C. With the increasing sintering temperature and pH, the particle size distributions (d₅₀) were increased respectively in the range of 62–84, 192–240, and 283–329?nm at sintering temperatures of 600°C, 800°C, and 1100°C. When the sintering temperatures were increased at 1100°C, 98.15% and 96.84% of transmittances were obtained respectively at the highest and lowest points of the anti-reflection band and could be used for anti-reflective applications.     

Triblock copolymer-templated synthesis of porous TiO2 and its photocatalytic activity

Mixed amorphous and anatase-type titania particles were synthesized using non-ionic triblock copolymer as surfactant template and TiOSO₄ as inorganic precursor through sol–gel process. The as-prepared materials were characterized by X-ray diffraction spectroscopy, scanning and transmission electron microscopy, specific surface area, Fourier-transformed infrared spectroscopy, and diffuse reflectance ultraviolet–visible spectroscopy. The template material could be easily removed by extracting with dichloromethane and was confirmed by infrared spectroscopy. X-ray diffraction pattern reveals the crystalline part of as-prepared product as a framework of anatase phase. From the N₂ adsorption–desorption analysis, the as-prepared sample has a surface area of 301 m²/g with pore size distribution narrowly centered around 6 nm. The photodegradation of indigo carmine including kinetics, effect of pH, and recyclability of the product were investigated. The photocatalytic results showed that the as-synthesized titania could efficiently degrade indigo carmine under ultraviolet irradiation and showed higher photocatalytic activity than the commercial Degussa P25–TiO₂.     

Multilayered Materials Comprising Mesoporous Thin Films and Metal Nanoparticles

A novel composite material based on metal nanoparticles (NP) and mesoporous thin films (MPTF), more specifically bilayers of MPTF with a submonolayer of NP deposited between them is introduced. By controlling the deposition conditions, it is possible to build a variety of multilayers including MPTF with different compositions (TiO₂, SiO₂) and pore sizes (templated with cetyltrimethylammonium bromide, F127, Brij 58) and NP of different characteristics and sizes (Au spheres, Au decorated SiO₂). By means of 2D small angle X‐ray scattering, transmission electron microscopy, UV–vis spectroscopy, and ellipsometric porosimetry it is demonstrated that NP and MPTF retain their structure and properties within the new material. Importantly, the NP remain accessible for further reactions, a feature that is established by Au overgrowth. Interestingly, the extent of Au growth depends on the mesoporous size and the position of the MPTF with respect to the NP. This new architecture allows the NP to be in direct contact with two different chemical environments and, as a consequence, opens up the possibility to control identity and size of the molecules that can reach them. Thus, the obtained materials may be applied in the development of highly specific sensors and catalysts, in which spatial position plays a fundamental role.     

Effects of atomization conditions on morphology and SOFC anode performance of spray pyrolyzed NiO–Sm0.2Ce0.8O1.9 composite particles

NiO–Sm_0.2Ce_0.8O_1.9 (NiO–SDC) composite particles were synthesized by spray pyrolysis (SP). SP resulted in composite particles of NiO enveloped with SDC and these capsule-type composite particles would reduce aggregation of Ni during the reduction from NiO to Ni metals. SOFC anode microstructures and morphologies of NiO–SDC composite precursor particles much affects on SOFC power densities or anode polarization. Therefore, we focused on atomizing conditions of SP process. Relationship between ultrasonic atomization conditions and morphologies of NiO–SDC composites were investigated by controlling temperatures of atomization vessels. The atomizing temperature changed concentration of mists in the vessel, and mean particle size and particle size distribution were increased with an increase in temperature of the atomization vessels. Some extremely large particles were observed by synthesizing at higher atomization temperatures. Large particles contained voids in the particles. The voids in the composite particles would play a role of pore-formers. SOFC measurement showed the synthesis at the atomizing temperature of 30 °C resulted in the high-performance anode. The atomizing process of SP much affected morphology of anode precursor particles, and the atomizing conditions were important to improve anode performance.     

Synthesis of copper-nickel nanoparticles prepared by mechanical milling for use in magnetic hyperthermia

Mechanical alloying of a mixture of copper and nickel powders has been applied for the preparation of copper-nickel alloy particles in the nanometer range. The particles were designed to be used for controlled magnetic hyperthermia applications. The milling conditions were optimized using the desired alloy composition. Utilizing a ball-to-powder mass ratio of 20, we could obtain a nanocrystalline Cu_27.5Ni_72.5 (at%) alloy with a crystallite size of around 10 nm and a Curie temperature of 45 °C.Thermal demagnetization in the vicinity of the Curie temperature of the nanoparticles was determined by thermomagnetic measurements using an adapted TGA-SDTA apparatus. The size and morphology of the particles were determined by XRD measurements and TEM analyses. The magnetic properties were also examined with a VSM. The magnetic heating effects were measured for the powdered material.     

Failure analysis of magnets in a servomotor by Mössbauer and X-ray diffraction

The failure of a servo motor with Nd–Fe–B magnets under harsh atmospheric conditions is analysed. The magnets presented corrosion both on the side glued to the rotor (magnet-bottom) and on the opposite side (magnet-top), and eventually came off the rotor shaft. The corrosion products were studied by X-ray diffraction and Mössbauer spectroscopy and compared to the uncorroded magnet material. The observed products, Nd(OH)₃ and iron oxyhydroxides, evolve from the magnet-bottom to the top, and show that the atmospheric environment was wet with a high concentration of salts. Finally, some paramagnetic powder was found away from the magnet set, as a consequence of rotor rotation, and it represents a further oxidation process of the magnet products. The surface protection of the magnets has shown to be insufficient for the atmospheric working conditions.