Solvothermal synthesis and characterisation of La1−xAxMnO3 nanoparticles

The synthesis of La_1−xA_xMnO₃ (A=Ca, Sr, Ba) nanoparticles in nonaqueous solvents has been studied. For this solvothermal procedure benzyl alcohol and acetophenone were chosen as reaction media. After this treatment in mild conditions a precipitate was obtained, which, however, can be annealed to the crystalline perovskite structure. Our results show that acetophenone is more suited to obtain the clean pervoskite phase than benzyl alcohol.     

Magnetically recoverable lanthanum hydroxide as an efficient catalyst for Aerobic Oxidative Conversions of primary alcohols to the nitriles

Herein we report a novel magnetically recoverable lanthanum hydroxide nanoparticles for oxidative synthesis of nitriles directly from corresponding alcohols with ammonia as nitrogen source. The procedure for the preparation and characterization of La(OH)₃/Fe₃O₄ magnetic nanoparticles were investigated and the scope and generality of the method was explored for a series of structurally diverse primary alcohols with electron‐donating and electron‐withdrawing groups. The best result was observed when 5 mol% of La with respect to the benzyl alcohol was used at reflux condition under O₂ atmosphere. The La(OH)₃/Fe₃O₄ magnetic nanoparticles could be easily isolated from the reaction mixture with an external magnet and reused at least 5 times without significant loss in activity.     

Microbial synthesis of gold nanoparticles: Current status and future prospects

Gold nanoparticles have been employed in biomedicine since the last decade because of their unique optical, electrical and photothermal properties. Present review discusses the microbial synthesis, properties and biomedical applications of gold nanoparticles. Different microbial synthesis strategies used so far for obtaining better yield and stability have been described. It also includes different methods used for the characterization and analysis of gold nanoparticles, viz. UV–visible spectroscopy, Fourier transform infrared spectroscopy, X ray diffraction spectroscopy, scanning electron microscopy, ransmission electron microscopy, atomic force microscopy, electron dispersive X ray, X ray photoelectron spectroscopy and cyclic voltametry. The different mechanisms involved in microbial synthesis of gold nanoparticles have been discussed. The information related to applications of microbially synthesized gold nanoparticles and patents on microbial synthesis of gold nanoparticles has been summarized.     

Morphology-controlled synthesis of nanostructured zinc hydroxide fluoride via a microwave-assisted ionic liquid route

Zinc hydroxide fluoride (Zn(OH)F) with multiform morphologies such as flower-like particles, pumpkin-like aggregates, and hollow orange-like aggregates are prepared by a microwave-assisted ionic liquid method. During synthesis, microwave irradiation accelerates the reaction rate and shortens the reaction time. 1-Butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF₄]) or 1-2-hydroxylethyl-3-methylimidazolium tetrafluoroborate ([C₂OHmim][BF₄]) is used as both reactant and template. Experimental results indicate that the morphology evolution of Zn(OH)F is mainly controlled by the concentration of zinc acetate solution. A possible mechanism underlying the formation of nanostructured Zn(OH)F with diverse morphologies is proposed. Furthermore, nanoporous ZnO is obtained by the thermal decomposition of as-prepared Zn(OH)F in air, and the morphology is well retained.     

Thermal plasma synthesis of nanotitania and its characterization

Titanium dioxide (TiO₂) nanoparticles were prepared by the thermal plasma synthesis; which give a highly crystalline product. Their morphological studies are carried out by using techniques like SEM, EDAX, TEM and SEAD. Crystal size was calculated by XRD using Scherrer equation; which is observed at two current amperes; at 80 A size ranges between 25 and 30 nm and at 120 A size ranges between 30 and 42 nm. Composition analysis was done by TEM–EDAX, FTIR and Fast Fourier Transform techniques. The FTIR peaks clearly show that synthesized TiO₂ nanoparticles are in anatase phase; this phase is generally preferred because of its high photocatalytic activity, since it has a more negative conduction band edge potential (higher potential energy of photogenerated electrons), high specific area, nontoxic, photochemically stable and relatively in expensive.     

New nano-particle La(III) supramolecular compound as a precursor for preparation of lanthanum oxybromide-, hydroxide-, and oxide-nanostructures

Nano-particles of a new La(III) supramolecular compound [La(4,4′-bipy)(H₂O)₂(NO₃)_3.75Br_0.25] · (4,4′-Hbipy) (1), have been synthesized from reaction of 4,4′-bipy with La(NO₃)₃ and NaBr by the sonochemical method. For the first time LaOBr, La(OH)₃ and La₂O₃ nano-structures were prepared from [La(4,4′-bipy)(H₂O)₂(NO₃)_3.75Br_0.25] · (4,4′-Hbipy) (1) by calcination at 400, 500, and 700°C, respectively. The structure of 1 was determined by X-ray crystallography and the nano-structures were characterized by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). Thermal stabilities of nano and crystal samples of 1 were studied and compared with each other.     

Exploring the Cu‐In‐S System under Solvothermal Conditions near the Composition CuIn5S8

Solvothermal syntheses of copper‐indium‐sulfides performed with different Cu:In:S ratios afforded crystallization of nanocrystalline Cu‐In‐S phases with compositions close to CuInS₂, CuIn₃S₅, and CuIn₇S₁₁. Each sample shows a different and distinguishable morphology. The minority component CuInS₂ with wurtzite‐type structure crystallizes as thin plates, which are preferably stacked parallel to black stacks. The component with composition CuIn₃S₅ forms isolated few nm thin layers being arranged like the petals of a flower growing from a common point. Finally, red CuIn₇S₁₁ is obtained as nanobelts with individual diameters of about 20 nm and lengths up to more than 1 μm. According to electron diffraction patterns and X‐ray diffractometry the structures of CuIn₃S₅ and CuIn₇S₁₁ cannot be assigned to known bulk phases of the Cu‐In‐S system, however first structure models are proposed.     

Rapid one-step synthesis, characterization and functionalization of silica coated gold nanoparticles

This paper describes a rapid, simple and one-step method for preparing silica coated gold (Au@SiO₂) nanoparticles with fine tunable silica shell thickness and surface functionalization of the prepared particles with different groups. Monodispersed Au nanoparticles with a mean particle size of 16 nm were prepared by citrate reduction method. Silica coating was carried out by mixing the as prepared Au solution, tetraethoxysilane (TEOS) and ammonia followed by microwave (MW) irradiation. Although there are several ways of coating Au nanoparticles with silica in the literature, each of these needs pre-coating step as well as long reaction duration. The present method is especially useful for giving the opportunity to cover the colloidal Au particles with uniform silica shell within very short time and forgoes the use of a silane coupling agent or pre-coating step before silica coating. Au@SiO₂ nanoparticles with wide range of silica shell thickness (5-105 nm) were prepared within 5 min of MW irradiation by changing the concentration of TEOS only. The size uniformity and monodispersity were found to be better compared to the particles prepared by conventional methods, which were confirmed by dynamic light scattering and transmission electron microscopic techniques. The prepared Au@SiO₂ nanoparticles were further functionalized with amino, carboxylate, alkyl groups to facilitate the rapid translation of the nanoparticles to a wide range of end applications. The functional groups were identified by XPS, and zeta potential measurements.     

Nonaqueous synthesis of metal oxide nanoparticles: Short review and doped titanium dioxide as case study for the preparation of transition metal-doped oxide nanoparticles

The liquid-phase synthesis of metal oxide nanoparticles in organic solvents under exclusion of water is nowadays a well-established alternative to aqueous sol–gel chemistry. In this article, we highlight some of the advantages of these routes based on selected examples. The first part reviews some recent developments in the synthesis of ternary metal oxide nanoparticles by surfactant-free nonaqueous sol–gel routes, followed by the discussion of the morphology-controlled synthesis of lanthanum hydroxide nanoparticles, and the presentation of structural peculiarities of manganese oxide nanoparticles with an ordered Mn vacancy superstructure. These examples show that nonaqueous systems, on the one hand, allow the preparation of compositionally complex oxides, and, on the other hand, make use of the organic components (initially present or formed in situ) in the reaction mixture to tailor the morphology. Furthermore, obviously even the crystal structure can differ from the corresponding bulk material like in the case of MnO nanoparticles. In the second part of the paper we present original results regarding the synthesis of dilute magnetic semiconductor TiO₂ nanoparticles doped with cobalt and iron. The structural characterization as well as the magnetic properties with special attention to the doping efficiency is discussed.     

The synthesis of apatites with an organophosphate and in nonaqueous media

The syntheses of barium, cadmium, calcium, lead, and strontium apatites were performed in anhydrous polar organic solvents such as DMSO, anisole, pyridine, glacial acetic acid, ethanol, methanol, and DMF. Reactions took place under anhydrous conditions at temperatures ranging from 80 to 120 °C and for durations of 1–6 days. Ten apatites were synthesized in nonaqueous solvents and three (PbApF, PbApCl, SrApCl) were obtained using trimethylphosphate as the phosphate source. The use of nonaqueous solvents alleviates the formation of hydrogen phosphates which occurs in aqueous solution for some divalent cations. The limited solubility of even alkali metal salts in many of the solvents also produces nonapatitic double salts such as NaPb₄(PO₄)₃, NaPbPO₄, KPb₄(PO₄)₃, Cd(OH)NO₃, and NaBaPO₄.     

Organic reaction pathways in the nonaqueous synthesis of metal oxide nanoparticles

Nonaqueous-solution routes to metal oxide nanoparticles are a valuable alternative to the known aqueous sol-gel processes, offering advantages such as high crystallinity at low temperatures, robust synthesis parameters and ability to control the crystal growth without the use of surfactants. In the first part of the review we give a detailed overview of the various solution routes to metal oxides in organic solvents, with a strong focus on surfactant-free processes. In most of these synthesis approaches, the organic solvent plays the role of the reactant that provides the oxygen for the metal oxide, controls the crystal growth, influences particle shape, and, in some cases, also determines the assembly behavior. We have a closer look at the following reaction systems in this order: 1) metal halides in alcohols, 2) metal alkoxides, acetates, and acetylacetonates in alcohols, 3) metal alkoxides in ketones, and 4) metal acetylacetonates in benzylamine. All these systems offer some peculiarities with respect to each other, providing many possibilities to control and tailor the particle size and shape, as well as the surface and assembly properties. In the second part we present general mechanistic principles for aqueous and nonaqueous sol-gel processes, followed by the discussion of reaction pathways relevant for nanoparticle formation in organic solvents. Depending on the system several mechanisms have been postulated: 1) alkyl halide elimination, 2) elimination of organic ethers, 3) ester elimination, 4) C--C bond formation between benzylic alcohols and alkoxides, 5) ketimine and aldol-like condensation reactions, 6) oxidation of metal nanoparticles, and 7) thermal decomposition methods.     

Hydrothermal synthesis of precursors of neodymium oxide nanoparticles

The nanometric precursors of neodymium oxide of various morphologies were prepared via a hydrothermal reaction route. The precursors and their thermal evolution to neodymium oxide phase were characterised by means of X-ray diffraction (XRD), transmission electron microscopy (TEM, HRTEM), thermal analysis (TG, DTA, EGA-MS), FTIR and atomic force microscopy (AFM). It was found that the reaction conditions (temperature, pressure) played a key role for the product formation of desired morphology and structure. At mild conditions (140 °C) precursor with unusual fibrous morphology and Nd(OH)_2.45(Ac)_0.550.45H₂O stoichiometry was obtained. Upon heating this phase transformed, via intermediate cubic oxide, into trigonal Nd₂O₃ at 800 °C. Nd(OH)₃ hydroxide obtained at severe conditions (180 °C) transformed upon heating into cubic Nd₂O₃ phase at about 500 °C and this phase was stabilised even at 800 °C. The fibrous precursors appeared to be a convenient material for preparation of homogeneous thin coatings on planar substrates is shown.     

Structural study of lanthanum nickelate thin films deposited on different single crystal substrates

Fabrications of La₂NiO_4+δ thin film layers by liquid-injection metalorganic chemical vapor deposition were tried on different single crystals substrates: (001)Si, (001)MgO, (001)LaAlO₃ and (001)SrTiO₃. As results of structural characterizations, polycrystalline dendritic layers of La₂NiO_4+δ tetragonal (or orthorhombic) phase were observed on (001)Si substrates while layers of a perovskite-like cubic structure were observed on the other single crystal substrates. From a high-resolution TEM study of a layer deposited on (001)MgO, such a perovskite-like cubic structure exhibits many planar structural faults likely similar to planes of oxygen vacancies of the La₂NiO_4+δ orthorhombic structure. A thin intermediate epitaxial layer of NiO phase was also identified. Using a X-ray texture diffractometer, the layer structure on (001)MgO, (001)LaAlO₃ and (001)SrTiO₃ was confirmed to be of cubic structure with 〈100〉 axes parallel to those of the substrate. The T dependence of the resistivity of a layer deposited on (001)MgO substrate was found to be of a semi-conducting behavior.     

Solvothermal Synthesis,Crystal Structure and Properties of a New Organic Templated Lanthanum Sulfate [C4N3H16][La(SO4)3(H2O)]

A new organic templated lanthanum sulfate [C₄N₃H₁₆][La(SO₄)₃(H₂O)] ( 1 ) has been solvothermally synthesized by using n‐butanol as solvent. The colorless block crystals were characterized by IR, TGA, ICP, and XRD. The structure was determined by single‐crystal X‐ray diffraction: Monoclinic, P2₁/c, a = 10.8878(19), b = 15.478(3), c = 9.9639(18) Å, β = 114.062(2)°, V=1533.2(5) ų, Z = 4]. Crystal structure analysis shows that the one dimensional chain of 1 consists of the LaO₉ polyhedra and the sulfate groups. Coordination water molecules link adjacent chains by using hydrogen bonds to generate 2D layers, whereas the organic amines are inserted between the layers. The formation of 1 demonstrates that solvents play an important role during the synthesis.     

Fine tuning of gadolinium doped ceria electrolyte nanoparticles via reverse microemulsion process

Gadolinium doped ceria (Gd–CeO₂) nanoparticles have been synthesized by an reverse microemulsion system using cyclohexane as the oil phase, a non-ionic surfactant Igepal CO 520 and their mixed aqueous solutions of gadolinium III nitrate hexahydrate and cerium III nitrate hexahydrate as the water phase. The control of particle size was achieved by varying the water to surfactant molar ratio. The synthesized and calcined powders were characterized by thermogravimetry-differential thermal analysis (TGA-DTA), X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. The XRD results show that all the samples calcined at 700 °C were single phase cubic fluorite structure. The average size of the particle was found to increase with increase in water to surfactant molar ratio (R). The mean diameter of the particle for various value of R varies between 8–15 nm (SEM) and 7.5–11 nm (TEM), respectively. EDS confirm the presence of gadolinia and ceria phase in the nanopowder calcined at 700 °C. FTIR analysis was carried to monitor the elimination of residual oil and surfactant phases from the microemulsion-derived precursor and calcined powder. Raman spectroscopy and DTA evidenced the formation of a solid solution of gadolinium doped ceria at room temperature.     

Voltammetric determination of glucose based on reduction of copper(II)–glucose complex at lanthanum hydroxide nanowire modified carbon paste electrodes

A novel voltammetric method for the determination of β-d-glucose (GO) is proposed based on the reduction of Cu(II) ion in Cu(II)(NH₃)₄²⁺–GO complex at lanthanum(III) hydroxide nanowires (LNWs) modified carbon paste electrode (LNWs/CPE). In 0.1 mol L⁻¹ NH₃·H₂O–NH₄Cl (pH 9.8) buffer containing 5.0 × 10⁻⁵ mol L⁻¹ Cu(II) ion, the sensitive reduction peak of Cu(II)(NH₃)₄²⁺–GO complex was observed at −0.17 V (versus, SCE), which was mainly ascribed to both the increase of efficient electrode surface and the selective coordination of La(III) in LNW to GO. The increment of peak current obtained by deducting the reduction peak current of the Cu(II) ion from that of the Cu(II)(NH₃)₄²⁺–GO complex was rectilinear with GO concentration in the range of 8.0 × 10⁻⁷ to 2.0 × 10⁻⁵ mol L⁻¹, with a detection limit of 3.5 × 10⁻⁷ mol L⁻¹. A 500-fold of sucrose and amylam, 100-fold of ascorbic acid, 120-fold of uric acid as well as gluconic acid did not interfere with 1.0 × 10⁻⁵ mol L⁻¹ GO determination.     

Mono-cyclopentadienyl complexes of lanthanum: synthesis and characterization of anilido derivatives

Use of the bulky cyclopentadienyl ligand [η⁵-C₅H₂(SiMe₃)₃-1,2,4]⁻ (Cp?) allows for the isolation of monomeric, mono-ring lanthanide species. As previously reported, (Cp?)K reacts with LaI₃(THF)₄ (THF=tetrahydrofuran) in THF/pyridine to form the mono-ring complex (Cp?)LaI₂(py)₃ (1) (py=pyridine); a minor product of this reaction is the bis-ring species (Cp?)₂LaI(py) (2). The solid state structure of 2 reveals a monomeric compound containing a pseudo-tetrahedral metal center exhibiting no unusual intramolecular contacts. Addition of one equiv of KNHAr (Ar=2,6-ⁱPr₂C₆H₃) to complex 1 in THF generates the mono-anilido compound (Cp?)LaI(NHAr)(THF)₂ (3), which may be converted to the more stable pyridine adduct (Cp?)LaI(NHAr)(py)₂ (4) by the addition of pyridine to 3. An X-ray crystal structure of 3 indicated a trigonal bipyramidal metal center with the anilido group oriented trans to the iodide atom (N1-La1-I1=123.1(3)°). A structural study on the bis-pyridine adduct 4 revealed a similar C_s-symmetric structure with a slightly increased N_anilido-La-I angle of 132.1(2)°. Addition of KNHAr to the di-iodo bipyridine adduct (Cp?)LaI₂(bipy)(py) (5), in which the two iodide atoms are cis-disposed, yields the mono-anilido complex (Cp?)LaI(NHAr)(bipy)(py) (6) (bipy=2,2^′-bipyridine); this compound may also be prepared by the addition of bipy to (Cp?)LaI(NHAr)(py)₂ (4). An X-ray diffraction study shows that the lanthanum center in 6 is octahedrally coordinated by a Cp? ring, an iodide, an anilido group, a pyridine molecule and two nitrogens of a bipy molecule. In this case, the anilido moiety and the iodide ligand are arranged in a cis fashion (N_anilido-La-I=111.2(2)°), resulting in a complex with C₁ symmetry. Both (Cp?)LaI(NHAr)(py)₂ (4) and (Cp?)LaI(NHAr)(bipy)(py) (6) are inactive as catalysts for the hydroamination/cyclization of 2-amino-hex-5-ene.     

Controllable synthesis of zinc-substituted alpha- and beta-nickel hydroxide nanostructures and their collective intrinsic properties

A new controllable homogeneous precipitation approach has been developed to synthesize zinc-substituted nickel hydroxide nanostructures with different Zn contents from a zinc nanostructured reactant. As typical layered double hydroxides (LDHs), zinc-substituted nickel hydroxide nanostructures can be formulated as NiZnx(Cl)y(OH)2(1+x)-y.z H2O (x=0.34-0.89, y=0-0.24, z=0-1.36). The structure and morphology of zinc-substituted nickel hydroxide nanostructures can be systematically controlled by adjustment of the zinc content. The effects of temperature and the amounts of ammonia and zinc nanostructured precursor on the reaction were systematically investigated. In our new method, although zinc-substituted alpha-and beta-nickel hydroxides have the typical 3D flowerlike architecture and stacks-of-pancakes nanostructures, respectively, their growth processes are different from those previously reported. A coordinative homogeneous precipitation mechanism is proposed to explain the formation process of zinc-substituted nickel hydroxide nanostructures. The zinc-substituted nickel hydroxide nanostructures exhibit some interesting intrinsic properties, and changing the zinc content can effectively tune their optical, magnetic, and electrical properties.