Preparation,microstructure and electrochemical performance of nanoparticles LiMn2O3.9Br0.1

LiMn₂O_3.9Br_0.1 nanoparticles were prepared by a room-temperature solid-state coordination method. The structure and morphology of the as-prepared materials were analyzed by X-ray diffractometry and transmission electron microscopy. The results show that the LiMn₂O_3.9Br_0.1 is well-crystallized and consists of monodispersed nanoparticles 80–100 nm in size. Results of electrochemical testing show that the samples prepared at different temperatures have similar electrochemical performance. The initial discharge capacities of LiMn₂O_3.9Br_0.1 prepared at 800 °C and 700 °C are 121 mAh g^? 1 and 118.9 mAh g^? 1, respectively, higher than for LiMn₂O₄ prepared using the same method.     

Three-dimensionally ordered macroporous Ti1−xTaxO2+x/2 (x = 0.025, 0.05, and 0.075) nanoparticles: Preparation and enhanced photocatalytic activity

Anatase phase, three-dimensionally ordered macroporous (3 DOM) Ti_1−xTa_xO_{2 + x / 2} (x = 0.025, 0.05, and 0.075) nanoparticles with macropore diameter 290 to 310 nm, wall thickness 50 to 80 nm, and particle size 10 to 12 nm were prepared by combination of the sol–gel chemistry and polystyrene (PS) templating procedure. The products exhibited relatively narrower band gaps and larger BET surface areas than those of the starting solitary 3 DOM metal oxides, and their photocatalytic activities for the degradation of an aqueous 4-nitrophenol remarkably enhanced compared with 3 DOM anatase TiO₂, Ta₂O₅, and Degussa P-25.     

Low temperature synthesis,crystal structure and thermal stability studies of nanocrystalline VN particles

The simultaneous thermal decomposition and nitridation of [VO(NH₂O)₂Gly]·H₂O complex in NH₃ atmosphere at 723–973 K gives the nanocrystalline vanadium nitride (VN) having crystallite size of 8–32 nm. It shows cubic NaCl structure with lattice parameter of a = 4.137 nm. XRD pattern Rietveld analysis program for crystal structure of VN shows the space group-Fm3m. The particle sizes measured by BET and SEM techniques are in the range of 26–100 nm. The particles are spherical and distributed homogeneously and found larger than XRD crystallite size because of agglomeration of crystallites. The fundamental IR absorption of VN material is found at 995 cm⁻¹ which gives the force constant of 634.3 Nm⁻¹. The electrical resistivity and magnetic studies show the superconducting to normal transition (T_c) at 9.2 K. Thermal decomposition of VN is carried out in O₂ atmosphere which goes through the formation of an oxynitride (V–N_p–O_q) intermediate phase up to 913 K. Finally, nanocrystalline V₂O₅ is formed at 973 K. The V₂O₅ has orthorhombic structure with lattice parameters of a = 11.537, b = 3.568 and c = 4.380 Å and the XRD crystallite size of 10 nm.     

Synthesis of nanocrystalline GaN from Ga2O3 nanoparticles derived from salt-assisted spray pyrolysis

Gallium nitride (GaN) nanoparticles were successfully produced from nano-sized gallium oxide (Ga₂O₃) particles under a flow of ammonia gas. The gallium oxide nanoparticles were prepared by salt-assisted spray pyrolysis (SASP). Highly crystalline Ga₂O₃ nanoparticles with an average diameter of approximately 10 nm were obtained at various temperatures when a flux salt (LiCl, 5 mol/l) was added to the precursor solution. The effects of the crystallinity of the Ga₂O₃ particles and nitridation time on transformation to GaN were characterized using X-ray diffraction and scanning/transmission electron microscopy. Highly crystalline GaN nanoparticles with a mean size of 23.4 nm and a geometric standard deviation of 1.68 nm were obtained when Ga₂O₃ nanoparticles with relatively low crystallinity were used as the starting material. The resulting GaN nanoparticles showed a photoluminescence peak at 364 nm under UV excitation at 254 nm.     

Compositional variation of photoluminescence from Mn doped MgAl2O4 spinel

Spinel (MgAl₂O₄) crystals doped with 1.0% Mn have been grown by floating zone (FZ) technique with various Mg compositions, x = MgO/Al₂O₃, from 0.2 to 1.0. Compositional variations of photoluminescence are evaluated for a fluorescence thermometer application using crystals grown. Strong photoluminescence (PL) peak is observed at λ from 512 to 520 nm from the crystals grown from compositions, x, from 0.3 to 1.0. Peak wavelength of PL increases linearly from 512 to 520 nm with x. Weak PL peaking at λ = 750 nm is also observed from the specimens. Compositional variations of PL are considered to be due to the variation of crystal field surrounding the Mn²⁺ ions. The variation of crystal field strength agrees with the compositional variation of lattice constant.     

Thermal decomposition synthesis of 3D urchin-like α-Fe2O3 superstructures

Urchin-like α-Fe₂O₃ superstructures have been deposited on Si substrate using thermal decomposition FeCl₃ solution at 200–600 °C in the oven. The morphologies and structures of the synthesized urchin-like superstructures have been characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The results show that urchin-like α-Fe₂O₃ superstructures were a polycrystal with the rhombohedral structure and typical diameters of 16–20 nm and lengths up to 1.0 μm. The as-prepared α-Fe₂O₃ superstructures have a high Brunauer–Emmett–Teller (BET) surface area of about 60.24 m²/g. The photoluminescence spectrum of the urchin-like α-Fe₂O₃ superstructures consists of one weak emission peak at 548 nm (2.26 eV). A possible new mechanism for the formation of the urchin-like superstructures was also preliminarily discussed.     

Investigation on the luminescence of RE3+ (RE = Ce,Tb, Eu and Tm) in KMGd(PO4)2 (M = Ca,Sr) phosphates

The VUV excited luminescent properties of Ce³⁺, Tb³⁺, Eu³⁺ and Tm³⁺ in the matrices of KMGd(PO₄)₂ (M = Ca, Sr) were investigated. The bands at about 165 nm and 155 nm in the VUV excitation spectra are attributed to host lattice absorptions of the two matrices. For Ce³⁺-doped samples, the Ce³⁺ 5d levels can be identified. As for Tb³⁺-doped samples, typical 4f–5d absorption bands in the region of 175–250 nm were observed. For Eu³⁺ and Tm³⁺-doped samples, the O²⁻–Eu³⁺ and O²–Tm³⁺ CTBs are observed to be at about 229 nm and 177 nm, respectively. From the standpoints of color purity and luminescent efficiency, KCaGd(PO₄)₂:Tb³⁺ is an attractive candidate of green light PDP phosphor.     

A simple method to prepare indium oxide nanoparticles: Structural,microstructural and magnetic properties

Indium oxide nanoparticles of ～12 nm were synthesized by a simple chemical route using indium(III) nitrate. Nanoparticles are formed after calcining the dried precursor in air at 400 °C for 10 h. TEM analysis showed that the morphology and size of the In₂O₃ samples were affected by ultrasonication. FTIR and Raman studies reveal that the nanoparticles are single-phase cubic structure of In₂O₃. NEXAFS study was used to quantify the Indium and oxygen valence state. Magnetic behavior of indium oxide nanoparticles was found to be diamagnetic. UV spectra show a weak band at ～308 nm corresponds to optical band gap energy of 4.03 eV.     

Synthesis and characterization of ultrafine Ln2Ti2O7 (Ln = Sm,Gd, Dy,Er) pyrochlore oxides by stearic acid method

Stearic acid method (SAM) was developed to synthesize series of pyrochlore Ln₂Ti₂O₇ (Ln = Sm, Gd, Dy, Er) nanocrystals. The synthesis process was monitored by X-ray diffraction, Thermal–gravimetric–differential thermal analysis and Fourier Transform InfraRed methods. Comparing with traditional solid-state reaction (SSR), Ln₂Ti₂O₇ can be synthesized at relatively low temperature (700–800 °C) with shortened reaction time (2–4 h). The average particle size of Ln₂Ti₂O₇ was greatly reduced (ca. 40 nm) and the BET surface area was increased (ca. 12 m²/g) by using SAM. From the X-ray diffraction patterns, we found that Ln has an effect on the crystal structure of Ln₂Ti₂O₇, every lattice peak shifted to larger angle slightly with the increasing atomic number of Ln. Also, the lattice constant of Ln₂Ti₂O₇ was calculated by Jade.5 and found it decreased along with the decrease of ionic radius of Ln³⁺. The morphology of obtained Ln₂Ti₂O₇ was determined by transmission electron microscopy technique. Results showed that the obtained Ln₂Ti₂O₇ were all square-like and the interplanar distance of Ln₂Ti₂O₇ (Ln = Sm, Gd, Dy, Er) according to (111) plane was 0.65, 0.64, 0.63, and 0.62 nm respectively, which was measured from High Resolution Transmission Electron Microscopy images. Possible reason for this phenomenon was presented.     

Synthesis of magnesium borate (Mg2B2O5) nanowires,growth mechanism and their lubricating properties

Large quantities of single crystalline magnesium borate nanowires of the form Mg₂B₂O₅ with typical diameter about 120–180 nm and length about 0.2 mm have been successfully synthesized by a new and simple method of heating the mixed tablet of Mg(BO₂)₂ and graphite directly in vacuum at 1200 °C for 1 h. The products have been characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectrometry and selected area electron diffraction. The process of the nucleation and the growth of nanowires have been analyzed by VS mechanism. The results of the lubricating properties show that the friction coefficient of the oil is significantly decreased by the addition of Mg₂B₂O₅ nanowires. Our results indicate that the new method we use is effective in synthesis of Mg₂B₂O₅ nanowires and the nanowires can be used as additive to antiwear nanodevices.     

Synthesis of crystal MFe2O4 (M = Mg,Cu, Ni) microspheres

A low-temperature solvothermal synthetic method was developed for the large-scale synthesis of uniform-sized ferrite MFe₂O₄ (M = Mg, Cu, Ni) microspheres. The size of the as-prepared ferrite MFe₂O₄ microspheres could be controlled to be diameters 300–800 nm in diameter by adjusting some growth parameters, such as reaction time and concentration. The structures of the as-prepared ferrite MFe₂O₄ microspheres were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDAX). The magnetic properties of the ferrite MFe₂O₄ microspheres were also investigated.     

Mechanochemical carboaluminothermic reduction of rutile to produce TiC–Al2O3 nanocomposite

This investigation aims to produce TiC–Al₂O₃ nanocomposite by reducing rutile with aluminum and graphite powder via a mechanochemical process. The effect of milling time on this process was investigated. The characterization of phase formation was carried out by XRD and SEM. Results showed that after a 10 h milling, the combustion reaction between Al, TiO₂ and C was started and promoted by a self-propagation high temperature synthesis. Extending the milling time to 20 h, the reaction was completed. The XRD study illustrated after a 20 h milling, the width of TiC and Al₂O₃ peaks increased while the crystallite sizes of these phases decreased to less than 28 nm. After annealing at 800 °C for 1 h in a tube furnace, TiC and Al₂O₃ crystallite sizes remained constant. However, raising the annealing temperature to 1200 °C caused TiC and Al₂O₃ crystallite size to increase to 49 nm and 63 nm, respectively. No new phase was detected after the heat treatment of the synthesised TiC–Al₂O₃ nanocomposite.     

Enhancement of photoluminescence properties of CaAl2Si2O8:Eu2+ by SiO2 addition

SiO₂ added phosphors, CaAl₂Si₂O₈:Eu²⁺ + xSiO₂ (x = 0, 1, 2, 3, 4, 5, 6 and 13 mol) were synthesized by a novel liquid phase precursor (LPP) method. The photoluminescence properties of phosphor added by 5 mol of SiO₂ showed 110% enhancement in the emission intensity compared to the CaAl₂Si₂O₈:Eu²⁺ phosphor. A broad emission and excitation wavelength was observed approximately from 400 nm to 600 nm centered at 430 nm and from 280 nm to 400 nm centered at 365 nm, respectively. Photoluminescence intensity of the phosphors increased continuously by SiO₂ addition up to x = 5 mol and then it decreased with further addition of SiO₂. The observed photoluminescence properties of the phosphors were discussed related to their crystalline structure and morphology.     

Synthesis of nanocrystalline Ni0.5Zn0.5Fe2O4 ferrite and study of its magnetic behavior at different temperatures

Ni_0.5Zn_0.5Fe₂O₄ ferrite nanocrystals with average diameter in the range of 1–2 nm have been synthesized by reverse microemulsion. X-ray diffraction (XRD), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM) are used to characterize the structural, morphological and magnetic properties. X-ray analysis showed that the nanocrystals possess cubic spinel structure. The absence of hysteresis, negligible remanence and coercivity at 300 K indicate the superparamagnetic character and single domain in the nanocrystalline Ni_0.5Zn_0.5Fe₂O₄ ferrite materials. The nanocrystalline Ni_0.5Zn_0.5Fe₂O₄ ferrite were annealed at 600 °C. As a result of heat treatment the average particle size increases from 2 nm to 5 nm and the corresponding magnetization values have increased to 21.69 emu/g at 300 K. However, at low temperature of 100 K, the annealed samples show hysteresis loop which is the characteristic of a superparamagnetic to ferromagnetic transition. In addition, a comparative study of the magnetic properties of Ni_0.5Zn_0.5Fe₂O₄ ferrite nanocrystals obtained from reverse microemulsion has been carried out with those obtained from the general chemical co-precipitation route.     

Preparation and luminescent properties of Cr3+:Al2O3 nano-powders by low-temperature combustion synthesis

Cr³⁺:Al₂O₃ nano-powders were prepared through low-temperature combustion synthesis (LCS) method by using glucose as a dispersion agent for the first time. The Cr³⁺:Al₂O₃ nano-powders samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and luminescence spectrometer. XRD results showed that pure α-Al₂O₃ phase was obtained for the sample fired at 1100 °C for 0.5 h. TEM results indicated that nano-powders were well dispersed. Luminescence spectrum analysis results indicated that the excitation spectrum of Cr³⁺:Al₂O₃ nano-powders consisted of two bands peaking at 462 nm and 579 nm, respectively, and the emission spectrum consisted of two bands peaking at 692 nm and 668 nm, respectively.     

Synthesis and functionalization of SiO2 coated Fe3O4 nanoparticles with amine groups based on self-assembly

The purpose of this research was to synthesize amino modified Fe₃O₄/SiO₂ nanoshells for biomedical applications. Magnetic iron-oxide nanoparticles (NPs) were prepared via co-precipitation. The NPs were then modified with a thin layer of amorphous silica. The particle surface was then terminated with amine groups. The results showed that smaller particles can be synthesized by decreasing the NaOH concentration, which in our case this corresponded to 35 nm using 0.9 M of NaOH at 750 rpm with a specific surface area of 41 m² g^? 1 for uncoated Fe₃O₄ NPs and it increased to about 208 m² g^?1 for 3-aminopropyltriethoxysilane (APTS) coated Fe₃O₄/SiO₂ NPs. The total thickness and the structure of core-shell was measured and studied by transmission electron microscopy (TEM). For uncoated Fe₃O₄ NPs, the results showed an octahedral geometry with saturation magnetization range of (80–100) emu g^?1 and coercivity of (80–120) Oe for particles between (35–96) nm, respectively. The Fe₃O₄/SiO₂ NPs with 50 nm as particle size, demonstrated a magnetization value of 30 emu g^?1. The stable magnetic fluid contained well-dispersed Fe₃O₄/SiO₂/APTS nanoshells which indicated monodispersity and fast magnetic response.     

Preparation and magnetic property of Fe2O3 parallelepiped nanocrystals

Well-dispersed α-Fe₂O₃ parallelepiped nanocrystals have been successfully prepared via a hydrothermal synthetic route. The shapes and structures of the products were characterized by using powder X-ray diffraction and scanning electron microscopy. The results showed that the α-Fe₂O₃ samples have a parallelepiped shape with an average parallel side of 80–90 nm and thickness of 60–70 nm. The parallelepiped nanocrystals exhibited a ferromagnetic behavior with the coercive force, saturation magnetization, and remanent magnetization of 920 Oe, 0.44 emu/g, and 0.17 emu/g, respectively. The crystal growth process was discussed on the basis of time-dependent experimental results.     

Fabrication,superhydrophobicity, and microwave absorbing properties of the magnetic γ-Fe2O3/bamboo composites

Magnetic γ-Fe₂O₃ nanoparticles were successfully deposited on the surface of the bamboo via a coprecipitation process at room temperature. Spherical-like magnetic γ-Fe₂O₃ nanoparticles with a diameter of about 17 nm displayed well superparamagnetic behavior and were chemically bonded to the bamboo surface through the combination of hydrogen groups. With further modification by 1H,1H,2H,2H-perfluorodecyltri ethoxysilane (FAS-17), magnetic γ-Fe₂O₃/bamboo composites (MBCs) expressed superhydrophobic performances to not only water but also common liquids like coffee, milk, ink, tea, and coke. When immersed into the corrosive solutions including strong acid (pH = 1), heavy alkaline (pH = 14), and salt with high concentration (5 M) for 24 h, superhydrophobic magnetic γ-Fe₂O₃/bamboo composites (SMBC) still remained magnetism as well as superhydrophobicity. Also, under harsh conditions like boiled at 100 °C for 4 h, frozen at − 40 °C for 24 h, SMBCs were kept a robust magnetism and superhydrophobicity. Additionally, SMBC was a typical ferromagnet and exhibited some microwave absorbabilities.     

Comparative study of the luminescence of Al2O3:Ti and Al2O3 crystals under VUV synchrotron radiation excitation

The comparative study of the luminescent properties of Al₂O₃:Ti crystal in comparison with those for undoped Al₂O₃ crystal counterpart is performed under synchrotron radiation excitation with an energy of 3.7–25 eV. Apart from the main emission band peaked at 725 nm related to the ²E → ²T₂ radiative transitions of Ti³⁺ ions, the luminescence of excitons localized around Ti ions in the band peaked at 290 nm and the luminescence of F⁺–Ti and F–Ti centers in the bands peaked at 325 and 434 nm are also found in the emission spectra of Al₂O₃:Ti crystal. We show also that the luminescence of Ti³⁺ ions in Al₂O₃:Ti crystal can be effectively excited by the luminescence of excitons localized around Ti dopant as well as by the luminescence of F–Ti centers.     

A promising birefringent crystal Ba2Na3(B3O6)2F

Bulk crystals of Ba₂Na₃(B₃O₆)₂F (BNBF) have been successfully grown by top-seeded solution growth (TSSG) technique. Its transmittance spectra show a wide transparency range from 186 nm to 3000 nm. The refractive indices in 13 wavelengths were measured with high accuracy and the Sellmeier equations were obtained, which demonstrated that the title crystal displayed a birefringence (Δn = 0.1030 at 588 nm) comparable to that of the commercial birefringent crystal α-BBO (the high temperature form of BaB₂O₄). A prototype Glan-Taylor polarizer made of BNBF prisms was fabricated, which showed high transparency and large optical extinction ratio similar to the commercial polarizer made of α-BBO. In addition, BNBF crystal is less moisture sensitive than that of α-BBO, thus BNBF can be a potential new birefringent crystal.