Synthesis of the new layered oxides NaRbLnMO5 (Ln = La, Nd, Sm, Eu, Gd; M = Nb, Ta)

The new layered transition metal oxides NaRbLnMO₅ (Ln = Nd, Sm, Eu, Gd; M = Nb, Ta) were synthesized by direct solid-state reaction. NaRbLaNbO₅ crystallizes with a tetragonal unit cell [a=5.839(6) Å, c=8.313(1) Å] analogous to that of the related compound NaKLaNbO₅, while NaRbLaTaO₅ indexes to a larger monoclinic unit cell [a=9.577(2) Å, b=5.834(1) Å, c=8.323(2) Å, β=93.00(2)]. NaRbLnNbO₅ can be prepared for Ln = Nd, Sm, Eu, Gd, and NaRbLnTaO₅ can be prepared for Ln = Nd, Sm. Both series of compounds show the expected decrease in unit cell volume as the size of the lanthanide decreases. NaRbLaNbO₅ is also amenable to ion exchange, forming Li_2−xRb_xLaNbO₅ upon reaction with molten lithium nitrate.     

A facile method to prepare layered manganese oxides with large interplanar spacing

Layered manganese oxides with basal spacings up to 38.1 Å have been synthesized by a facile novel method in which cationic surfactant CTAB directly reacts with MnSO₄·H₂O and NaOH. The as-synthesized samples have expanded birnessite-type layered structures characterized by powder XRD and TEM. Synthetic parameters that are important to the formation and the basal spacing of the layered mesostructures are investigated, including the surfactant concentration, OH⁻/Mn²⁺ ratio, CTAB/Mn²⁺ ratio and aging time. Mechanisms based on self-assembling are discussed.     

Transformation of Dion-Jacobson phase to Aurivillius phase: synthesis of (PbBiO2)MNb2O7 (M = La, Bi)

We describe transformations of the Dion-Jacobson (D-J) phases, KLaNb₂O₇ and RbBiNb₂O₇, to the Aurivillius (A) phases, (PbBiO₂)LaNb₂O₇ (1) and (PbBiO₂)BiNb₂O₇ (2), in a metathesis reaction with PbBiO₂Cl. Oxide 1 adopts centrosymmetric tetragonal structure (a = 3.905(1) Å, c = 25.66(1) Å), whereas oxide 2 crystallizes in a noncentrosymmetric orthorhombic (A2₁am) (a = 5.489(1) Å, b = 5.496(2) Å, c = 25.53(1) Å) structure. Oxide 2 shows a distinct SHG response towards 1064 nm laser radiation. The role of La³⁺ versus Bi³⁺ in the perovskite slabs for the occurrence of noncentrosymmetric structure/ferroic property in these materials is pointed out.     

Synthesis and characterization of a mesoporous hydrous zirconium oxide used for arsenic removal from drinking water

Powder (20-50 μm) mesoporous hydrous zirconium oxide was prepared from a zirconium salt granular precursor. The effect of some process parameters on product morphology, porous structure and adsorption performance has been studied. The use of hydrous zirconium oxide for selective arsenic removal from drinking water is discussed.     

Rapid synthetic routes to prepare LiNi1/3Mn1/3Co1/3O2 as a high voltage, high-capacity Li-ion battery cathode material

LiNi_1/3Mn_1/3Co_1/3O₂, a high voltage and high-capacity cathode material for Li-ion batteries, has been synthesized by three different rapid synthetic methods, viz. nitrate-melt decomposition, combustion and sol–gel methods. The first two methods are ultra rapid and a time period as small as 15 min is sufficient to prepare nano-crystalline LiNi_1/3Mn_1/3Co_1/3O₂. The processing parameters in obtaining the best performing materials are optimized for each process and their electrochemical performance is evaluated in Li-ion cells. The combustion-derived LiNi_1/3Mn_1/3Co_1/3O₂ sample exhibits large extent of cation mixing (10%) while the other two methods yield LiNi_1/3Mn_1/3Co_1/3O₂ with cation mixing <5%. LiNi_1/3Mn_1/3Co_1/3O₂ prepared by nitrate-melt decomposition method exhibits superior performance as Li-ion battery cathode material.     

Synthesis and characterization of layered double hydroxides (LDHs) with intercalated chromate ions

Chromate intercalated layered double hydroxides (LDHs) having the formula M^II₆M′^III₂(OH)₁₆CrO₄·4H₂O (M^II = Ca, Mg, Co, Ni, Zn with M′^III = Al and M^II = Mg, Co, Ni with M′^III = Fe) have been prepared by coprecipitation. The products obtained are replete with stacking disorders. DIFFaX simulations show that the stacking disorders are of three kinds: (i) turbostratic disorder of an originally single layered hexagonal (1H) crystal, (ii) random intergrowth of polytypes with hexagonal (2H) and rhombohedral (3R) symmetries and (iii) translation of randomly chosen layers by (2/3, 1/3, z) and (1/3, 2/3, z) leading to stacking faults having a local structure of rhombohedral symmetry. IR spectra show that the CrO₄²⁻ ion is incorporated either in the T_d or in the C_3v symmetry. The interlayer spacing in the latter case is 7.3 Å characteristic of a single atom thick interlayer showing that the CrO₄²⁻ ion is grafted to the metal hydroxide slab. On thermal treatment, the CrO₄²⁻ ion transforms into Cr(III) and is incorporated into the spinel oxide or phase separates as Cr₂O₃. In the LDH of Mg with Al, Cr(III) remains in the MgO lattice as a defect and promotes the reconstruction of the LDH on soaking in water. In different LDHs, 18-50% of the CrO₄²⁻ ion is replaceable with carbonate anions showing only partial mineralization of the water-soluble chromate. The extent of replaceable chromates depends upon the solubility of the corresponding LDH, which in turn is determined by the solubility of the MCrO₄. These studies have profound implications for the possible use of LDHs for chromate amelioration in green chemistry.     

Synthesis and characterization of the new layered perovskite, Na0.10(VO)0.45LaTiO4·nH2O

Na_0.10(VO)_0.45LaTiO₄·nH₂O (n ≅ 0.6) has been synthesized by an ion exchange reaction between the single-layered perovskite, NaLaTiO₄, and aqueous VOSO₄. This low temperature phase retains the structure of the parent with a slight contraction of its tetragonal unit cell. Rietveld refinement of X-ray powder diffraction data indicate that the vanadyl units are disordered within the perovskite layers. Infrared spectroscopy, electron spin resonance and magnetic susceptibility are consistent with the presence of isolated vanadyl units. Susceptibility data show Curie-Weiss behavior above 140 K.     

Synthesis of PbTe thermoelectric materials by alkaline reducing chemical routes

Binary PbTe thermoelectric compounds have been successfully synthesized by alkaline reducing solvothermal, hydrothermal and low-temperature aqueous chemical routes using Pb(CH₃COO)₂·3H₂O and pure tellurium as precursors, and NaBH₄ as the reductant. Compared to PbTe powders synthesized by solvothermal and hydrothermal routes, smaller PbTe nanopowders of about 20 nm have been obtained by low-temperature aqueous chemical route. Possible formation mechanisms of PbTe were discussed.     

Oxidizing synthesis of Ni–Mn layered double hydroxide with good crystallinity

Ni²⁺–Mn³⁺ layered double hydroxide (LDHs) with good crystallinity and uniform morphology has been hydrothermally synthesized at 180 °C for 2 days using urea as hydrolysis agent and ammonium peroxodisulfate as oxidant. The obtained Ni²⁺–Mn³⁺ LDHs material has been characterized by XRD, SEM, XPS, FT-IR, and TG–DTA. Ammonium peroxodisulfate as oxidant plays an important role for the formation of Ni²⁺–Mn³⁺ CO₃²⁻ LDHs material, and Mn²⁺ ions are oxidized into Mn³⁺ ones during the precipitation of Mn²⁺ ions, giving rise to layered hydroxide with the hydrotalcite structure. Ni²⁺–Mn³⁺ LDHs material with Ni/Mn molar ratio of 4 has a layered structure with a basal spacing of 0.739 nm. The morphology, size, and uniformity of the as-prepared materials connect with the hydrothermal treatment temperatures, and uniform and regular flowerlike spheres with a mean lateral size of 3.5 μm are observed for Ni²⁺–Mn³⁺ LDHs material with good crystallinity and uniform morphology.     

Synthesis of molybdenum disulfide (MoS2) for lithium ion battery applications

This paper reports the use of a rheological phase reaction method for preparing MoS₂ nanoflakes. The characterization by powder X-ray diffraction indicated that MoS₂ had been formed. High resolution electron microscopy observation revealed that the as-prepared MoS₂ nanoflakes had started to curve and partly form MoS₂ nanotubes. The lithium intercalation/de-intercalation behavior of as-prepared MoS₂ nanoflake electrode was also investigated. It was found that the MoS₂ nanoflake electrode exhibited higher specific capacity, with very high cycling stability, compared to MoS₂ nanoparticle electrode. The possible reasons for the high electrochemical performance of the nanoflakes electrodes are also discussed. The outstanding electrochemical properties of MoS₂ nanoflakes obtained by this method make it possible for MoS₂ to be used as a promising anode material.     

Gel- to -crystallite conversion technique for the syntheses of M-β/β″-alumina (M = Li, Na, K, Rb, Ca or Eu)

Various alkali and alkaline earths hydroxides are reacted with hydrated alumina gel Al₂O₃·nH₂O (80 < n < 120) in hydrophilic organic solvents to yield precursor(s) with metal cation entrapped in the matrix, with the general formula M_yAlO_y(OH)_3−y (where M = Li, Na, K, Rb, Ca and Eu). Depending on the cation, the precursor crystallizes as metal-inserted gibbsite or boehmite structure. The nature of the precursor depends on the size of the cation, and its concentration, solvent used, solvent/water ratio, etc. These precursors yield M-β/β″-alumina phase on calcination at elevated temperatures in the case of sodium, potassium and rubidium. In the case of lithium, LiAl₅O₈ (spinel) phase is obtained. While calcium and europium give rise to calcium hexaaluminate and EuAlO₃ (perovskite), respectively, on calcination. The need of metal ion-inserted-γ-alumina phase is emphasized in obtaining M-β/β″-alumina phase.     

Intercalation of Ru(II) tris (1,10-phenanthroline) complex in α- and γ-zirconium dihydrogen phosphate. Synthesis, thermal behaviour and X-ray characterization

Layered inorganic systems such as ion-exchangers (α- and γ-zirconium dihydrogen phosphate) already used as hosts for larger cations, were studied for the intercalation of Ru(II) tris (1,10-phenanthroline) complex into these host matrices. The uptake of the complex occurs using the batch method; the colour of the materials changes from white to brilliant orange; the highest ion uptake is obtained in the case of the γ-phase. The materials obtained are thermally stable up to ∼350 °C and the complex decomposition occurs in two (α-phase) or three (γ-phase) steps. The complex decomposition is complete at ∼700 °C and at 550 °C (respectively for α- and γ-Ru(II) materials). As can be seen from the X-ray patterns, the Ru(II) materials are still layered and show a new phase with an increase in the interlayer distance with respect to the starting materials. The hydrogen form is always present in the case of the α-materials; whereas, in the case of the γ-materials, it is present when ≤0.12 moles of the complex/mole of exchanger are inserted. Microanalysis measurements confirm the fact that the Ru(II) complex is not modified when exchanged.     

Synthesis and characterization of a new layered magnesium zinc phosphate hydrate

A new layered magnesium zinc phosphate hydrate, MgZn(HPO₄)₂·H₂O, with a zinc phosphate framework isostructural with the one of Na₂Zn(HPO₄)₂·4H₂O, was prepared by the direct ambient pressure and temperature reaction between zinc 2,4-pentanedionate, phosphoric acid and hexahydrated magnesium chloride. The as-prepared sample is monoclinic (a = 8.780(7) Å, b = 13.240(7) Å, c = 11.123(0) Å and β = 116.21(2)°). The prepared solid undergoes two thermal transformations when it is heated from 110 to 600 °C. The first transformation is due to the release of intercalated water molecules and the second one is due to the HPO₄²⁻ → P₂O₇⁴⁻ transition.     

Synthesis of layered sodium lanthanum selenide through ion exchange reactions

Layered hexagonal KLaSe2 (α-NaFeO₂-type) was synthesized using the reactive flux method and analyzed by powder XRD to determine its lattice constants (space group R-3m, a = 4.40508(5) Å, c = 22.7838(5) Å). NaLaSe₂, which normally crystallizes as a disordered rock salt structure with mixed Na+/La + 3 sites, was synthesized through a solid state ion exchange reaction at 585 °C from a 1:3 molar ratio mixture of KLaSe₂:NaI. The product of this reaction was hexagonally layered NaLaSe₂ (space group R-3m, a = 4.3497(3) Å, c = 20.808(2) Å) isostructural to KLaSe₂. This product was analyzed by comparison with members of the set of solid solutions Na_(1−x)K_(x)LaSe₂ to confirm that the extent ion exchange in this reaction was complete. Cubic (disordered) NaLaSe₂ was also reacted with KI to yield the poorly crystalline hexagonally layered product with the approximate formula Na_0.79K_0.21LaSe₂.     

Size-adjusted hollow Ag spheres fabricated through reducing Ag2O in situ

Hollow Ag spheres with tunable sizes in a range of 74–167 nm were fabricated using a two-step synthesis including the creation of solid Ag₂O particles and the reduction of these Ag₂O particles in situ. Ag nanoclusters were generated by the reduction of Ag₂O. Ag₂O particles were as scaffolds to create Ag spheres. Namely, the reduction of Ag₂O occurred firstly on the surface of the Ag₂O particles. The H₂ was generated due to the hydrolysis of borohydride ions. The diffusion of H₂ and the further reduction of Ag₂O particles resulted in the formation of a hollow part within Ag spheres. The average diameter of the hollow Ag spheres can be adjusted by varying the concentration of NaOH and NaBH₄, the kinds of solvent, and reaction temperature.     

Formation of tubular BaTiO3 nanoparticle assembly through the Kirkendall effect using Na2Ti3O7 nanowires as template

We report the solvothermal synthesis of tubular BaTiO₃ nanoparticle assembly in ethanol/water mixed solvent system using Na₂Ti₃O₇ nanowires as template. The obtained tubular BaTiO₃ nanoparticle assembly, with a straight interior shell, is constructed by nanoparticles with diameters of 150–400 nm on the outer surface. The tubular BaTiO₃ nanoparticle assembly retains the one-dimensional characteristic inherited from the precursor Na₂Ti₃O₇ nanowires during solvothermal process. The formation mechanism of the hollow interior of tubular BaTiO₃ nanoparticle assembly is deriving from nanoscale Kirkendall effect, and the growth of nanoparticles on the outer surface with different sizes is controlled by the Ostwald ripening process, resulting in larger meaning outer diameter.     

Low temperature preparation of nanocrystalline Sr0.5Ba0.5Nb2O6 powders using an aqueous organic gel route

Nano-sized Sr_0.5Ba_0.5Nb₂O₆ (SBN50) ceramic powders have been synthesized by an aqueous organic gel route. Homogeneous Sr-Ba-Nb precursor gels are prepared with Ba-EDTA, Sr-EDTA, and Nb-citrate complex as source of Sr, Ba, and Nb, respectively. Citric acid and ethylenediaminetetraacetic acid (EDTA) were used as the chelating agents. The structural variation of the SBN powder with annealing temperature was studied by TG-DTA, FT-IR and XRD. The precursor gel on calcination at 800 °C for 2 h produces a pure tungsten bronze SBN phase and the corresponding average particle size is 30-50 nm. The influences of the pH and the molar ratio of citric acid:Nb cation on the formation of homogeneous Sr-Ba-Nb precursor gels were also studied. The results show that a homogeneous Sr-Ba-Nb precursor gel with no precipitate is formed at pH 8 and the optimum molar ratio of citric acid and the metal cations is 3:1.     

Synthesis of silver nanoparticles in a polyvinylpyrrolidone (PVP) paste, and their optical properties in a film and in ethylene glycol

Silver nanoparticles were synthesized in a paste of polyvinylpyrrolidone formed after mixing PVP with acetone and a small volume of aqueous silver nitrate under magnetic stirring. A film made with the material was characterized by UV-vis spectroscopy. The obtained spectrum shows a single peak at 438 nm, arising from the surface plasmon absorption of silver colloids. This result clearly indicates that silver nanoparticles are embedded in PVP. When the pre-treated PVP-Ag colloid is dissolved in ethylene glycol, the UV-vis spectrum of the resulting dispersion shows an absorption peak at 433 nm, whose maximum absorption blue shifts to 416 nm after 18 days of agitation. The silver nanoparticles have an average particle size of 4.12 nm. Because the IR band assigned to the carbonyl group of the PVP shifts to longer wavelengths, the interaction of this polymer with silver nanoparticles seems to take place through the carbonyl oxygen.     

Preparation and characterization of nanometer-scale powders ceria by electrochemical deposition method

Ceria (CeO₂) nanoparticles of 10-30 nm in average particle size have been synthesized via electrochemical deposition method in cerium(III) chloride solution with an undivided cell as electrochemical cell and ethanol-acetylacetone as additives. X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transformation infrared spectroscopy (FT-IR) and thermal analysis (TG-DTA) are introduced to characterize the samples. The results indicate that the as-prepared powders after being treated at 650 °C are nanocrystalline with the cubic fluorite structure and the sphericity in shape. It is revealed that the size of ceria nanoparticles can be decreased effectively by adding the ethanol-acetylacetone solution. In addition, the possible formed mechanism of CeO₂ nanometer-scale powder. The role of additive is also investigated in this paper.     

Facile synthesis via a solvothermal route and characterization of Mg–Al layered double hydroxide (LDH) 3D micro–nano structures

Different Mg–Al layered double hydroxide (LDH) 3D micro–nano structures had been synthesized via a facile solvothermal method. By carefully controlling the fundamental experimental parameters, the morphologies of hexagonal nanoplates, rose-like micro–nano structures, chrysanthemum-like micro–nano structures, and spherical micro–nano structures have been efficiently obtained, respectively. And these micro–nano structures are formed from self-assembly of nanoplates in a spontaneous process in solvothermal system. It is also found that the concentration of the reactant and the dosage of CTAB have significant effects on the morphology of the products. The FT-IR spectra and thermal stability of the micro–nano structures were explored.