A Novel Approach to Prepare CaCO3/Polyvinylpyrrolidone (PVP) Composite Nanofibers

A new route to prepare CaCO₃ nanoparticles/polyvinylpyrrolidone (PVP) nanofibers is reported. An aqueous solution of K₂CO₃ was added to a solution of CaCl₂/PVP, resulting in in-situ preparation of CaCO₃ nanoparticles. Then composite nanofibers containing CaCO₃ nanoparticles were successfully prepared by electrospinning. The morphology of the resulting composite nanofibers was characterized by field-emission scanning electron microscopy. In addition, the products were characterized by thermogravimetry analysis and Fourier transform infrared spectra.     

Roles of oleic acid during micropore dispersing preparation of nano-calcium carbonate particles

In the present work, nano-calcium carbonate powder was prepared by micropore dispersion method with assistance of oleic acid as surfactant. CO₂ gas was dispersed into the Ca(OH)₂/H₂O slurry via a glass micropore-plate with the diameter of micropore about 20 μm. To investigate the effect of oleic acid on the size of CaCO₃ particles, different amount of oleic acid was added in Ca(OH)₂/H₂O slurry at 5 °C and 25 °C, respectively. XRD patterns show that cubic calcite is the only crystalline phase in all cases. ZPA data and TEM photo indicate that the average particle size synthesized at 5 °C without oleic acid is of about 40 nm, slightly smaller than that of prepared at 25 °C, and that the dispersity of sample prepared at 5 °C is better than that of 25 °C. When oleic acid is added in both temperatures, the average particle size decreases a little. FT-IR spectra demonstrate that oleic acid interacts with Ca²⁺ and carbon-carbon double bond existed on the surface of particle. Consequently, two opposite roles of oleic acid during the process of preparation of nano-CaCO₃ were proposed, namely preventing nanoparticles from growing during reaction and making nanoparticles reunite to a certain extent after reaction.     

Sol-gel method and luminescence properties of the ZrO<Subscript>2</Subscript>:Eu<Superscript>3+</Superscript> phosphors with different charge compensation

Eu³⁺-doped ZrO₂ phosphors with different charge compensators (Li⁺, Na⁺, K⁺) were prepared by the sol-gel method. The properties of the as-obtained samples are characterized by X-ray diffraction, scanning electron microscope, photoluminescence spectra, and decay curve. The results show that ZrO₂:Eu³⁺ phosphors with different charge compensation are mixed phase of tetragonal and monoclinic phase, and the volume fraction of tetragonal phase of ZrO₂:Eu³⁺/Na⁺ phosphor is bigger than the other phosphors. The phosphors can emit strong red light at 606~616 nm (⁵D₀ → ⁷F₂) excited by ultraviolet light (395 nm). Compared with two charge compensation patterns in the ZrO₂:Eu³⁺, it has been found that ZrO₂:Eu³⁺ phosphors used Na⁺ as charge compensator show greatly enhanced red emission under 395 nm excitation and longer luminescence lifetime.     

Dielectric characteristics and polarization response of lead-free ferroelectric (Bi0.5Na0.5)0.94Ba0.06TiO3-P(VDF-TrFE) 0-3 composites

Bismuth sodium barium titanate/poly(vinylidene fluoride-trifluoroethylene) 70/30 [(Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃-P(VDF-TrFE)] 0-3 composites were prepared by a hot-press method for different volume fractions of (Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ ceramic powder in a P(VDF-TrFE) 70/30 copolymer matrix. The relative permittivity and dielectric loss of the composites increased with increase in the volume fraction of the ceramics, which well follows the Bruggeman model. The polarization responses of the composites were strongly dependent on the ceramic volume fraction. The composites with a higher ceramic volume fraction showed an increase in remanent polarization. At room temperature, a 0.3(Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃-0.7P(VDF-TrFE) composite showed a relative permittivity ε_r=30, remanent polarization and coercive field      

Formation of nickel magnetic nanoparticles and modification of nickel phthalocyanine matrix by sodium doping

Data for the vapor-phase doping (300°C) of nickel phthalocyanine (NiPc) by sodium taken in different concentrations (x), as well as structural analysis data for Na _{x = 0.2}NiPc, Na _{x = 1}NiPc, and Na _{x = 3}NiPc samples, have been reported. The structure of the samples and their atomic configuration versus the doping level have been studied by transmission electron microscopy, Raman scattering, X-ray diffraction, X-ray absorption spectroscopy, and extended X-ray absorption fine structure (EXAFS) spectroscopy. The structural parameters of Ni–N, Ni–C, and Ni–Ni bonds have been determined, and it has been found that, at a low level of doping by sodium, local structural distortions are observed in some molecules of the NiPc matrix near nickel atoms. The fraction of these molecules grows as the doping level rises from x = 0.2 to x = 1.0. It has been shown that doping changes the oscillation mode of light atoms, which indicates a rise in the electron concentration on five- and six-membered rings. At a high level of sodium doping (x = 3.0), nickel nanoparticles with a mean size of 20 nm and molecule decomposition products have been observed in the NiPc matrix. It has been found that the fraction of nickel atoms in the Na _{x = 3}NiPc nanoparticles as estimated from EXAFS data is sufficient for the room-temperature magnetic properties of the samples to persist for a long time.     

Luminescent characteristics of LiCaBo3:M (M=Eu, Sm, Tb, Ce, Dy) phosphor for white LED

LiCaBO₃:M (M=Eu³⁺, Sm³⁺, Tb³⁺, Ce³⁺, Dy³⁺) phosphors were synthesized by a normal solid-state reaction using CaCO₃, H₃BO₃, Li₂CO₃, Na₂CO₃, K₂CO₃, Eu₂O₃, Sm₂O₃, Tb₄O₇, CeO₂ and Dy₂O₃ as starting materials. The emission and excitation spectra were measured by a SHIMADZU RF-540 UV spectrophotometer. And the results show that these phosphors can be excited effectively by near-ultraviolet light-emitting diodes (UVLED), and emit red, green and blue light. Consequently, these phosphors are promising phosphors for white light-emitting diodes (LEDs). Under the condition of doping charge compensation Li⁺, Na⁺ and K⁺, the luminescence intensities of these phosphors were increased.     

Synthesis of rare earth hydroxide nanorods by room temperature reaction of oxide precursors with water

In this study, solid state chemical reaction of anhydrous chloride precursors with Na₂CO₃ has been used to manufacture composite powders of nanocrystalline rare earth oxide grains embedded within a matrix of NaCl. Subsequent washing of these powders with deionised water resulted in removal of the NaCl matrix and hydration of the oxide nanoparticles. In the case of Nd₂O₃ and Sm₂O₃, the hydration process yielded hydroxide nanorods. In contrast, washing of the Gd₂O₃ yielded a powder consisting of irregularly shaped nanoparticles of Gd₂O₃ and GdOOH. Analysis using high resolution transmission electron microscopy revealed that the Nd₂O₃ and Sm₂O₃ nanorods were not single crystals but were composed of crystalline subunits with a common á 0001 ñ \left\langle {0001} \right\rangle growth direction. The results obtained in this study demonstrate that rare earth hydroxide nanorods can be synthesised from oxide precursors without the need for hydrothermal processing at elevated temperature and pressure.     

Magnetic properties of γ-Fe2O3 nanoparticles encapsulated in surface-treated polymer spheres

Mössbauer and magnetic characterization of polymer-dispersed γ-Fe₂O₃ nanoparticles treated under different chemical processes are reported in this work. X-ray powder diffraction analysis provides a mean particle size of D ~ 8.0 nm. Whereas Mössbauer spectroscopy data suggest the presence of only Fe^3?+? ions, magnetization measurements indicate the occurrence of a freezing phenomenon in agreement with the thermal evolution of Mössbauer spectra. A core–shell model was used to determine a magnetically disordered layer (shell) of d ~ 1.0 nm covering a region of collinear magnetic moments (core). The chemical treatments with H₂O₂ and Na₂S₂O₈ modify notoriously the magnetic response of the polymer-dispersed nanoparticles.     

Preparation of CdO nanoparticles by mechanochemical reaction

CdO nanoparticles of 43 nm in crystal size were successfully synthesized by the mechanochemical reaction (CdCl₂ + Na₂CO₃) with NaCl as a diluent and subsequent thermal treatment at 700°C for 2 h. The samples were characterized by differential thermal analysis (DTA), thermogravimetric analysis (TGA), X-ray diffraction (XRD) and transmission electron microscopy (TEM). Effect of calcination temperature on the crystal size of CdO nanoparticles was primarily investigated. The apparent activation energy of CdO nanoparticle formation during thermal treatment was calculated to be 12.2 kJ/mol.     

The system Na2CO3–CaCO3–MgCO3 at 6 GPa and 900–1250°C and its relation to the partial melting of carbonated mantle

In order to constrain the Na₂CO₃–CaCO₃–MgCO₃ T–X diagram at 6?GPa in addition to the binary and pseudo-binary systems we conducted experiments along the Na₂CO₃–Ca_0.5Mg_0.5CO₃ join. At 900–1000°C, melting does not occur and isothermal sections are presented by one-, two- and three-phase regions containing Ca-bearing magnesite, aragonite, Na₂CO₃ (Na₂) and Na₂(Ca_1–0.9Mg_0-0.1)_3-4(CO₃)_4-5 (Na₂Ca_3-4), Na₄(Ca_1–0.6Mg_0–0.4)(CO₃)₃ (Na₄Ca), Na₂(Ca_0-0.08Mg_1–0.92)(CO₃)₂ (Na₂Mg) phases with intermediate compositions. The minimum melting point locates between 1000°C and 1100°C. This point would resemble that of three eutectics: Mgs–Na₂Ca₃–Na₂Mg, Na₂Mg–Na₂Ca₃–Na₄Ca or Na₂Mg–Na₄Ca–Na₂, in the compositional interval of [45Na₂CO₃·55(Ca_0.6Mg_0.4)CO₃]–[60Na₂CO₃·40Ca_0.6Mg_0.4CO₃]. The liquidus projection has seven primary solidification phase regions for Mgs, Dol, Arg, Na₂Ca₃, Na₄Ca, Na₂ and Na₂Mg. The results suggest that extraction of Na and Ca from silicate to carbonate components has to decrease minimum melting temperature of carbonated mantle rocks to 1000–1100°C at 6?GPa and yields Na-rich dolomitic melt with a Na# (Na₂O/(Na₂O?+?CaO?+?MgO))?≥?28?mol%.     

Evaluation of NaFeTiO<Subscript>4</Subscript> as an electrode for energy storage application

We report a polycrystalline NaFeTiO₄ prepared via conventional solid-state reaction route. X-ray diffraction (XRD) results and Rietveld refinement confirmed single-phase NaFeTiO₄ having an orthorhombic unit cell with lattice parameters a = 9.17051 Å, b = 2.96310 Å, and c = 10.73676 Å and Pnma space group (No. 62). Energy dispersive spectrum (EDS) yielded sample stoichiometry that agrees well with its molecular formula. The surface morphology indicated a cylindrical rod-like microstructure comprising well-defined grains having variable dimension, i.e., diameter ~?250 to 350 nm and length ~?1 to 5 μm. Vibrational spectroscopy (FTIR/Raman) results indicated presence of FeO₆ and TiO₆ octahedra in good agreement with crystallographic study. Brunner-Emmet-Teller (BET) surface area measurement yielded a specific surface area as high as ~?4.28 m² g^?1. Electrical impedance spectrum indicated presence of grains separated by well-defined grain boundaries in agreement with microstructural analysis. Electrical conductivity of the material was estimated to be ~?6.05 × 10^?6 S cm^?1. The structural model obtained using XRD and vibrational spectrum results suggest layered tunnel/cage structure of cage dimension ~?4.65 Å, along [010] direction in the xz plane, which is larger than the size of Na⁺ ion (0.98 Å). So, easier Na⁺ migration feasibility exists in NaFeTiO₄ crystal lattice making it a good candidate for electrode applications.     

Laser-induced reactions of NO2 in the visible region

The 488 nm laser-induced reaction of NO₂ with CO has been investigated and the results computer-modeled. Two reaction mechanisms were considered:1) the direct reaction of vibronically excited NO₂ (NO ₂ ^* ) with CO to form CO₂, and 2), the reaction of an intermediate NO₃ radical formed by the reaction of NO ₂ ^* with NO₂ followed by NO₃+CONO₂+CO₂. The modeling results strongly support the former as the dominant mechanism.Federal Junior Fellow (1980–1984)     

Preparation of Aromatic Polycarbonate Nanoparticles using Supercritical Carbon Dioxide

A novel synthetic process for producing aromatic polycarbonate (PC) nanoparticles using supercritical CO₂ was developed. The objective of the present research work was to synthesize high molecular weight PC nanoparticles using transesterification between bisphenol-A (BPA) and diphenyl carbonate (DPC) in supercritical CO₂ which is an excellent plasticizing agent and a good solvent for phenol, a by-product of the reaction. Poly(propylene oxide)–poly(ethylene oxide)–poly(propylene oxide) tri-block copolymer with CO₂-phobic anchor and CO₂-philic tail group was used as a stabilizer for the preparation of stable dispersions of BPA–DPC mixture in a CO₂ continuous phase. As the reaction was proceeding, phenol formed from the reaction was dissolved and diffused into supercritical CO₂ phase. The PC nanoparticles were isolated by simple venting of the supercritical CO₂ from the reactor. Spherical morphology of PC particles was confirmed by scanning electron microscopy. Particle size and morphology of PC particles were modified upon variation of the process conditions. The resulting PC particles with a nano-size of 30–140nm have a high molecular weight (M _w) of 3.1×10⁵ (g/mol).     

Precipitate synthesis of BaMoO4 and BaWO4 nanoparticles at room temperature and their photoluminescence properties

The uniform BaMoO₄ and BaWO₄ nanoparticles (NPs) have been successfully synthesized by solution route – the direct precipitation of Ba(NO₃)₂ and Na₂MO₄ (M = Mo and W) in ethylene glycol under 24 h stirring. The XRD patterns and SEM images proved that the products were tetragonal structured BaMoO₄ and BaWO₄ with uniform round nanoparticles. Shape, average particle size and particle-size distribution of products were analyzed by TEM – showing the round nanoparticles with the average size of 31.52 ± 4.65 nm for BaMoO₄, and 59.77 ± 9.61 nm for BaWO₄. The room temperature photoluminescence (PL) indicated that the products have strong blue emission centered at 441 nm – excited with 280 nm wavelength for BaMoO₄ NPs, and strong violet emission centered 378 nm – excited with 344 nm wavelength for BaWO₄ NPs. These PL behaviors attributed the existence of intrinsic transitions in the [MO₄]^2-$[{\text{MO}}_4{]}^{2-}$ (M = Mo and W) tetrahedrons of their crystal lattices.     

Synthesis of nano-size BaMgAl10O17:Eu blue phosphor by a rapid exothermic reaction

Ultrafine particles of BaMgAl₁₀O₁₇:Eu²⁺ (BAM) phosphor were synthesized by a solid-state combustion reaction in a powder bed of 0.9BaCO₃+MgO+5Al₂O₃+0.05Eu₂O₃+k(KClO₃+1.5C) composition. A large exothermic reaction of the mixture (KClO₃+1.5C) leads to a self-sustaining combustion mode. Under optimized combustion conditions, the product consisted of BAM powder and KCl was obtained. BAM ultrafine particles resulting from the combustion process were easily obtained by simply washing the salt by-product with water. Combustion-processed BAM phosphor shows a homogeneous grain size of 100-500 nm, good dispersity, regular morphology, and improved luminescence properties.     

In situ preparation of hydrophobic CaCO3 in the presence of sodium oleate

Hydrophobic CaCO₃ particles were directly prepared via carbonation of Ca(OH)₂ slurry in the presence of sodium oleate at room temperature. Sodium oleate was used to modify the surface property of CaCO₃ particles. The measurement of relative contact angle and active ratio indicated that CaCO₃ samples were hydrophobic. DTG, FT-IR and TEM analysis of the obtained product indicated that the hydrophobic property was attributed to the deposition of calcium oleate, produced in the reaction mixture, onto the surface of calcium carbonate particles. They were covered on the CaCO₃ crystals surface and modified their surface property; at the same time they own CC bonds and could be polymerized or copolymerized later to give a polymeric monolayer.     

Rapid synthesis and size control of CuInS2 semi-conductor nanoparticles using microwave irradiation

The properties of CuInS₂ semi-conductor nanoparticles make them attractive materials for use in next-generation photovoltaics. We have prepared CuInS₂ nanoparticles from single source precursors via microwave irradiation. Microwave irradiation methods have allowed us to increase the efficiency of preparation of these materials by providing uniform heating and rapid reaction times. The synergistic effect of varying thiol capping ligand concentrations as well as reaction temperatures and times resulted in fine control of nanoparticle growth in the 3–5 nm size range. Investigation of the photophysical properties of the colloidal nanoparticles were performed using electronic absorption and luminescence emission spectroscopy. Qualitative nanoparticles sizes were determined from the photoluminescence (PLE) data and compared to HRTEM images.

Synthesis of indium oxide nanoparticles by solid state chemical reaction

A three stage process consisting of mechanical milling, heat treatment, and washing has been investigated as a means of manufacturing nanoparticulate powders of In₂O₃. In the first stage of processing, mechanical milling was used to prepare a nanocrystalline mixture of In₂(SO₄)₃, Na₂CO₃, and NaCl. Subsequent heat treatment of the milled reactant resulted in the formation of nanocrystalline In₂O₃ particles embedded within a matrix of Na₂SO₄ and NaCl. In the final stage of processing, the In₂O₃ powder was recovered by washing with deionised water. The duration of milling was found to determine the degree of hard agglomeration in the final washed powder. It was also found that the average particle size of the powder could be controlled between 8 and 18 nm by simply varying the temperature of the post-milling heat treatment over the range of 400 to 550°C. These results demonstrate that solid state chemical reaction can be used as a technically simple method for manufacturing nanoparticulate In₂O₃ powders with a controlled particle size and low levels of hard agglomeration.     

Characteristics of Fe2O3 Nanoparticles from Doped Low-pressure H2/O2/Ar Flames

A burner stabilized premixed low-pressure flame has been used to generate iron-oxide (Fe₂O₃) nanoparticles with sizes in the range 7–20nm. The H₂/O₂/Ar flames were doped with different amounts of iron-pentacarbonyl (Fe(CO)₅) with concentrations in the range 524–2096ppm. The influence of precursor concentration on composition, structure, morphology, and size have been studied utilizing transmission electron microscopy (TEM), X-ray powder diffraction (XRD), measurements of the specific surface area (BET), and infrared spectroscopy (FT-IR). The product particles consist of both, the - and the -phase of Fe₂O₃. Average particle sizes were measured in the range 7.4–16nm depending on precursor concentration and flame conditions.     

Enhanced luminescence of Ca3B2O6:Dy phosphors by Na-codoping for LED applications

The Ca_2.95−yDy_0.05B₂O₆:yNa⁺ (0≤y≤0.20) phosphors were synthesized at 1100 °C in air by the solid-state reaction route. The as-synthesized phosphors were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), photoluminescence excitation (PLE), photoluminescence (PL) spectra and thermoluminescence (TL) spectra. The PLE spectra show the excitation peaks from 300 to 400 nm due to the 4f-4f transitions of Dy³⁺. This mercury-free excitation is useful for solid-state lighting and light-emitting diodes (LEDs). The emission of Dy³⁺ ions on 350 nm excitation was observed at 480 nm (blue) due to the ⁴F_9/2→⁶H_15/2 transitions, 575 nm (yellow) due to ⁴F_9/2→⁶H_13/2 transitions and 660 nm (red) due to weak ⁴F_9/2→⁶H_11/2 emissions. The PL results from the investigated Ca_2.95−yDy_0.05B₂O₆:yNa⁺ phosphors show that Dy³⁺ emissions increase with the increase of the Na⁺ codoping ions. The integral intensity of yellow to blue (Y/B) can be tuned by controlling Na⁺ content. By the simulation of white light, the optimal CIE value (0.328, 0.334) can be achieved when the content of Na⁺-codoping ions is y=0.2. The results imply that the Ca_2.95−yDy_0.05B₂O₆:yNa⁺ phosphors could be potentially used as white LEDs.