Preparation of niobium based oxynitride nanosheets by exfoliation of Ruddlesden-Popper phase precursor

A new oxynitride Ruddlesden-Popper phase K_1.6Ca₂Nb₃O_9.4N_0.6.1.1H₂O was synthesized by the topochemical ammonolysis reaction at 700 °C from the oxide Dion-Jacobson phase KCa₂Nb₃O₁₀ in the presence of K₂CO₃. The oxynitride showed good stability with a little loss of nitrogen, even after a few months of exposure to air. Its crystal structure was solved by Rietveld refinement of X-ray powder diffraction data in space group P4/mmm and considering a two-phase mixture, due to the difference in the degree of hydration, with a = 3.894(2) Å and c = 17.90(8) Å for the most hydrated phase and a = 3.927(6) Å and c = 17.09(2) Å for the less one. Optical band gaps were measured by diffuse reflectance in the UV-Visible range indicating a red shift of Eg to the visible region. The oxynitride layered perovskite was then protonated and exfoliated into nanosheets. TEM images and SAED patterns of the nanosheets proved that exfoliation was successful, showing lattice parameters quite compatible with the Rietveld refinement.     

溶剂热法制备银纳米晶

以聚乙烯吡咯烷酮(PVP)作为表面活性剂,利用乙二醇溶剂热法成功制备了银纳米颗粒;利用场发射扫描电子显微镜(FE-SEM)、透射电子显微镜(TEM)、X射线衍射(XRD)分析了样品的形貌和晶体结构,并考察了溶剂组成等因素对银纳米颗粒形貌的影响.研究结果表明所得银纳米晶粒径均一,直径约为90nm;增大PVP的加入量会降低产物的粒径,溶剂中水的引入会影响银纳米晶的形貌.     

Preparation and characterization of mixed alkyl amido complexes of gallium

A series of primary amido gallium alkyl complexes that includes a base free dimer, [^tBu₂Ga(μ-N(H)^tBu)]₂ (1), Lewis base stabilized monomeric complexes, ⁿBu₂Ga(N(H)^tBu)(THF) (2) and ⁿBu₂Ga[NH(2,6-Me₂C₆H₃)]py (3) and an anionic complex, ⁿBu₂Ga[NH(2,6-Me₂C₆H₃)]₂[Li(Et₂O)] (4) is reported. Complex 1 crystallizes in the triclinic space group P-1 (a = 10.265(5) Å, B = 15.752(6) Å, C = 8.932(4) Å, = 90.32(3)°, β = 105.61(3)°, γ = 88.24(4)°) with two molecules, each residing on an inversion center, in the asymmetric unit. Structural analysis revealed a planar Ga₂N₂ core with both the bridging N and the Ga centers in distorted tetrahedral environments (Ga---C distances 2.052(3)-2.065(3) Å and Ga---N distances 2.060(3)-2.069(3) Å). The use of excess amido ligand allowed the isolation and crystallization of 4. Complex 4 crystallized in the monoclinic space group P21/n (a = 8.666(2) Å, B = 22.305(3) Å, C = 15.570(3) Å, β = 103.47(2)) with Z = 4. The pseudotetrahedral gallium center has a coordination sphere composed of two amido ligands (Ga---N1 = 2.011(8) Å, Ga---N2 = 2.006(7) Å), and two ⁿBu ligands (Ga---C17 = 2.002(9) Å Ga---C21 = 1.985(12) Å). A bridging interaction of the lithium cation with the lone pair of electrons on each of amido nitrogen atoms generates a molecular core which is made up of a planar Ga---N1---Li---N2 distorted square (N1---Gal---N2 94.4°, Gal---N2---Lil 86.2°, N1---Li1---N2 92.2°, Gal---N1---Li1 87.1°).     

溶剂热法制备八面体纳米结构四氧化三铁

利用乙二醇溶剂热法成功制备了八面体结构四氧化三铁,利用场发射扫描电子显微镜、透射电子显微镜、选区电子衍射仪、X射线衍射仪及超导量子干涉仪分析了合成产物的形貌、晶体结构及磁学性能,并探讨了多种实验条件对纳米结构形成的影响.结果表明所得八面体四氧化三铁纳米晶粒径均一,棱边尺寸约为120nm,室温下显示铁磁性质.     

Preparation and evaluation of ammonia decomposition catalysts by high-throughput technique

The high-throughput technique has been successfully employed to investigate systematically NH₃ decomposition catalysts for COx-free hydrogen production. Supported γ-Mo₂N catalysts not only could be prepared and evaluated by the high-throughput experiment, but are also active for NH₃ decomposition luke supported Ni and Co catalysts. Additionally, the preparation process and support play important roles on the catalytic performance of supported γ-Mo₂N catalysts.     

Preparation via the polymer route and photoluminescence properties of CeSi3N5

CeSi₃N₅ has been prepared via the polymer route, a one-pot and liquid-phase synthesis, based on a reaction between SiCl₄ and liquid NH₃ in which Ce[N(Si(CH₃)₃)₂]₃ was suspended. The sample was characterized by powder X-ray diffraction analysis, diffuse reflection and photoluminescence spectroscopies. CeSi₃N₅ exhibits a strong absorption peaking at 365 nm. Furthermore, it has a broad emission band at 468 nm due to 4f⁰5d¹ → 4f¹ transition of Ce³⁺. Obviously, CeSi₃N₅ appears to be a good candidate for use as a blue phosphor, which can be pumped by near-UV-LEDs.     

Synthesis of LiNbO3 via a hydrothermal route and characterization

Lithium niobate (LiNbO3) crystal, used in many optical fields, has been of great interest for fundamental science and applications in optics for many years due to its excellent ferroelectric properties such as piezoelectricity, pyroelectrical, electro-optical, photorefractive and nonlinear-optical properties. Several methods for synthesizing lithium niobate crystal have been reported, for instance Czochralski growth, top seeded solution growth (TSSG), liquid phase epitaxy,laser deposition, chemical vapor deposition and sol-gel and so on. Although these methods have many advantages, they also have some disadvantages. For example, Lithium ethoxide and Niobium ethoxide are the most common reactants in sol-gel method. But, it is known to all that they are unstable in air and water. So, we have to take the course under the protection of N2 gas. This drawback complicates the process considerably.In this paper, LiNbO3 crystal was successfully prepared via a simple and convenient hydrothermal route using LiOH and Nb2O5 (molar rate=2:1) as the starting reactants. The whole reaction process was carried in an autoclave made by us, showed in fig. 1. The typical procedure was described as follow: first, distilled water was poured into the autoclave until 50% to 80% of its volume was filled. Then the reagents were added in succession. After that, the autoclave was sealed and maintained at 260℃ for 72 hours and then cooled to room temperature naturally. The obtained sample was washed with distilled water and absolute alcohol for several times to remove the by-products and other impurities. After drying, the obtained sample was characterized by XRD and IR.XRD patterns of the as-prepared sample showed that the sample was well crystallized and of high purity. All the major reflection peaks were appeared and accorded with the reported data in the literature. In addition, no other impurities, such as Nb2O5 and Li3NbO4, were detected in the sample.The as-prepared sample was dispersed into paraffine and characterized using IR spectra. The absorption bands observed at contamination on the surface of the as-prepared sample. This result was different from the pre-works in which the absorption bands were observed between from 3400cm-1 to 3500cm-1. This may be attributable to the size of crystal in the current work was smaller than the in pre-works.It has been reported that there are four absorptions for lithium niobate crystal over the wavenumber range 400-800cm-1 at 783cm-1, 630cm-1, 595cm-1 and 500cm-1, respectively. These were the characteristic lithium niobate IR finger printing absorptions. In H. C. Zen-g's work, the four characteristics absorptions were observed at 800cm-1, 675cm-1, 595cm-1 and 440cm-1, respectively. In the current work, there were three characteristic absorptions were detected at 693.4cm-1, 646.2cm-1 and 437.0cm-1, respectively. This result was accorded with the pre-works.     

General synthesis of metal sulfides nanocrystallines via a simple polyol route

In this report, a simple and easy polyol route for synthesizing many binary metal sulfides nanocrystallines is demonstrated. Powder X-ray electron diffraction and energy-dispersive X-ray spectrum are applied to investigate the crystallinity and composition of the nanoscale materials. The resulting particle size and morphology are examined by transmission electron microscopy, and the possible mechanism is also briefly discussed.     

Spectrophotometric and colorimetric determination of gallium (III) with p-aminohippuric acid-functionalized citrate capped gold nanoparticles

A new technique for sensing Ga(III) concentration based on polyvinyl alcohol-citrate capped gold nanoparticle– p- aminohippuric acid hybrid (or three-layer core-shell configurations) has been demonstrated. The p- aminohippuric acid capped citrate-gold nanoparticles were comfortably agglomerated in the presence of Ga(III), and the color of the reaction quickly turned from red to violet or blue. Under the detection conditions, a good linear relationship was ideally obtained between the ratio of the absorbance intensity at 620 nm to that at 520 nm (A₆₂₀/A₅₂₀). The linear response range, the detection, and quantification limit was 34.9–418.3 μg/L and 7.6 μg/L, and 25 μg/L, respectively. To reflect the accuracy, the developed sensing approach was evaluated against certified reference materials (TMDA 51.3 fortified water and TMDA 28.3 fortified water). This colorimetric strategy was displayed excellent selectivity for Ga(III) over other examined ions. Additionally, the colorimetric method was properly used to detect the concentrations of Ga in tap water and certified reference material samples with recoveries ranging from 95.4 to 102.0%, displaying that the colorimetric procedure could be safely used for a realistic application.     

Total synthesis of leustroducsin B via a convergent route

Total synthesis of leustroducsin B was achieved via a convergent route, which includes Julia coupling reaction of segment A with segment B followed by Stille coupling reaction of segment C.     

Density functional theory predictions for blue luminescence and nonlinear optical properties of carbon-doped gallium nitride

The TD-B3LYP method and the plane-wave formalism of DFT method were applied to predict the blue luminescence and nonlinear optical effect of C-doped GaN, respectively. The introduction of carbon dopant will generate different acceptor or donor levels, which are mainly composed by p electronic state, within the energy gap of GaN. Exploring the calculated luminescence spectra based on the optimized excited-state structure, C_N:GaN exhibits high luminescence intensity and has nice monochromatic property. In addition, the corresponding second-order nonlinear optical coefficients are considerable, χ⁽²⁾_xzx=−15.07 pm/V and χ⁽²⁾_zzz=26.91 pm/V, which are about 28 times and 50 times of the second-order optical coefficient of KDP crystal.     

Phase evolution of lead titanate from its amorphous precursor synthesized by the OPM wet-chemical route

Lead titanate was synthesized by the OPM wet-chemical route by the dissolution of Ti metal in H₂O₂ followed by the addition of Pb²⁺ at high pH, resulting in a reactive and amorphous precipitate with (Pb:Ti=1:1) mole ratio, which was heat treated between 400°C and 700°C. The amorphous precipitate was characterized by DSC, and all of the powders were characterized by X-ray diffraction, Raman and XAS (EXAFS and XANES) spectroscopy at the Ti K edge. A metastable, stoichiometric and cubic pyrochlore phase (Pb₂Ti₂O₆, Fd3m) was identified by XRD and Raman spectroscopy up to approx. 450°C. Only tetragonal PbTiO₃ was identified at higher temperatures. XAS spectra showed that the local structure around the absorbing Ti atom of the intermediate pyrochlore phase is similar to that observed in the amorphous precursor. This fact indicates that the metastable intermediate pyrochlore (Pb₂Ti₂O₆) is kinetically favored to be formed because of its similarity to the amorphous precipitate, instead of the slightly different and thermodynamically favored tetragonal (PbTiO₃, P4/mmm) perovskite structure that is only formed at higher temperatures, after the crystallization of the metastable intermediate pyrochlore.     

溶剂热还原法制备蛋壳状碳材料

Eggshell-like carbon materials with high yields have been synthesized by a solvothermal route in a stainless steel autoclave using metallic zinc and absolute ethanol as starting materials. The products were characterized by X-ray powder diffractometry (XRD)， energy-dispersive X-ray spectroscopy (EDX)， Raman spectroscopy and scanning electron microscopy (SEM). The eggshell-like carbon spheres had diameters ranging from 500 nm to 1 μm. The optimal reaction conditions to obtain eggshell-like carbon materials were 600 ℃ and 12 h.     

火焰原子吸收法测定铅锌矿中微量镓

将样品中的硫化物用HNO3氧化为硫酸盐后，再用HNO3、HF、H2SO4进一步溶解，在6mol/LHCl介质中用乙酸丁酯萃取镓，水反萃取后，用火焰析子吸收法测定Ga，该法检出限为0．80μg/mL，相对标准偏差为2．1％，用该法测得国家一级标准品的结果均与推荐值相符。     

Determination of gallium by extraction and atomic absorption measurement

Summary Gallium can satisfactorily be determined by atomic absorption in organic solvents using air-acetylene or nitrous oxide-acetylene flame. It is recommandable to extract it as chloride complex. By employing MIBK and nitrous oxide-acetylene flame a considerable increase of absorption signal and sensitivity and elimination of the interference effect of a large number of metal ions was achieved.

---

Bestimmung von Gallium durch Extraktion und Atomabsorptionsmessung

Zusammenfassung Mit Hilfe der Luft/Acetylen- oder N₂O/Acetylen-Flamme kann Ga aus organischen Lösungsmitteln mit guten Ergebnissen bestimmt werden. Zu bevorzugen ist die Extraktion als Chloridkomplex, Extraktion mit MIBK und Verwendung der N₂O-Acetylen-Flamme. So kann eine wesentliche Zunahme des Absorptionssignals, eine Verbesserung der Empfindlichkeit und Ausschaltung des störenden Einflusses zahlreicher Fremdionen bewirkt werden.

     

Preparation of nitrogen doped zinc oxide nanoparticles and thin films by colloidal route and low temperature nitridation process

Nitrogen doped zinc oxide (ZnO) nanoparticles have been synthesized using a colloidal route and low temperature nitridation process. Based on these results, 200 nm thick transparent ZnO thin films have been prepared by dip-coating on SiO₂ substrate from a ZnO colloidal solution. Zinc peroxide (ZnO₂) thin film was then obtained after the chemical conversion of a ZnO colloidal thin film by H₂O₂ solution. Finally, a nitrogen doped ZnO nanocrystalline thin film (ZnO:N) was obtained by ammonolysis at 250 °C. All the films have been characterized by scanning electron microscopy, X-ray diffraction, X-Ray photoelectron spectroscopy and UV–Visible transmittance spectroscopy.     

Preparation and pyrolysis of a blended precursor possessing Ti?N and Al?N bonds

The preparation and pyrolysis of a blended precursor possessing Ti? N and Al? N bonds were investigated. The precursor was prepared by mixing (HAlN ⁱPr) _n, whose main compo‐nent was a cage‐type compound, and an aminolysis product of Ti(NMe₂)₄ with MeHNCH₂CH₂NHMe with a molar ratio of Ti:Al = 2:1. IR analysis of the products pyrolyzed under NH₃–N₂ indicated that a large proportion of the organic groups in the precursor were removed by an amine‐exchange reaction during the pyrolysis under NH₃; thus, the products contained only a small amount of carbon. On the contrary, a considerable amount of carbon was present in the product pyrolyzed under Ar. Composites consisting of AlN and an NaCl‐type compound were obtained after pyrolysis of the precursor under both NH₃–N₂ and Ar. The composition of the NaCl‐type compound depended significantly on the pyrolysis atmosphere. Copyright © 2001 John Wiley & Sons, Ltd.     

Synthesis of ultraviolet luminescent turbostratic boron nitride powders via a novel low-temperature, low-cost, and high-yield chemical route

A novel chemical route has been established for the synthesis of ultraviolet luminescent turbostratic boron nitride (t-BN) powders, by the reaction of NH₄BF₄ with NaNH₂ at 320 °C for 10 h, and the yield is as high as 90%. The synthesized brown-yellow samples were characterized by XRD, XPS, FT-IR, SAED, and HRTEM, which matched with t-BN. The electronic and optical properties of the product were investigated by PL and UV absorption. UV spectra revealed that the product has two obvious band gaps (∼5.8 and 4.6 eV) and PL spectra showed that it has an ultraviolet emission at 337 nm (). SEM image indicated that the particle size of the synthesized t-BN is mainly in the range of 1-10 μm. The renascent BF₃ and Na₃N intermediates are believed to be responsible for the growth of t-BN under mild conditions.