Room temperature formation of ammonia by oxidizing hydrogenated cerium nanoparticles in the air

Ammonia formation was observed when hydrogenated cerium nanoparticles prepared by hydrogen plasma-metal reaction (HPMR) were exposed to the air at room temperature. This novel phenomenon represents a successful example of room temperature cleavage of dinitrogen and may find application in low temperature synthesis of ammonia under thermodynamically favorable conditions. A possible mechanism is also proposed. We suggest that the oxidation of cerium hydride offers chemical force to drive the hydrogen atoms out of the lattice. The monoatomic H released to the surface is highly active and readily reacts with N2 to yield ammonia. Some surface processes, which we know little about at the moment, are likely to be involved so as to lower the energy barrier of nitrogen dissociation. Further investigation is required to elucidate the detailed mechanism.     

Structural and optical studies of yttrium oxide nanoparticles synthesized by co-precipitation method

Yttrium oxide (yttria) nanoparticles were successfully synthesized by co-precipitation method. As-synthesized and annealed powders were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscope (SEM), UV-visible (UV-vis), photoluminescence (PL) spectra and Fourier transform infrared spectrometer (FTIR). The XRD results show that the as-prepared sample has mixed phase of Y(OH)₃ and yttria (Y₂O₃). However, cubic yttrium oxide phase alone is found for annealed samples. The strain values are calculated from Williamson-Hall (W-H) plot for annealed samples. SEM and TEM micrographs show that the samples are composed of aggregated nanoparticles with different shapes and sizes. From the UV-vis spectra, it is found that the position of the absorption peak is shifted towards the lower wavelength side when particle size decreases. In the PL spectra, the broad emission bands are observed between 340 and 380 nm and the presence of metal oxide is confirmed by FTIR spectra.     

Hydrothermal synthesis and formation mechanism of hexagonal yttrium hydroxide fluoride nanobundles

This article presents the fabrication of hexagonal yttrium hydroxide fluoride nanobundles via one-pot hydrothermal process, using yttrium nitrate, sodium hydroxide and ammonia fluoride as raw materials to react in propanetriol solvent. The X-ray diffraction pattern clearly reveals that the grown product is pure yttrium hydroxide fluoride, namely Y(OH)_2.02F_0.98. The morphology and microstructure of the synthesized product is testified to be nanobundles composed of numerous oriented-attached nanoparticles as observed from the field emission scanning electron microscopy (FESEM). The chemical composition was analyzed by the energy dispersive spectrum (EDS), confirming the phase transformation of the products which was clearly consistent with the result of XRD analysis. It is proposed that the growth of yttrium hydroxide fluoride nanobundles be attributed to ion exchange and precipitation transformation.     

Insight of yttrium doping on the structural and dielectric characteristics of ZnO nanoparticles

We report on synthesizing rare-earth yttrium oxide-doped ZnO nanoparticles through high-energy planetary milling approach. The impact of varying dopant content in the 3.0, 5.0 to 7.0 wt% range on microstructural, optical and electrical properties of ZnO nanoparticles has been successfully explored. The XRD data showed the existence of a hexagonal wurtzite ZnO phase along with Y₂O₃ impurity peaks, and the SEM micrographs divulge the development of semi-spherical nanoparticles. The incorporation of Y₂O₃ dopant in ZnO lattice has been supported by EDS, XPS and Raman analysis. The frequency and composition dependence of dielectric parameters was investigated and interpreted according to the Maxwell Wagner model. The data revealed non-monotonic dependence of the dielectric constant (ε_r), dielectric loss (tan δ) and AC conductivity and impedance of ZnO with varying dopant content. The variation of the shape of the impedance semicircles and the equivalent circuits between pure and doped ZnO samples prove increased grain boundary resistance due to Y₂O₃ incorporation. The study reveals that Yttrium-doped ZnO nanostructures are possible potential candidates for application in electronic devices if the dopant’s content is controlled.

     

Phase formation in yttrium aluminum garnet powders synthesized by chemical methods

Yttrium aluminum garnet (YAG) powders were synthesized by precipitation of hydroxides using three types of precursors: nitrates (nitrate process), isopropoxides (alkoxide process), and isopropoxides chelated with ethyl acetoacetate (modified alkoxide process). The phase development in the powders during heat treatments was investigated with DTA and XRD. An intermediate hexagonal YAlO₃ (YAH) phase was formed at 800°C in all powders regardless of the synthesis processes, but its complete transformation to YAG at higher temperatures (1000°C) occurred only in the powders prepared by the nitrate and modified alkoxide processes. The alkoxide process led to the largest deviation from the bulk composition, producing a single phase of YAH that transformed into YAG plus a stable YAM (Y₄Al₂O₉) phase. The modified alkoxide process led to the most homogeneous bulk composition, resulting in the least amount of YAH in the powder. The poor chemical homogeneity in the powders prepared by the nitrate and alkoxide processes was attributed to the segregation of the hydroxides and to the presence of the double alkoxide, respectively.     

The influence of methane/argon plasma composition on the formation of the hydrogenated amorphous carbon films

The quality of the a-C:H films was particularly correlated with the mixed ratio of methane/argon plasma. For a constant supply of energy and flowing rate, the optical emission from H_α intensity linearly increased with the addition of methane in argon plasma, while that from intensities of radiation of diatmoic radicals (CH^?and C₂^?) exponentially decreased. For the a-C:H films, the added methane in argon plasma tended to raise the quantity of hydrogenated carbon or sp³ C-H structure, which exponentially decreased the nano-hardness and friction coefficient of the films. In contrast, the electric resistance of the films enlarged dramatically with the increase of the methane content in argon plasma. It is therefore advantageous to balance the mechanical properties and electrical resistance of the a-C:H film by adjusting plasma composition in the course of the film-growing process.     

Formation and thermal stability of aluminium nanoparticles synthesized via yttrium ion implantation into sapphire

Yttrium ion implantation of 1 1 2 3 alumina resulted in the formation of metallic aluminium–yttrium, face centred cubic (a0=0.41 nm) spherical nanocrystals ( 12 nm in diameter) embedded in an amorphous matrix. A fluence of 5×1016Y+/cm2 implanted at ambient temperature and accelerating energies of 150 or 170 keV yielded this result. Crystalline nanoparticles were not present in the amorphous matrix for implantations done with identical conditions but lower energy (100 keV). Substrates implanted at 150 keV were annealed in laboratory air for times ranging from 20 to 90 min and temperatures ranging from 1000 to 1400°C. A clear progression of morphologies resulted from these annealing treatments. A 1000°C, 90 min anneal produced 13% recrystallization of the amorphous region and induced the formation of crystallites of a metastable Y–Al alloy. An 1100°C, 90 min anneal demonstrated 40% recrystallization of the amorphous region, accompanied by the formation of partially aligned internal grains of Y2O3. Electron diffraction shows that the Y–Al alloy crystallites which formed in the 1000°C anneal are also present at 1100°C. A highest temperature anneal of 1400°C, 60 min induced essentially complete recrystallization of the amorphous phase, the dissolution of the metastable Y–Al alloy, the retention of the internal yttria grains, and the formation of partially oriented external grains of yttria resulting from the segregation of yttrium to the substrate surface.     

Synthesis and characterization of pyrochlore-type yttrium titanate nanoparticles by modified sol–gel method

Pyrochlore-type yttrium titanate (Y₂Ti₂O₇) nanoparticles were successfully synthesized by a simple soft-chemistry technique viz. citric acid sol–gel method (CAM). The preparation process was monitored by X-ray diffraction, thermogravimetric–differential thermal analysis and Fourier transform–infrared experiments and the microstructures and average size of as-prepared products were characterized by transmission electron microscopy and high resolution transmission electron microscopy images. It was found that compared with traditional solid state reaction (SSR), Y₂Ti₂O₇ nanopowders were synthesized at a relatively low temperature (750°C) for shortened reaction time. Detailed analysis showed that the as-prepared Y₂Ti₂O₇ with good dispersibility and narrow size distribution were quasi-spherical; the average size was about 20–30 nm, also, the obtained products had higher BET surface area (50 m²/g). These properties are very helpful for a photocatalyst to achieve excellent activity and may result in better behaviour in hydrogen storage.     

Improvement of medical applicability of hydroxyapatite/graphene oxide nanocomposites via additional yttrium oxide nanoparticles

Hydroxyapatite is one of the most studied bioactive materials in the biomedical field. However, Hydroxyapatite’s low mechanical strength and low fracture toughness represent a limitation in its applications as a load-bearing biomaterial. Yttrium oxide and graphene oxide (GO) have previously been shown to enhance these mechanical characterization of hydroxyapatite (HAP) when combined in binary nanocomposites. In this study, a novel ternary nanocomposite hydroxyapatite/yttrium oxide/graphene oxide has been developed and its characteristics have been compared to the nanoparticles and binary nanocomposites of its components. The compositions of the prepared materials have been confirmed. The typical morphologies of the three components of the nanocomposites have been shown by scanning and transmission electron microscopes with HAP nanoparticles. The average roughness has decreased from 11.4 nm in the nanoparticles of the pure HAP to 7.9 nm in the ternary nanocomposite. All prepared nanocomposites have shown an acceptable slight decrease in cell viability with 96.9 ± 3.5% cell viability in the composite. The ternary nanocomposite has also shown a higher antibacterial activity compared to its individual constituents, with a zone of inhibition of 12.9 ± 1.1 mm and 12.5 ± 0.9 mm against E. coli and S. aureus, respectively, compared to no inhibition in the case of pure Hydroxyapatite.     

Misfit layer formation in icosahedral nanoparticles

We have studied the mechanism of internal stress relaxation in icosahedral pentagonal nanoparticles (PNPs), which is related to the formation of a crystal lattice mismatched layer. The optimum misfit parameter is determined, for which the energy gain as a result of this relaxation is maximum. It is shown that the threshold radii of icosahedral PNPs for some fcc metals, at which the formation of a misfit layer becomes energetically favorable, are on the order of ∼10 nm.     

The formation of magnetite nanoparticles on the sidewalls of multi-walled carbon nanotubes

Linear polyethyleneimine (PEI) was used as a non-covalent functionalizing agent to modify multi-walled carbon nanotubes (MWCNTs). Fe₃O₄ nanoparticles were then formed along the sidewalls of the as-modified MWCNTs through a simple solvothermal method. X-ray diffraction, Fourier transform infrared spectrometry, transmission electron microscopy, and vibrating sample magnetometry were used to characterize the MWCNT/Fe₃O₄ nanocomposites. Results indicated that Fe₃O₄ nanoparticles with diameters ranging from 50 to 200 nm were attached to the surface of the MWCNTs by electrostatic interaction. PEI was found to improve the electrical conductivity of the MWCNT/Fe₃O₄ nanocomposites. The magnetic saturation value of these magnetic nanocomposites was 61.8 emu g⁻¹. These magnetic MWCNT/Fe₃O₄ nanocomposites are expected to have wide applications in bionanoscience and technology.     

Sunlight-driving formation and characterization of size-controlled gold nanoparticles

Exposing a sodium citrate-HAuCl4 aqueous solution to sunlight results in the formation of size-controlled, citrate-capped gold nanoparticles. The gold nanoparticles were characterized by UV-visible, transmission electron microscopy (TEM), scanning electron microcopy (SEM), and X-ray diffraction (XRD) spectroscopic methods. It provides a general methodology for the economic, convenient, mild preparation of citrate-capped noble metal nanoparticles.     

Spontaneous formation of silver nanoparticles on polymeric supports

Silver nanoparticles with a size range of 2-4 nm were prepared on polyethylene glycol-coupled 2-chlorotrityl resins without using any reducing agents. In contrast to the polyol process, silver nanoparticles were simply reduced in the tetrahydrofuran/chloroform system on the resin without using any alcohols, and the resulting silver nanoparticles exhibited a uniform size distribution. The polyethylene glycol spacer on the resin played an important role in obtaining silver nanoparticles, probably acting as a polydentate-chelating agent for the silver ions.     

The formation of supported lipid bilayers on silica nanoparticles revealed by cryoelectron microscopy

The controlled fabrication of biocompatible devices made of lipid bilayers deposited onto flat solid supports presents interest as models of cell membranes as well as for their biotechnological applications. We report here on the formation of supported lipid bilayers on silica nanoparticles (nanoSLBs). The successive steps of the adsorption of lipid vesicles on nanoparticles and the formation of nanoSLBs are revealed in detail by cryotransmission electron microscopy (cryo-EM). The formation of nanoSLBs was achieved for liposomes with positive, neutral, and low net negative charge, while liposomes with a high net negative charge adsorbed to silica nanoparticles but did not rupture. The nanoSLBs were found to follow faithfully the surface contours of the particles, information yet unavailable for SLB formation on planar solid substrates.     

Synthesis of europium-doped yttrium hydroxide and yttrium oxide nanosheets

A new approach has been developed for the preparation of Y(OH)₃:Eu and Y₂O₃:Eu nanosheets using the sol–gel method and hydrothermal reactions. XRD patterns showed that the product was purely hexagonal-phase Y(OH)₃. TEM images revealed that the nanosheets are square shaped (1 × 1 μm²) with a thickness of several tens of nanometers. In addition, it was found that cubic-phase Y₂O₃ nanosheets can be obtained by calcination of Y(OH)₃ at 900 °C for 1 h. More importantly, the thus-prepared Y(OH)₃:Eu and Y₂O₃:Eu nanosheet phosphors were found to exhibit a relatively high photoluminescence (PL) intensity.     

Preparation and characterization of yttrium gallium garnet nanoparticles by citrate sol–gel method at low temperature

The Y₃Ga₅O₁₂ (YGG) nanoparticles with pure phase have been successfully prepared with Y(NO₃)₃ and Ga₂O₃ at lower sintering temperature and shorter holding time. The process of citrate sol–gel method was simple and the cost was very low. The thermal behavior of the YGG precursor was characterized by thermogravimetry/differential thermal analysis (TG/DTA). The crystallization temperature was determined by X-ray powder diffraction (XRPD). The morphology of the particles was characterized by transmission electron microscope (TEM). The results illustrate that the crystallization temperature of YGG nanoparticles was about 700 °C and the powders made by this method dispersed uniformly.     

Spontaneous density grating formation in suspensions of dielectric nanoparticles

Experimental evidence for nonlinear optical behaviour due to the spontaneous formation of wavelength-scale density modulations or gratings in suspensions of dielectric particles is presented. A collection of dielectric particles pumped by a coherent radiation field may simultaneously form a density grating on the scale of the radiation wavelength and a coherently backscattered radiation field. The particle density grating is generated as a result of a periodic ponderomotive potential formed by the interference of the pump and backscattered fields. The experiment used a water suspension of latex microspheres (radius ≈ 56nm) pumped by a green CW laser (532nm, power ≤ 5W). A theoretical model of collective scattering of light from dielectric particles has been extended to include the effects of viscous and Brownian forces on the particles. This model predicts a small degree of particle bunching from which coherent backscattering of the pump occurs. The results of the theoretical model compare favourably with the experimental evidence. The relation between the results presented here and the phenomenon of Collective Rayleigh Scattering (CRS) is discussed.     

The effects of yttrium substitution in Bi-2223 superconductors

Bi_1.7?xY_xPb_0.3Sr₂Ca₂Cu₃O_y (x = 0, 0.05, 0.1 and 0.25) samples were prepared by a conventional solid state reaction method. The influence of Y on structural and superconducting properties has been investigated by XRD measurements, scanning electron microscopy (SEM), dc electrical resistivity, Vickers hardness and magnetic-hysteresis loop measurements. SEM micrographs show that the best surface morphology and largest grain size are observed for undoped samples. The critical transition temperatures of the samples decrease with the increase in the Y content. J_c values of the samples, obtained from Bean’s model, show that J_c decreases with increasing Y content. The mechanical properties of the samples, measured by Vickers hardness (H_v), were found to be load dependent.     

Structural properties of the formation of yttrium germanides thin films on the Si(111) surface

We have performed first principles total energy calculations to investigate the deposit of yttrium digermanide on the Si(111) surface. We have used the periodic density functional theory as implemented in the Quantum-ESPRESSO package. For the adsorption of a monolayer of yttrium digermanide on the Si(111)-(1 × 1) surface, we have found that the most stable geometry corresponds to a configuration with Y atoms occupying the T4 site above a second layer Si atom, and with a Ge bilayer on top of the structure. The atomic structure of the Ge bilayer is similar to that of Si (Ge) in the bulk but rotated 180° with respect to the crystal. For the three dimensional growth of a few layers of yttrium digermanide on Si(111) we have considered a hexagonal structure with (√3 × √3) periodicity, similar to the one found in the growth of few layers of YSi₂ on Si(111): graphite-like Ge planes (with vacancies) intercalated with yttrium planes. As in the case of a single layer of YGe₂, there is a formation of a Ge bilayer on top of the structure. In this case, the Ge_down atoms of the bilayer, which are on top the vacancies, move down towards the vacancy, while Ge atoms in the graphitic layer, which are below the Ge_up atoms of the bilayer, are displaced towards the vacancy.