Solvothermal synthesis of chalcopyrite CuIn0.7Ga0.3Se2 nanoparticles and the studies on reaction mechanism and structure defects

By using a solvothermal reaction in ethylenediamine, quaternary chalcopyrite CuIn_0.7Ga_0.3Se₂ nanoparticles have been successfully synthesized at 270 °C. The nanoparticles were characterized by XRD, XPS, TEM, HRTEM. The possible reaction mechanism was simply discussed. The size of nanoparticles ranged from 20 nm to 100 nm, being consistent with the calculated value. We observed point defects and planar defects by using TEM, and the possible formation mechanism was also discussed.     

Large-scale synthesis of ultralong Sb2S3 sub-microwires via a hydrothermal process

This paper describes an ethylene glycol (EG)-assisted approach to the large-scale ultralong Sb₂S₃ sub-microwires, formed by a simple hydrothermal reaction between SbCl₃ and Na₂S in the presence of distilled water. Transmission electron microscopy and scanning electron microscopy studies indicate that these Sb₂S₃ sub-microwires possess a diameter around 200 nm and length up to 100 μm. High-resolution transmission electron microscopy and selected area electron diffraction studies reveal that each Sb₂S₃ sub-microwire is a single-crystal along the [0 0 1] direction. The possible formation mechanism of the sub-microwires was discussed. The effects of volume ratio of EG/water, reaction temperature and the concentration of CO(NH₂)₂ on the morphology of Sb₂S₃ sub-microwires were also investigated.     

Tartarate precursors to CoxZn1−xGa2O4 spinel oxides

The Co_xZn_1−xGa₂O₄ spinels (x = 0.25, 0.5, 0.75, 1) were synthesized by a wet chemistry method–the precursor route via tartarate decomposition. The complex precursors have been characterized by IR, UV–Vis, magnetic measurements and luminescence spectroscopy. XRD, SEM, IR, UV–Vis and luminescence spectroscopy were used for the structural and morphological investigation of Co_xZn_1−xGa₂O₄ spinels; magnetic susceptibilities of the spinel were also measured. The X-ray diffraction patterns confirmed the formation of gallate spinel phase, Co_xZn_1−xGa₂O₄.     

Ligand-assisted hydrothermal synthesis of ZnWO4 rods and their photocatalytic activities

ZnWO₄ rods were prepared using a ligand-assisted hydrothermal method with ZnCl₂ and Na₂WO₄ in the presence of various amines as ligands for zinc ions. The choice of ligand was found to play an important role in the formation of ZnWO₄ rods. The aspect ratio of the ZnWO₄ rods increased with increasing ligand strength. XRD and HRTEM confirmed that the ZnWO₄ rods grow along the [1 0 0] direction. The photochemical activities of the ZnWO₄ rods for the decomposition of Rhodamine 6G were examined. The photocatalytic activity was found to depend on the aspect ratio of the ZnWO₄ rods.     

Fabrication of β-Si3N4 whiskers by combustion synthesis with MgSiN2 as additives

β-Si₃N₄ whiskers with diameter of 0.5–2 μm and aspect ratio of 10–15 have been successfully prepared by combustion synthesis under 30–50 atm nitrogen pressure. The addition of MgSiN₂ powder plays a significant role in the growth of β-Si₃N₄ whiskers. The as-prepared products were characterized by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM).     

Synthesis of nanocrystalline CeAlO3 by solution-combustion route

CeAlO₃ was synthesised by a modified solution-combustion route using a mixture of urea and glycine as fuel. A trivalent oxidation state of cerium was stabilised and high-quality single phase polycrystalline CeAlO₃ was obtained by optimising the ratio of fuels. The transmission electron micrography and powder X-ray diffraction investigations showed that the particles were nanocrystalline in nature. Rietveld refinement confirmed the space group of the structure to be I4/mcm$I4/mcm$ with lattice parameters a=5.3278(1)$a=5.3278(1)$ Å, c=7.5717(3)$c=7.5717(3)$ Å. Magnetisation measurements indicated that the sample was paramagnetic up to 2 K. The susceptibility data fitted the Curie–Weiss model in the temperature range 100–300 K with _θp=−40${\theta }_p=-40$ K. The value of _μeff=2.2_μB${\mu }_{\text{eff}}=2.2{\mu }_B$ was close to that expected for a Ce³⁺ ion. The magnetic properties were comparable to that reported for single crystals indicating the high quality of CeAlO₃ prepared in the present work. The semiconducting band gap as estimated from UV–visible spectroscopy was 3.26 eV.     

Mechanochemical synthesis of NaNbO3

The mechanochemical synthesis of NaNbO₃ is studied. It is shown that NaNbO₃ can be prepared by milling the constituents, i.e. Na₂CO₃ and Nb₂O₅ in the planetary mill. After 40 h of mechanochemical treatment NaNbO₃ nanoparticles in the range of 10-20 nm are obtained. Furthermore, the high-energy milling leads to the mechanochemically-triggered carbonate decomposition, which has been observed for a few cases in the open literature.     

Surfactant-free synthesis of Bi2WO6 multilayered disks with visible-light-induced photocatalytic activity

The synthesis of bismuth tungstate (Bi₂WO₆) multilayered disk which was constructed by oriented square nanoplates was easily realized via a simple surfactant-free hydrothermal method. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM) were used to investigate the as-obtained product. The results indicated that the three-dimensional (3D) Bi₂WO₆ multilayered disk was constructed by self-assembly of square nanoplates via a perfect oriented manner. The formation mechanism of the product was carefully investigated on the basis of the results of time-dependent experiments. In addition, studies of the photocatalytic property demonstrated that the as-obtained Bi₂WO₆ could exhibit excellent visible-light-driven photocatalytic activity for the degradation of Rhodamine B (RhB).     

Combustion synthesis of CuFe2O4

Metallic ferrites are investigated as prospective materials for different applications especially as anodes in extractive metallurgy. CuFe₂O₄, one of the important ferrites, is envisaged for substituting the carbon anode in Hall-Heroult cells. A single step combustion process has been used for the synthesis of CuFe₂O₄ powder from cupric nitrate, ferric nitrate and urea. The experimental conditions for maximum conversion efficiency of the precursor powders have been optimized. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) have confirmed the formation, structure and homogeneity of the as-prepared powders. The detailed physical, electrical and structural characterization of the materials have been carried out for the specimens obtained on sintering at different temperatures up to 1000 °C.     

Structural characterization of In2O3 hierarchical microwires synthesized through decomposition thermal treatment of InSe single crystal

In this paper, we report the obtention of In₂O₃ nanostructured microwires by the decomposition thermal treatment of InSe single crystal in two-steps under an oxygen–ammonia flow without the presence of any catalyst. Long In₂O₃ microwires with uniform shape and homogeneous surface were first synthesized through thermal treatment of InSe single crystal at temperature of about 640 °C; then, furnace temperature was increased to 750 °C and, as annealing time proceeded, the obtained microwires served as substrates on which nanorod branches grew. The shape and the structure of the microarchitectures were characterized by means scanning electron microscopy, transmission electron microscopy, selected area diffraction pattern, X-Ray diffraction and Raman spectroscopy. Our results indicated that In₂O₃ primary wires with a clean surface grew in the [100] direction and that the secondary protuberances grew in the [011] direction. A possible growth mechanism of the hierarchical microwires was also proposed.     

Synthesis and characterization of nanocrystalline MgAl2O4 spinel via sucrose process

Nanocrystalline MgAl₂O₄ spinel powder was synthesized using metal nitrates and a polymer matrix precursor composed of sucrose and polyvinyl alcohol (PVA). The precursor and the calcined powders were characterized by simultaneous thermal analysis (STA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). According to XRD results, the inceptive formation temperature of spinel via this technique was between 600 and 700 °C. The calcined powder at 800 °C for 2 h has faced shaped morphology and its crystallite size is in the range of 8-12 nm. Further studies also showed that the amount of polymeric matrix to metal ions has significant influence on the crystallite size of synthesized magnesium aluminate spinel powder.     

A mild solvothermal route to α-Fe2O3 nanoparticles

A mild solvothermal route has been developed to synthesize α-Fe₂O₃ nanoparticles using Fe(NO₃)₃ as a starting material. The results from XRD and TEM indicate the α-Fe₂O₃ powders possess a rhombohedrally centered hexagonal structure, and the size of particles from alcohothermal method at 160 °C is about 50-100 nm.     

Low temperature synthesis and characterization of SnTa2O6

Sn(II)Ta₂O₆ is well known as the mineral Thoreaulite, but attempts to prepare it by direct combination of SnO and Ta₂O₅ fail. SnTa₂O₆ has now been synthesized by reacting SnCl₂ with KTaO₃ at 673 K under an inert atmosphere. Although a reported structure determination of SnTa₂O₆ indicated an acentric space group, our second harmonic generation (SHG) studies indicate that SnTa₂O₆ is centrosymmetric as is the case for isostructural SnNb₂O₆.     

Synthesis of nanocrystalline Mn3O4 at 100 °C

A simple gel to crystal conversion route has been followed for the preparation of nanocrystalline tetragonal Mn₃O₄ powders at 80-100 °C under refluxing conditions. Freshly prepared manganese hydroxide gel is allowed to crystallize under refluxing and stirring conditions for 4-6 h. Formation of nano crystallites of Mn₃O₄ is confirmed by X-ray diffraction (XRD) study. Transmission electron microscope (TEM) investigations revealed that the average particle size is 50 nm for these powders.     

Photocatalytic activity of SnWO4 and SnW3O9 nanostructures prepared by a surfactant-assisted hydrothermal process

Flower-like α-SnWO₄ and rod-like SnW₃O₉ nanostructures in the form of a single and a mixed phase were prepared by hydrothermal process at 200 °C for 36 h in a wide pH range, with the assistance of dodecyltrimethylammonium bromide (DTAB). The effects of the pH of the synthesis solution and the Sn²⁺/W⁶⁺ molar ratio on phase compositions, structures and morphologies of the as-prepared powders were investigated. As a single phase, α-SnWO₄ and SnW₃O₉ could be hydrothermally prepared at pHs 7-8 and 1, respectively. In the form of a mixed phase, they could be hydrothermally obtained in the pH range of 2-6. The electron microscopy observations revealed that α-SnWO₄ powders presented flower-like structures with the diameter of 2-5 μm and SnW₃O₉ powders possessed rod-like structures with the width of 250 nm and the length of 2 μm. The X-ray photoelectron spectroscopy (XPS) results confirmed the reduction of tungsten from W⁶⁺ to W⁴⁺ during the hydrothermal process in accordance with the pH value. The UV-vis diffuse reflectance absorption spectra proved a strong visible-light absorbance of α-SnWO₄ powders in the range of 400-650 nm. Compared to phase-pure SnW₃O₉ and the mixture of α-SnWO₄ and SnW₃O₉ phases, phase-pure α-SnWO₄ exhibited a good photocatalytic activity for the degradation of methyl orange under visible-light irradiation. After several cycles, the α-SnWO₄ sample retains high degradation efficiency.     

Polyol mediated synthesis of nanocrystalline M3SbS3 (M=Ag, Cu)

A simple and convenient polyol-mediated route has been developed to produce nanocrystalline Ag₃SbS₃ and Cu₃SbS₃ from AgNO₃ and Cu(NO₃)₂ and SbCl₃ with thiourea at 197 °C. The products were characterized by X-ray powder diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. Analysis shows that glycol agitated state and injection rate have a great effect on the purity of the final products.     

Reflux synthesis and hydrothermal processing of ZrO2 nanopowders at low temperature

In this paper, we report on the reflux synthesis at 90 °C and hydrothermal processing at 120 °C for obtention of zirconium oxide (ZrO₂) nanopowders under several conditions. These nanopowders were characterized by X-ray diffraction (XRD), Fourier transform Raman (FT-Raman) spectroscopy, adsorption–desorption N₂-isotherms, Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA) and field-emission scanning electron microscopy (FE-SEM). XRD patterns and Raman spectra indicated that ZrO₂ nanopowders present a monoclinic structure. In addition, the hydrothermal processing promoted an increase in crystallinity of ZrO₂ nanopowders. FT-IR spectra revealed a small shoulder on the ν (Zr–O) bands in transmittance spectra of the ZrO₂ nanopowders. The decomposition of precursor was accompanied by evolution of TGA curves. The morphology of ZrO₂ nanopowders was observed by FEG-SEM. Also, the FEG-SEM micrographs revealed that the presence of H₂O₂ in systems reduced the particle size, while the absence of promoted an increase in particle size.     

Syntheses and structures of Ta2(WO2)0.87H0.26(PO4)4 and Ta2(MoO2)(PO4)4

Tantalum hydrogen phosphate, β-TaH(PO₄)₂, has a three-dimensional structure that is stable to remarkably high temperature (∼600 °C) presumably due to the presence of strong hydrogen bonds. Impedance measurements indicate a low conductivity, 2.0 × 10⁻⁶ S/cm at 200 °C in 5% H₂. In further studies aimed at enhancing the conductivity by aliovalent doping, we have investigated systematically the synthesis of compounds in the TaH(PO₄)₂-W₂P₂O₁₁ system at 380 °C. As a result, a new phase, Ta₂(WO₂)_0.87H_0.26(PO₄)₄, was identified and subsequently the molybdenum analog Ta₂(MoO₂)(PO₄)₄ was also prepared. The structures were determined by single crystal X-ray diffraction techniques. The structures of Ta₂(WO₂)_0.87H_0.26(PO₄)₄ and Ta₂(MoO₂)(PO₄)₄ can be formally derived from the structure of β-TaH(PO₄)₂ by the replacement of two P-OH protons with an MO₂²⁺ (M = Mo and W) group together with a change in the orientation of some phosphate tetrahedra.     

Large-scale synthesis of Mn11(HPO3)8(OH)6 superstructures constructed by microrods via a mixed-solvothermal route

In this paper, we reported the successful synthesis of hollow hemispherical Mn₁₁(HPO₃)₈(OH)₆ superstructures on a large scale via a facile mixed-solvothermal route without assistance of any surfactant, employing MnAc₂·4H₂O and NaH₂PO₂·H₂O as the reactants, the mixture of N,N-dimethylformamide (DMF) and water as the solvent. The reaction was carried out at 160 °C for 12 h. HPO₃²⁻ ions were provided via the dismutation reaction of H₂PO₂⁻ ions. The as-obtained product was characterized by X-ray powder diffraction (XRD), energy dispersive spectrometry (EDS) and field emission scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Some factors influencing the morphology of the hollow hemispherical Mn₁₁(HPO₃)₈(OH)₆ superstructures, such as the reaction temperature, time, the amount of NaH₂PO₂, and the volume ratio of DMF/water, were systematically investigated. A possible growth mechanism was proposed based on experimental results.