Low-temperature catalytic preparation of multi-wall MoS<Subscript>2</Subscript> nanotubes

In the catalytic reduction atmosphere of H₂+CH₄+C₄H₄S, the ball-milled precursor (NH₄)₂MoS₄ is heated to 300°C for decomposition. The as-synthesized product is characterized by XRD, SEM, HRTEM, EDX, and BET. The results show that multi-wall MoS₂ nanotubes are obtained. The length of the nanotubes is around 3–5 μm. The diameters of the nanotubes are homogeneous, with an inner diameter of ∼15 nm, an outer diameter of ∼30 nm, and an interlayer (002) d-spacing of 0.63 nm. This catalytic thermal reaction occurring at low temperatures is important for the large-scale preparation of similar transition-metal disulfide nanotubes.     

Synthesis and characterization of ferroelectric SrBi<Subscript>2</Subscript>Ta<Subscript>2</Subscript>O<Subscript>9</Subscript> nanotubes arrays

Ferroelectric SrBi₂Ta₂O₉ nanotubes were fabricated by sol–gel dipping template technique and characterized by X-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy. They had a single orthorhombic perovskite structure, and most of SBT nanotubes showed highly preferential crystal growth along the [115] orientation. FE-SEM and TEM investigations showed that nanotubes have smooth wall morphologies and well-defined diameters corresponding to the diameter of the applied template. From HRTEM results, the clear lattice fringes indicated that the nanotubes are structurally uniform and well crystallized. The growth mechanisms of SBT nanotubes into the AAO templates were explored.     

Synthesis and characterization of La<Subscript>0.8</Subscript>Sr<Subscript>0.2</Subscript>Co<Subscript>0.5</Subscript>Fe<Subscript>0.5</Subscript>O<Subscript>3±δ</Subscript> nanopowders by microwave assisted sol–gel route

Nano-crystalline La_0.8Sr_0.2Co_0.5Fe_0.5O_3±δ powder has been successfully synthesized by microwave assisted sol–gel (MWSG) method. The decomposition and crystallization behavior of the gel-precursor was studied by Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) analysis. From the result of FT-IR and X-ray diffraction patterns, it is found that a perovskite La_0.8Sr_0.2Co_0.5Fe_0.5O_3±δ was formed by irradiating the precursor at 700 W for 3 min, but the well-crystalline perovskite La_0.8Sr_0.2Co_0.5Fe_0.5O_3±δ was obtained at 700 W for 35 min. Morphological and specific area analysis of the powder were done by transmission electron microscopy (TEM), scanning electron microscope (SEM) and Brunauer–Emmett–Teller (BET). The surface areas measured was 38.9 m²/g and the grain size was ∼23 nm. Electrochemical properties of pure LSCF cathode on YSZ electrolyte at intermediate temperatures were investigated by using AC impedance analyzer, which shows a low area specific resistance (0.077 Ω cm² at 1073 K and 0.672 Ω cm² at 953 K). Moreover, the synthesis period of 20 h usually observed for conventional heating mode is reduced to a few minutes. Thus, the MWSG method is proved to be a novel, extremely facile, time-saving and energy-efficient route to synthesize LSCF powders.     

Influence of AlCl<Subscript>3</Subscript> on aggregation stability of aqueous dispersions of kraft lignin according to filtration through track membranes

The influence of AlCl₃ (0–10⁻³ M) and pH (9.5–2.0) on the aggregation of dilute (10 mg/l) aqueous dispersions of kraft lignin is studied by filtration through several track membranes with pore diameters of 50–2500 nm. AlCl₃ is shown to have markedly higher coagulating ability than NaCl and CaCl₂. In a pH range of 4.1–7.0, which corresponds to the significant hydrolysis of AlCl₃, the concentration inversion of AlCl₃ coagulating ability is observed when passing from 10⁻⁴ to 10⁻³ M, which is caused by the charge reversal of negatively charged kraft lignin particles under the action of AlCl₃ hydrolysis products.     

Facile preparation and electrochemical properties of large-scale Li<Subscript>1+<Emphasis Type="Italic">x</Emphasis></Subscript>V<Subscript>3</Subscript>O<Subscript>8</Subscript> nanobelts

Large-scale Li_1+x V₃O₈ nanobelts were successfully fabricated using filter paper as deposition substrate through a simple surface sol–gel method. The nanobelts were as long as tens of micrometers with widths of 0.4–1.0 μm and thickness of 50–100 nm. The nanobelts were characterized by X-ray diffration (XRD), Fourier infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM). The formation mechanism of the nanobelts was investigated, showing that the morphology of the nanobelts is mainly determined by the calcination temperature. Electrochemical properties of the Li_1+x V₃O₈ nanobelts were characterized by charge–discharge experiments, and the results demonstrate that the Li_1+x V₃O₈ nanobelts exhibit a high discharge capacity (278 mAh g⁻¹) and excellent cycling stability.     

Preparation of novel visible-light-driven In<Subscript>2</Subscript>O<Subscript>3</Subscript>–CaIn<Subscript>2</Subscript>O<Subscript>4</Subscript> composite photocatalyst by sol–gel method

Novel visible-light-activated In₂O₃–CaIn₂O₄ photocatalysts were developed in this paper through a sol–gel method. The photocatalytic activities of In₂O₃–CaIn₂O₄ composite photocatalysts were investigated based on the decomposition of methyl orange under visible light irradiation (λ > 400 nm). The obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrum (EDS), X-ray photoelectron spectroscopy (XPS) and UV–vis diffused reflectance spectroscopy (DRS). The results revealed that the In₂O₃–CaIn₂O₄ composite samples with different In₂O₃ and CaIn₂O₄ content can be obtained by controlling the synthesis temperature, and the composite photocatalysts extended the light absorption spectrum toward the visible region. The photocatalytic tests indicated that the composite samples demonstrated high visible-light activity for decomposition of methyl orange. The significant enhancement in the In₂O₃–CaIn₂O₄ photo-activity under visible light irradiation can be ascribed to the efficient separation of photo-generated carriers in the In₂O₃ and CaIn₂O₄ coupling semiconductors.     

Metamagnetic DyAlO<Subscript>3</Subscript> nanoparticles with very low magnetic moment

Nanocrystalline dysprosium monoaluminate (DyAlO₃) has been synthesized by modified sol–gel method after sintering the precursor gel at 950 °C. The micro-structural features have been verified by X-ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy. The XRD pattern confirms the formation of single-phase DyAlO₃; the average size of the nanoparticles is 50 nm. X-Ray photoelectron spectroscopy has been used to study the chemical composition and bonding in the samples. The binding energies of core-level electrons in Dy, Al and O in DyAlO₃ nanopowder have been found slightly shifted compared to the respective values of the same elements. Both AC and DC magnetic susceptibilities have been measured in the temperature range 2–300 K. Unusually low effective magnetic moment of Dy³⁺, μ_eff = 0.38, has been derived from the inverse magnetic susceptibility–temperature plot between 4 and 252 K. The Nèel temperature, T_N = 3.920 K and exchange interaction constant J/k = −1.74 K, have been also determined.     

Synthesis of LiNi<Subscript>1/3</Subscript>Co<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>O<Subscript>2</Subscript> nanoparticles by modified Pechini method and their enhanced rate capability

Layered LiNi_1/3Co_1/3Mn_1/3O₂ nanoparticles were prepared by modified Pechini method and used as cathode materials for Li-ion batteries. The pyrolytic behaviors of the foamed precursors were analyzed by use of simultaneous thermogravimetric and differential thermal analysis (TG-DTA). Structure, morphology and electrochemical performance characterization of the samples were investigated by X-ray diffraction (XRD), field emission scanning electron macroscopy(SEM), Brunauer-Emmett-Teller (BET) specific surface area and charge–discharge tests. The results showed that the samples prepared by modified Pechini method caclined at 900 °C for 10 h were indexed to pure LiNi_1/3Co_1/3Mn_1/3O₂ with well hexagonal structure. The particle size was in a range of 100–300 nm. The specific surface area was larger than that of the as-obtained sample by Pechini method. Initial discharge capacity of 163.8 mAh/g in the range 2.8–4.4 V (vs. Li/Li⁺) and at 0.1C for LiNi_1/3Co_1/3Mn_1/3O₂ prepared by modified Pechini method was obtained, higher than that of the sample prepared by Pechini method (143.5 mAh/g). Moreover, the comparison of electrochemical results at different current rates indicated that the sample prepared by modified Pechini method exhibited improved rate capability.     

Fabrication parameter-dependent morphologies of self-organized ZrO<Subscript>2</Subscript> nanotubes during anodization

Zirconia (ZrO₂) nanotubes have been synthesized using a facile anodizing process in organic electrolyte systems containing a low content of fluoride. The nanotube architecture evolution was recorded at different anodization periods (1–24 h) by scanning electron microscopy. A compact layer was found between the Zr substrate and its upper tubular layer after 1 h of anodization, whereas after further anodization for 3 h the compact layer disappeared. Meanwhile, ZrO₂ nanotubes turned to a uniform structure from top to bottom. However, after 18–24-h-long anodization, the uniform tubular layer was replaced by a random layer composed of various structural defects. Since the compact layer was not completely dissolved, the retained compact layer yielded O-rings with double walls on the outer surface of the nanotubes.     

Synthesis of CeVO<Subscript>4</Subscript> Crystals with Different Sizes and Shapes

Tetragonal CeVO₄ was prepared through hydrothermal treatment and sonication method with the same precursor in the absence of any catalysts or templates, and the products were characterized by XRD, TEM and Raman. It is found that microrods, nanoparticles, nanorods and nanoplates have been obtained. The bigger nanorods produced through hydrothermal treatment have average diameters of 15–25 nm and lengths of 20–60 nm. The smaller nanorods prepared through ultrasound treatment have average diameters of 6–12 nm and lengths of 10–18 nm. Uniform nanoplates have been produced. The nanoplates produced through hydrothermal method are composed of CeVO₄ and CeO₂. The mechanism of shape changing has been discussed. And the existing vanadium which is sensitive to the pH value of synthesis solution may be a key factor for the resulted sizes and shapes of the obtained nanocrystals. The samples prepared through hydrothermal treatment and sonication method were used as the catalysts for the combustion of trichloroethylene to test their catalytic activity.     

Template-based electrophoretic growth of PbZrO<Subscript>3</Subscript> nanotubes

Lead zirconate (PbZrO₃) nanotubes have been grown using porous anodic alumina templates. Sol–gel electrophoresis technique was utilized to form the nanotubes on the pore walls. The alumina templates were prepared using various anodizing voltages and times to achieve different pore diameters and lengths. Phosphoric acid solution was employed as the anodizing electrolyte. Stabilized lead zirconate sols were prepared using lead acetate trihydrate and an alkoxide precursor of zirconium. Acetic acid was used as the modifier. The prepared sols were driven into the template channels under various electrophoretic voltages and times, and the effect of the electrophoresis parameters on the formation of nanotubes was investigated. The filled templates were dried at 100 °C and sintered at 700 °C. Scanning and transmission electron microscopy (SEM and TEM) investigations demonstrated the tubular form of the lead zirconate arrays. The SEM investigations also showed the nanotubes have been efficiently grown in the template pores. The TEM studies further confirmed the polycrystalline nature of the tubes.     

Fabrication and characterization of TiO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript> composite nanoparticles and polyurethane/(TiO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript>) nanocomposite films

TiO₂–SiO₂ composite nanoparticles were prepared by a sol–gel process. To obtain the assembly of TiO₂–SiO₂ composite nanoparticles, different molar ratios of Ti/Si were investigated. Polyurethane (PU)/(TiO₂–SiO₂) hybrid films were synthesized using the “grafting from” technique by incorporation of modified TiO₂–SiO₂ composite nanoparticles building blocks into PU matrix. Firstly, 3-aminopropyltriethysilane was employed to encapsulate TiO₂–SiO₂ composite nanoparticles’ surface. Secondly, the PU shell was tethered to the TiO₂–SiO₂ core surface via surface functionalized reaction. The particle size of TiO₂–SiO₂ composite sol was performed on dynamic light scattering, and the microstructure was characterized by X-ray diffraction and Fourier transform infrared. Thermogravimetric analysis and transmission electron microscopy (TEM) employed to study the hybrid films. The average particle size of the TiO₂–SiO₂ composite particles is about 38 nm when the molar ratio of Ti/Si reaches to1:1. The TEM image indicates that TiO₂–SiO₂ composite nanoparticles are well dispersed in the PU matrix.     

Synthesis of electrospun BaSrTiO<Subscript>3</Subscript>/PVP nanofibers

Ba_1−x Sr _x TiO₃(x = 0–0.5, BST) nanofibers with diameters of 150–210 nm were prepared by using electrospun BST/polyvinylpyrrolidone (PVP) composite fibers by calcination for 2 h at temperatures in the range of 650–800 °C in air. The morphology and crystal structure of calcined BST/PVP nanofibers were characterized as functions of calcination temperature and Sr content with an aid of XRD, FT-IR, and TEM. Although several unknown XRD peaks were detected when the fibers were calcined at temperatures less than 750 °C, they disappeared with increasing the temperature (above 750 °C) due to its thermal decomposition and complete reaction in the formation of BST. In addition, the FT-IR studies of BST/PVP fibers revealed that the intensities of the O–H stretching vibration bands (at 3430 and 1425 cm⁻¹) became weaker with increasing the calcination temperature and a broad band at 540 cm⁻¹, Ti–O vibration, appeared sharper and narrower after calcination above 750 °C due to the formation of metal oxide bonds. However, no effect of Sr content on the crystal structure of the composites was detected.     

Synthesis of non-agglomerated Ba<Subscript>0.77</Subscript>Ca<Subscript>0.23</Subscript>TiO<Subscript>3</Subscript> nanopowders by a modified polymeric precursor method

In this work, we have studied the influence of the pH on the synthesis and structural properties of the Ba_0.77Ca_0.23TiO₃ nanopowders synthesized by a modified polymeric precursor method, in order to achieve non-agglomerated powders. Synthesis, morphology, thermal reactions, crystallite and average particle size of the synthesized powders were investigated through thermal analysis (DTA/TG), X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM) and Infrared spectroscopy. In summary, Ba_0.77Ca_0.23TiO₃ nanopowders were synthesized for the first time at a relative low temperature (500 °C). It was also found that the alkalinity and acidity of the solution presented a great influence on the powder properties. The best results were obtained from solutions with pH = 8.5 and 11 whose nanopowders presented weakly agglomerate, with homogeneous particle size and a narrow size distribution (30–40 nm). This behavior could be explained based on the FT-IR results in which it was possible to see the increased of the chelation in higher pHs.     

Fabrication and properties of MgF<Subscript>2</Subscript> composite film modified with carbon nanotubes

Carbon nanotubes (CNTs) were used to modify magnesium fluoride (MgF₂) film via the spin coating technique. Nanoparticles of MgF₂ were in situ synthesized on surfaces of CNTs resulted in the composites (MgF₂–CNTs) by means of sol–gel technique. The sizes of the MgF₂ nanoparticles in situ synthesized on CNTs surfaces could be modulated by processing the MgF₂ sol–gel in different ways. The MgF₂–CNTs as prepared was mixed with MgF₂ sol to fabricate composite films (MgF₂–CNTs/MgF₂). Instead of adding directly CNTs, adding MgF₂–CNTs, into MgF₂ sol could effectively improve the dispersion of CNTs, avoid emergence of carbon clusters in the compsite film, decrease surface roughness of the film, and enhance the interaction between the CNTs and MgF₂ matrix. In the paper, the MgF₂ nanoparticles were in situ synthesized on the surfaces of multi-walled carbon nanotubes (MWCNTs) and single-walled carbon nanotubes (SWCNTs) respectively to prepare MgF₂–SWCNTs/MgF₂ and MgF₂–MWCNTs/MgF₂ composite films. Experimental results showed that the transparency of the MgF₂–SWCNTs/MgF₂ composite film was higher than that of the MgF₂–MWCNTs/MgF₂ film in the range of ultraviolet, visible and near-infrared wavelengths. The results showed SWCNTS could be an ideal reinforcement of MgF₂ films to get good toughness, and retain its optical transmittance at the same time.     

Characterization of NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles synthesized by various methods

Microwave-induced combustion with glycine, CTAB-assisted hydrothermal process with NaOH and NH3, EDTA assisted-hydrothermal methods have been applied to prepare NiFe₂O₄ nanoparticles for the first time. Structural and magnetic properties of the products were investigated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmison electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and electron spin resonance spectrometry (EPR). TEM measurements showed that morphology of the product depends on the synthesis method employed. The average cystallite size of NiFe₂O₄ nanoparticles was in the range of 14–59 nm as measured by XRD. The uncoated sample (Method A) had an EPR linewidth of 1973 Oe, the coated samples reached lower values. The magnetic dipolar interactions existing among the Ni ferrite nanoparticles are reduced by the coatings, which could cause the decrease in the linewidth of the EPR signals. Additionally, the linewidth increases with an increase in the size and the size distribution of nanoparticles.     

Steric distortion of planar NiP<Subscript>2</Subscript>N<Subscript>2</Subscript> chromophores: a spectral,cyclic voltammetric and single crystal X-ray structural study

The complexes trans-[Ni(4-MP)₂(NCS)₂]·MeCN (1) and trans-[Ni(3-MP)₂(NCS)₂] (2) (4-MP = tri(4-methylphenyl)phosphine, 3-MP = tri(3-methylphenyl)phosphine) were prepared and characterized by IR, UV–visible, NMR spectra, CV, TGA and single crystal X-ray crystallography. Both the complexes have planar geometry and are diamagnetic. The Ni–P distances in both complexes are relatively short as a result of strong back donation from nickel to phosphorus. The phenyl rings in the 3-MP analogue (2) show increased pitching with reference to the plane formed by the ipso carbons due to increased steric effects. For complex (2), the N–Ni–N and P–Ni–P angles are significantly lower than the almost linear N–Ni–N and N–Ni–P angles observed for both complex (1) and trans-[Ni(PPh₃)₂(NCS)₂]. This observation indicates that the 3-methylphosphine ligand forces complex (2) to distort towards a tetrahedral geometry. IR spectra of both complexes show strong bands around 2,090 cm⁻¹ due to N-coordinated thiocyanate, while the electronic spectra contain d–d transitions around 452 nm. Cyclic voltammograms show that the irreversible one-electron reduction potentials increase in the following order: trans- [Ni(PPh₃)₂(NCS)₂] < trans- [Ni(3-MP)₂(NCS)₂] < trans-[Ni(4-MP)₂(NCS)₂], revealing the electron releasing effect of the methyl groups. The planar complexes exhibit interallogony in coordinating solvents.     

DSC investigation of nanocrystalline TiO<Subscript>2</Subscript> powder

The aim of the article is to investigate the influence of particle size on titanium dioxide phase transformations. Nanocrystalline titanium dioxide powder was obtained through a hydrothermal procedure in an aqueous media at high pressure (in the range 25–100 atm) and low temperature (≤200 °C). The as-prepared samples were characterized with respect to their composition by ICP (inductive coupled plasma), structure and morphology by XRD (X-ray diffraction), and TEM (transmission electron microscopy), thermal behavior by TG (thermogravimetry) coupled with DSC (differential scanning calorimetry). Thermal behavior of nanostructured TiO₂ was compared with three commercial TiO₂ samples. The sequence of brookite–anatase–rutile phase transformation in TiO₂ samples was investigated. The heat capacity of anatase and rutile in a large temperature range are reported.     

Preparation of highly active photocatalyst anatase TiO<Subscript>2</Subscript> by mixed template method

TiO₂ nanocrystals with diameters 8–10 nm have been prepared through sol–gel method using a mixed template of polyethylene glycol (PEG) and cetytrimethylammonium bromide (CTAB) at low temperature. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution (HR) TEM and fourier transform infrared spectroscopy (FT-IR) etc. XRD analysis showed the TiO₂ photocatalysts prepared with mixed template are pure anatase. FTIR spectrum revealed that the cationic surfactant provides CTA⁺ molecules and bonds to Ti–O to prevent the condensation reaction. PEG plays a dispersant role in controlling the structure of nano-TiO₂ particles. CTAB and PEG incorporated with each other to restrain the growth of crystal nucleus and control the size of grain. The self-assembling process has been confirmed by HRTEM. PEG played different role in mixed template from the single template. The photocatalytic activity of samples was determined by using as a model reaction. The results showed that TiO₂ photocatalysts with mixed template have higher photocatalytic activity than P25.     

Some studies on the phase formation and kinetics in TiO<Subscript>2</Subscript> containing lithium aluminum silicate glasses nucleated by P<Subscript>2</Subscript>O<Subscript>5</Subscript>

Lithium aluminum silicate (LAS) glasses of compositions (wt%) 10.6Li₂O–71.7SiO₂–7.1Al₂O₃–4.9K₂O–3.2B₂O₃–1.25P₂O₅–1.25TiO₂ were prepared by the melt quench technique. Crystallization kinetics was investigated by the method of Kissinger and Augis–Bennett using differential thermal analysis (DTA). Based on the DTA data, glass ceramics were prepared by single-, two-, and three-step heat treatment schedules. The interdependence of different phases formed, microstructure, thermal expansion coefficient (TEC) and microhardness (MH) was investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), thermo-mechanical analysis (TMA), and microhardness (MH) measurements. Crystallization kinetics revealed that Li₂SiO₃ is the kinetically favored phase with activation energy of 91.10 kJ/mol. An Avrami exponent of n = 3.33 indicated the dominance of bulk crystallization. Based upon the formation of phases, it was observed that the two-stage heat treatment results in highest TEC glass ceramics. The single-step heat treatment yielded glass ceramics with the highest MH.