Phase‐manipulable synthesis of Cu‐based nanomaterials using ionic liquid 1‐butyl‐3‐methyl‐imidazole tetrafluoroborate

Using the ionic liquid (IL), 1‐butyl‐3‐methyl‐imidazole tetrafluoroborate, and the precursor Cu₇Cl₄(OH)₁₀·H₂O, series of phase‐manipulable Cu‐based nanomaterials were synthesized by hydrothermal and microwave assisted routes, respectively. The structural characters of the as‐prepared CuO, CuO/Cu₂O composites and pure Cu nanoparticles were investigated by XRD, SEM, TEM and HRTEM, and their surface photovoltaic properties were studied by surface photovoltage spectra. Via hydrothermal route Cu²⁺ ions were found to be reduced gradually into Cu⁺ and subsequently Cu⁰ with increasing the IL, and various phase ratio of CuO, Cu₂O and Cu composite nanosheets and pure Cu nanoparticles were obtained. This implies that the IL could function as both a reductant in the oxygen‐starved condition and a template for the nanosheet products. The ¹H‐NMR result of the IL supports it being a reductant. In microwave assisted route, however, only monoclinic single crystalline CuO nanosheets were obtained, which indicates the IL being a template only in oxygen‐rich condition. Therefore, the crystal phase, composition and morphology of the Cu‐based products could be controlled by simply adjusting the quantity of the IL and oxygen in solution routes. The molecular structure of the IL after oxidation reactions was investigated by ¹H‐NMR and a possible reaction mechanism was proposed. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Graphene oxide used as a surfactant to induce the flower‐like ZnO microstructures: growth mechanism and enhanced photocatalytic properties

In this paper, graphene oxide (GO) was used as a temple to induce the formation of flower‐like ZnO microparticals compared with surfactants, such as cetyltrimethylammonium bromide (CTAB) and dodecyl dimethyl betaine (BS‐12). The zinc hydroxide carbonate ((Zn₄(CO₃)(OH)₆,ZHC)) was produced by a hydrothermal reaction. The flower‐like ZnO microparticals were gained by calcining ZHC. In the GO medium, the microparticals were assembled by numerous porous nanosheets from one point (initial nucleus) to flower‐like microparticals finally. The nanosheets of graphene oxide and functional groups were likely to contribute to the formation of the precursor, and some nanosheets were retained in the complex. The growth mechanism of ZHC was also proposed in this paper. The photocatalytic activity of the flower‐like ZnO microparticals was evaluated by photo degradation reaction of rhodamine B (RhB). The peony‐like porous ZnO/rGO compounds showed high photocatalytic activity and better than ZnO microparticals formed in the CTAB and BS‐12. These results indicated that GO could be widely used as a surfactant to induce composite materials with special morphology and photoelectric properties, etc.     

Synthesis of ZnO nanostructures composed of nanosheets with controllable morphologies

ZnO nanostructures composed of nanosheets have been synthesized by a facile low temperature reaction of Zn(OH)₂ and NaOH without the aid of any organic molecular templates. The influences of the reaction parameters, such as the concentrations of Zn(NO₃)₂, reaction temperatures, and reaction time on the morphologies of ZnO have been investigated. The thickness of ZnO nanosheets can be adjusted from 10–20 nm to 30–40 nm by altering the reaction temperatures from 80 °C to 180 °C. ZnO nanosheets are single crystals and the growth direction is perpendicular to [1100]. A possible gradual nucleation – rapid growth formation mechanism of ZnO nanosheets is proposed. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Facile synthesis of ultrathin NbTe2 nanosheets for enhanced tribological properties as a lubricant additive

Graphite‐like bulk NbTe₂ powders were prepared by a facile solid phase synthesis process and ultrathin NbTe₂ nanosheets were obtained by using wet ball milling induced delamination. The X‐ray diffraction analysis illustrated that the reduction of particle size was mainly along the stacking direction of the basal planes without great influence on the short range order of NbTe₂ crystals. Scanning electron microscopy, transmission electron microscopy, and atomic force microscope observations revealed that the longitudinal dimension of NbTe₂ samples changed into the nanoscale from the larger micron level after mechanical exfoliation. The exfoliated NbTe₂ nanosheets had better long‐term dispersion stability in paraffin oil than bulk NbTe₂. The tribological properties were determined on an UMT‐2 ball‐on‐disk friction and wear tester. The results indicated that the paraffin oil with NbTe₂ nanosheets exhibited better lubricating behaviors with the lower friction coefficient and wear rate in comparison with the bulk NbTe₂. It was demonstrated that NbTe₂ nanosheets could easily enter into a point of friction contact, and form an available tribofilm to prevent the direct contact between counterparts during the friction process. Furthermore, this work shows the potential applications of ultrathin NbTe₂ nanosheets in the field of tribology.     

Fast synthesis of Cu‐doped ZnO nanosheets at ambient condition

A new, fast and low cost method to produce Cu‐doped ZnO nanosheets is reported for the first time in this paper. Zinc foil specimens were immersed into CuSO₄ aqueous solutions with various concentrations for 3 seconds and then dried at ambient condition. The immersed specimens were characterized with a scanning electron microscope, an X‐ray diffractometer and a transmission electron microscope. The results show that Cu‐doped ZnO nanosheets with a multilayer structure on a cupper layer are formed. Cu‐doped ZnO nanosheets show hexagonal crystalline structure and comprises polycrystalline grains with diameters of 5∼10 nm. A physical modal is suggested to explain the prepared Cu‐doped ZnO nanosheet structure, based on the chemical reactions and a metallurgical cell.     

Synthesis on large area and uniform nanosheet morphology of polycrystalline cobalt oxide Co3O4 obtained from oxidation of Co films in a pure oxygen atmosphere

Large area and uniform nanosheets Co₃O₄ have been fabricated by thermal annealing of cobalt thin film under the DC magnetron sputtering method. The synthesis is based on controlling the simple thermal oxidative formation of precursor Co films. The Co films were heated at 300, 400, and 500 °C for two hours in a pure oxygen atmosphere. At 300 °C, CoO and Co₃O₄ phases appear to survive together. An amount of pure polycrystalline Co₃O₄ nanosheets were observed at 400 °C. The structural and morphological properties of the nanosheets Co₃O₄ were characterized by means of transmission electron microscopy (TEM) and Raman spectroscopy.     

Growth aspects of barium oxalate monohydrate single crystals in gel medium

Single crystals of barium oxalate monohydrate (BaC₂O₄.H₂O, BOM) were grown in pure form by controlled diffusion of Ba²⁺ using the gel technique at different temperatures. Starting from aqueous Ba²⁺ chloride (BaCl₂) and acetic acid (C₂H₂O₄) in gel, this method offers a low‐cost and an easiest alternative to other preparation methods for the production of barium oxalate bulky single crystals. The optimal conditions for the growth of BOM crystals in silica gel were found by investigating different growth parameters such as gel pH, gel aging and crystallization temperature. Irrespective of all such crystallization environments, growth rate of the crystals were initially less and then exhibited supersaturation effect leading to non‐linearity. Gel aging and temperature has profound effect on nucleation density that resulted less number of crystals of maximum size in the gel matrix. Perfect single crystals were grown on gels of higher pH. The macropore morphology and porosity was controlled by changing age of the gel. It has been found that temperature has a fabulous effect in controlling the nucleation density by altering the supersaturation conditions for the formation of critical nuclei. The entire growth kinetics informed that the grown crystals were derived by the one dimensional diffusion controlled process. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Novel mixed–solvothermal synthesis of MoS2 nanosheets with controllable morphologies

MoS₂ nanosheets with controllable morphologies were successfully synthesized via a novel mixed–solvothermal approach based on interfusing organic solvent in the solution. The morphology of the MoS₂ nanosheets was lamellar–like using the mixed water/ethanol/N–Methyl pyrrolidone solvents, whereas that prepared with the mixed water/ethano/ethylene glycol solvents changes to fullerene–like. Because of the structure‐directing ability of organic molecules, the mixed solvents were proposed to be responsible for the formation of such different morphologies. The average size of MoS₂ nanosheets was approximately 90 nm, and the thickness was about 10–20 nm. The results indicated that the crystalline phase and morphology were largely influenced by calcination and reaction system.     

Thermal and infrared studies of calcium malate crystals grown in diffusion limited medium

Single crystals of the title compound Ca (C₄H₅O₅)₂.10H₂O are grown in silica gel using controlled chemical reaction method. Multifaceted single crystals of size up to 8 × 4 × 2 mm³ are obtained. Powder X‐ray Diffraction (XRD) pattern of the grown crystal and the Fourier Transform Infra‐Red (FTIR) spectrum in the range 400–4000 cm^–1 are recorded. The vibrational bands corresponding to different functional groups are assigned. Thermal decomposition stages observed in the Thermo‐gravimetric (TG) and Differential Thermal Analysis (DTA) studies are discussed. A six‐stage thermal decomposition scheme is proposed for the compound. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal growth of zirconium‐doped KTiOPO4 crystals in the K2O‐P2O5‐TiO2‐ZrF4 system

Zirconium‐doped KTiOPO₄ (KTP) crystals were grown using a high temperature flux method in the K₂O‐P₂O₅‐TiO₂‐ZrF₄ system. The dopant content in the single crystals with general composition KTi_1‐xZr_xOPO₄ (where x = 0 – 0.026) strongly depends on zirconium concentration in the homogeneous melts. AES‐ICP method and X‐ray fluorescence analysis were used to determine the composition of the obtained crystals. Phase analyses of the products were performed using the powder XRD. The structures of KTiOPO₄ containing different quantities of Zr were refined on the basis of single crystal XRD data. Applying ZrF₄ precursor for zirconium injection into the flux allowed growing the zirconium‐doped KTP crystals at 930–750°C. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and characterization of ferroelectric‐ferroelastic Tb2(MoO4)3 crystals

Transparent and nearly colorless ferroelectric‐ferroelastic β′‐Tb₂(MoO₄)₃ (TMO) single crystals have been grown by the Czochralski (CZ) method. The single crystal structure was investigated by X‐ray powder diffraction and was shown to be a single phase with the structure similar as the β′‐Gd₂(MoO₄)₃ crystal. The optical transparency of the TMO crystal has been measured and the crystal is almost transparent in the visible and near infrared regions. The defects of TMO crystal were evaluated by etching technique and the ferroelectric domain structures were observed by an optical microscope. A high‐resolution X‐ray diffraction analysis demonstrates that the as‐grown TMO crystal possesses relatively high optical quality. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal growth and structure of KBi(WO4)2 single crystals

Potassium bismuth tungstate [KBi(WO₄)₂] single crystals have been grown by the top‐seeded solution growth technique. Bulk crystal with dimensions up to several centimeters is obtained for the first time. Several self‐flux systems have been used for the growth from the solution and the experiments using K₂W₂O₇ as a solvent are detailed. Powder and single crystal X‐ray diffraction of this crystal are reported. The structure refinement shows that KBi(WO₄)₂ crystallizes in the monoclinic space group C2/c, with a=10.837(3), b=10.586(3), c=7.622(2)Å, β=130.860(3)°, V=661.4(3)ų, and Z=4. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of the atmosphere on the growth of LiYF4 single crystal fibers by the micro‐pulling‐down method

Micro‐pulling‐down growth of LiYF₄ single crystal fibers have been performed under different gas atmospheres using stoichiometric LiYF₄ single crystal pieces from prior Czochralski experiments as starting material. Completely transparent and phase pure LiYF₄ single crystal fibers could be obtained after evacuation of the recipient to 2×10^‐6 mbar and subsequent filling with pure (99.995%) CF₄ gas. Using a gas mixture of 5% CF₄ in Argon or pure 5N Argon leads to the formation of micro crystallites of oxofluorides on the surface. Evacuating only to 3 × 10^‐3 mbar leads, independently of atmosphere, to completely white fibers that are heavily contaminated with oxofluorides. DSC measurements of the completely transparent fiber grown under pure CF₄ atmosphere reveal congruent melting behavior. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Flux growth of La‐doped lead zirconate stannate titanate antiferroelectric crystals

Relaxor antiferroelectric single crystals lead lanthanum zirconate stannate titanate (PLZST) with the composition around the morphotropic phase boundary (MPB) have been grown by flux method using 50 wt% PbO‐PbF₂‐B₂O₃ as a flux. The obtained crystals are light yellow in color. The XRD patterns revealed that the habitual faces of the obtained crystal are (001). The crystal morphology was studied and related to a layer growth mechanism controlled by two‐dimensional growth. The chemical composition of as‐grown crystal was analyzed by inductively coupled plasma atomic emission spectrometry (ICP), indicating a slight decrease of the amount of Ti compared to the starting materials. The result was verified by the XRD patterns with the phase transformation from the co‐existence of tetragonal and rhombohedra phases to the single tetragonal phase. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal Structure of RbD2PO4.D2O: A new Hydrate Phase of KDP‐type Compounds

The mono‐hydrate phase as well as the water‐free RbD₂PO₄ (DRDP) is obtained by crystal growth from fully deuterated aqueous solution. Its crystal structure was determined by combined neutron and X‐ray single crystal diffraction. It consists of double layers of PO₄ tetrahedra with D₂O planes in between. The PO₄ groups are linked by fully ordered deuterium bonds O‐D‐O. RbD₂PO₄.D₂O dehydrates below 329(5)K and undergoes a phase transition to RbD₂PO₄ (DRDP).     

Growth of ytterbium tartrate trihydrate crystals in silica and agar‐agar gels and their characterization

Single crystals of ytterbium tartrate trihydrate have been grown by gel method using silica and agar‐agar gels as media of growth. The medium of growth influences the morphology of grown crystals, silica gel yielding single and polycrystalline in the form of spherulites whereas agar‐agar gel leading to growth of single and twinned crystals. Materials grown as single crystals have been characterized by using optical and scanning electron microscopy (SEM), EDAX, XRD, FT‐IR, CHN and thermogravimetric techniques. The stoichiometry of the grown single crystals is suggested to be Yb(C₄H₄O₆) (C₄H₅O₆).3H₂O. The FT‐IR spectrum shows the presence of singly as well as doubly ionized tartrate ligands. Results of thermal analysis indicate that the material is thermally stable up to a temperature of 200 °C. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

White light emission materials of self‐assembled rare earth molybdates NaRe(MoO4)2 micro‐particles: the controllable synthesis,growth mechanism and luminescent properties

The tetragonally double alkaline rare earth molybdates NaRe(MoO₄)₂ (Re = Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, and Er) micro‐particles in aqueous solution of Re(NO₃)₃ and Na₂MoO₄ were prepared hydrothermally by a facile and effective EDTA‐assisted method, and investigated by XRD, SEM, FE‐SEM, photoluminescence (PL) excitation and emission spectra. The results showed that the radii of Re ions, pH and the molar ratio of Re(NO₃)₃/Na₂MoO₄ in the synthesis solution play an important role in controlling sizes, morphologies and luminescent properties of the final products. And the possible formation mechanism for the bipyramid‐like structure and role of EDTA were discussed in detail. The microstructure and PL property of NaY_xLa_1‐x(MoO₄)₂:10%Eu³⁺ was investigated, and it showed that NaY_0.5La_0.5(MoO₄)₂ exhibited regular sphere‐like morphology and emitted the stronger red emission with better color purity than other products. When Tm³⁺, Dy³⁺ and Eu³⁺ with appropriate concentrations were used as dopants to modify this bipyramid NaY(MoO₄)₂ material, the white light emission material of NaY(MoO₄)₂:1%Tm³⁺‐11%Dy³⁺‐0.6%Eu³⁺ was successfully synthesized and its CIE chromaticity coordinates is (0.33, 0.33), which is the standard white light point. These novel white‐light‐emitting NaY(MoO₄)₂:1%Tm³⁺‐11%Dy³⁺‐0.6%Eu³⁺ with single phase would be a promising material in the WLED field.     

The crystal and molecular structure of bis(tetramethylammonium) pentachlorooxomolybdate(V)‐acetonitrile(1:1)

The crystal structure of the title compound, C₁₀H₂₇Cl₅MoN₃O was determined by single crystal X‐ray diffraction technique. The crystals are monoclinic, space group C 2/m, with a= 29.075(8) Å, b= 11.843(4) Å, c= 13.252(4) Å, β=117.049(7)°, V = 4064(2) ų, Z=8. The structure was solved by direct methods and refined by least‐squares methods to a final R = 0.0307 for 5095 observed reflections with I>2σ(I). In the pentachlorooxomolybdate anion, the planar chlorines are bent away from the axial oxygen ligand. The Mo‐O bond length is 1.6620(18) Å that indicates significant double bond character. The oxygen trans Mo‐Cl bond is significantly longer than all of the planar Mo‐Cl bonds. These differences can be attributed to a trans influence of the oxygen atom. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Studies on the growth and optical characterization of dysprosium gadolinium oxalate single crystals

Preparation and optical characterization of dysprosium gadolinium oxalate (DGO) single crystal is reported. The crystals were grown using silica gel technique, by the controlled reaction of rare earth nitrates with oxalic acid. Crystals were characterized using X‐ray powder diffraction, optical absorption and fluorescence studies. Radiative transition probability, fluorescence branching ratio and radiative lifetime of Dy³⁺ in the crystal are evaluated by the parameterization of the absorption spectrum by the Judd‐Ofelt theory. The recorded fluorescence spectrum showed two well resolved peaks at 480 nm and 571 nm and are assigned to the transitions from ⁴F_9/2 → ⁶H_15/2 and ⁶H_13/2 of Dy³⁺. Stimulated emission crossection and optical gain of these transitions are also evaluated. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis of MoSe2/Reduced graphene oxide composites with improved tribological properties for oil‐based additives

In this work, we developed a facile and effective hydrothermal method synthesis of MoSe₂ nanoflowers on reduced graphene oxide (RGO) sheets. The as‐prepared MoSe₂/reduced graphene oxide (MoSe₂/RGO) composites are characterized by X‐ray diffractometer (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results indicated that MoSe₂ nanoflowers were successfully deposited on RGO nanosheets to form a well interconnected hybrid structure. The tribological properties of MoSe₂/RGO composites as lubricating oil additive were investigated by a UMT‐2 ball‐on‐plate friction and wear tester. By the addition of MoSe₂/RGO composites in paraffin oil, the antiwear ability was improved and the friction coefficient was decreased. The based oil with MoSe₂/RGO composites showed better tribological properties than the oil with MoSe₂ and pure oil. The good friction and wear properties of MoSe₂/RGO composites as additives were attributed to the formation of a thin physical tribofilm on the substrate.