Template growth of vertically aligned carbon nanotubes using self-assembled monolayers of SiO2 particles by Langmuir–Blodgett technique

The thermal stability of nanocrystalline 3R-CuCrO₂ obtaining by hydrothermal method was investigated by annealing treatment, XRD, FT-IR, XPS and TG. The three temperature domains corresponding to thermal stability of 3R-CuCrO₂ nanocrystals (25–400 °C), destabilization of nanocrystalline 3R-CuCrO₂ phase (400–800 °C) and recrystallization of 3R-CuCrO₂ in microcrystalline state over 800 °C, were determined by the specific hydrothermal synthesis conditions. This study has indicated that nanocrystals with delafossite structure synthesized by hydrothermal method exhibit nanocrystalline state up to a reasonably high temperature, about 390 °C, which could be interesting for technical applications and the classical theory of the grain growth.     

Synthesis,photophysical properties,and photocatalytic applications of Bi doped NaTaO3 and Bi doped Na2Ta2O6 nanoparticles

Phase formation and photophysical properties of bismuth doped sodium tantalum oxide (perovskite, defect pyrochlore) nanoparticles prepared by a hydrothermal method were studied in detail. It was revealed that the synthesis conditions like NaOH concentration and bismuth precursor (NaBiO₃·2H₂O) markedly affect the crystal structure of sodium tantalum oxide. At low NaOH concentration and high bismuth precursor (NaBiO₃·2H₂O) content, Bi doped Na₂Ta₂O₆ (defect pyrochlore) phase was predominantly formed, while at higher NaOH concentration, Bi doped NaTaO₃ (perovskite) phase was formed. It was observed that the defect pyrochlore (Bi doped Na₂Ta₂O₆) phase was formed and stabilized by the presence of dopant precursor (NaBiO₃·2H₂O). The chemical analysis of the samples confirmed the doping of Bi³⁺ cations in both phases. Doping of bismuth enabled visible light absorption up to 500 nm in perovskite and defect pyrochlore type sodium tantalum oxide. Bi doped NaTaO₃ samples showed better performance for the photocatalytic degradation of rhodamine B than that of Bi doped Na₂Ta₂O₆, under visible light irritation (λ>420 nm). The present results shed light on phase formation of sodium tantalate and these results are useful in understanding properties of NaTaO₃ based compounds, synthesized by the hydrothermal method.     

Preparation, characterization and room temperature photoluminescence properties of a zinc oxide nanosheet network grown on glass substrate by a facile chemical route

An ultralong and ultrathin zinc oxide nanosheet network grown on glass substrate is prepared using an organic CTAB (cetyltrimethylammonium bromide, CH₃(CH₂)₁₅N⁺(CH₃)₃Br⁻) and the simple chemical materials (Zn(AC)₂·2H₂O and NaOH) by hydrothermal method. The morphology and microstructure of ZnO nanosheet network have been characterized by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and UV–vis spectroscopy. The results revealed that the product grown on glass substrate was the ultralong and ultrathin zinc oxide nanosheet network and the crystalline hexagonal wurtzite ZnO crystal structure. The zinc oxide nanosheet network exhibits room temperature photoluminescence (RTPL) characteristics and three blue emissions located at 452, 459, and 469 nm, and a green emission located at about 494 nm were observed.     

The interaction of H2O molecules with iron films studied with MIES,UPS and XPS

X-Ray Photoelectron Spectroscopy (XPS), Metastable Induced Electron Spectroscopy (MIES) and Ultraviolet Photoelectron Spectroscopy (UPS) were applied to study the interaction of H₂O molecules with iron films.During the interaction with H₂O molecules under ultrahigh vacuum conditions, an oxide film is formed on the iron surface. UPS and XPS still show metallic contributions, even for a surface which is exposed to about 10³ L. The oxide film thickness amounts to about 1.8 nm. No hydroxide formation is observed at all, neither in UPS nor in MIES. Further impinging H₂O molecules do not interact with the surface, because the oxide film inhibits the dissociation of impinging molecules.H₂O exposure beyond 10⁹ L does not lead to a significant increase of the oxide layer, which saturates at a thickness of 1.8 nm. In particular, no surface hydroxide is observed at this exposure. Neither XPS UPS nor MIES reveal any indication for this.     

Combustion synthesis of nickel ferrite powders: Effect of NaClO4 content on their characteristics and magnetic properties

Magnetic powders of nickel ferrite (NiFe₂O₄) were successfully synthesized by combustion synthesis in air using iron (Fe), iron oxide (Fe₂O₃), and nickel oxide (NiO) as reactants and sodium perchlorate (NaClO₄) as fuel (or oxidizing agent). The thermal behaviors were characterized using thermogravimetric analysis (TG) and differential thermal analysis (DSC). The as-combusted and final nickel ferrite powders were characterized in terms of chemical composition and morphology by X-Ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM) coupled with energy dispersive X-Ray spectroscopy (EDX). In addition, magnetic properties were examined by vibrating sample magnetometer (VSM). The results of TG/DSC analysis indicated that increasing the content of NaClO₄ increased the exothermicity of combustion reaction. XRD indicated that the final nickel ferrite powders formed a single spinel NiFe₂O₄ phase when the amount of NaClO₄ used was 0.08 or 0.10 mol. SEM revealed roughly octahedron particles with sizes in a sub-micrometer range (∼500 nm). All final products exhibited soft magnetism and, synthesis that included 0.1 mol of NaClO₄ produced pure NiFe₂O₄ powders that had a saturation magnetization (M_s) of 58.93 emu/g, which is higher than the reported value (55 emu/g) for the bulk product.     

Sulfur-catalyzed phase transition in MoS2 under high pressure and temperature

We report phase transition and stability of MoS₂ with and without the presence of sulfur melt under high-pressure and high-temperature conditions. Rhombohedral (3R) phase is found to be a high-temperature phase of MoS₂ at high pressures. Excess sulfur melt catalyzes the hexagonal (2H) to rhombohedral (3R) phase transformation and lowers the conversion temperature by more than 280 K. Boundary between 2H and 3R phases has been delineated with a negative slope. Based on experimental observations, sulfur-catalyzed 2H→3R transformation mechanisms are proposed involving atomic exchange between MoS₂ and sulfur, which is different from the case of without excess sulfur that proceeds through rotation and translation of the S–Mo–S sandwich layers.     

Structural and magnetic properties of reduced graphene oxide-TiO2 nanoflower composite

We have focused on the structural and magnetic properties of hazardous acid free synthesis of anatase titanium dioxide (TiO₂) phase nanoflower and reduced graphene oxide-TiO₂ (rGO-TiO₂) nanocomposite using hydrothermal process. Because, strong acids free synthesis is environmental friendly and reduce overall cost of synthesized samples. In the synthesis of rGO-TiO₂, synthesized TiO₂ nanoflower and graphene oxide (GO) were used as reagents. The resulting materials have analyzed using different techniques such as, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and Fourier Transformation Infrared spectrophotometer for confirmation of flower like morphology, crystalline phase and chemical composition. Moreover, VSM analysis has revealed the ferromagnetism induced in the rGO-TiO₂ composite at room temperature. The values of saturation magnetization were found to be 0.002 and ~ 0.243±0.04 emu/g for TiO₂ nanoflower and rGO-TiO₂ nanocomposite, respectively. In comparison of pure TiO₂, rGO-TiO₂ exhibited larger magnetization at room temperature. This is because presences of various edge and site defects such as topological and point defects like vacancies, which create localized unpaired spins in reduced graphene oxide (rGO), induce the ferromagnetism behavior in rGO-TiO₂ nanocomposite.     

三方和四方相PbZr0.5Ti0.5O3 的结构稳定性和电子结构的第一性原理研究

采用基于密度泛函理论的第一性原理超原胞方法和虚晶近似方法, 在局域密度近似和广义梯度近似下系统研究了三方相和四方相 PbZr_0.5Ti_0.5O₃的能量稳定性、原子结构以及电子结构. 计算结果表明三方相的能量比四方相低, 说明三方相结构更加稳定, 并且发现利用广义梯度近似计算的结构参数与实验值符合得更好. 电子结构表明, 两种相的Ti/Zr的3d电子和O的2p电子间存在明显的轨道杂化, 并且Ti-O之间的作用比Zr-O作用更强;Pb的6s和5d电子与O的2s和2p电子也分别存在轨道杂化. 而三方相中Pb的5d电子与O的2s电子杂化比四方相更强, 进一步说明三方相比四方相结构更加稳定.     

Hydrothermal synthesis of spinel Li1+x Mn2O4 as cathode material for rechargeable lithium battery

Abstract

The hydrothermal synthesis of Li-Mn spinel oxide (Li_1+xMn₂O₄) was undertaken in order to develop high quality, low cost cathode material for a rechargeable lithium battery. In our experiments, γ-MnOOH, LiOH · H₂O and H₂O₂ were used as starting materials to synthesize Li-Mn spinel oxide under hydrothermal conditions of 180-230°C and about 1.0-2.8 MPa. The chemical composition and particle size of the Li_1+xMn₂O₄ is easily controlled in the hydrothermal reaction. The Li_1+xMn₂O₄ produced was characterized by X-ray diffraction, with the spinel phase having a Li/Mn ratio of 0.50-0.60. There is convincing evidence, as a result of this work, that our synthesis process is most suitable for producing high quality cathode material that can be used in a rechargeable lithium battery.     

Direct synthesis of AgInO2

Potential applications as transparent conducting oxides have made the study of ternary metal oxides based on the delafossite structure very attractive. The well known and understood thermal instability of noble metal oxides, and therefore the associated problems with high-temperature solid-state techniques to yield pure complex oxides based on noble metals, clearly illustrates the need for low-temperature alternatives. For the first time, synthesis of 3R-AgInO₂ at low temperature (175 °C) and pressure (<10 atm) was achieved by a single-step hydrothermal technique. Particle size of the orange crystallites ranged from 3 to 7 μm.     

An XPS,ISS and ESR Comparative Study of Eight-Coordination of Copper (II) Ions in the CuTho Compounds

In this study, we attempted to clarify the coordination state and the distribution of copper (II) ions in the CuThO compounds prepared by coprecipitation, by using several physico-chemical techniques in particular, X-Ray Photoelectron Spectroscopy (XPS).

For atomic ratios Cu/Th ≤ 0.25, the copper (II) species are mainly located near the thoria surface. The Cu2p_3/2 level shows a chemical shift towards the lower binding energy compared to Cu²⁺ ions in CuO and also a net decrease in the intensity of the satellite peak, characteristic of copper (11). A relation between these observations and the covalent character o f Cuzt- 02- bond i s esta- blished. Eightfold coordination of copper (11) i n the thoria lattice i s evident. These conclusions are in good agreement with Electron Spin Resonance (ESR) results.

For a higher atomic ratio (Cu/Th > 0.25), a formation o f copper oxide crystallites i s observed on the thoria surface.     

Oleylamine‐Assisted Phase‐Selective Synthesis of Cu2−xS Nanocrystals and the Mechanism of Phase Control

Environmentally friendly Cu_2?x S compounds exist in many different mixed phases in nature, while their nanoscale counterparts can be pure phase with interesting localized surface plasmon resonance properties. Because of the complexity of composition and phase, controllable synthesis of Cu_2?x S nanocrystals becomes an important scientific issue in colloidal chemistry. In this work, a hot‐injection method is developed to synthesize Cu_2?x S nanocrystals by injecting a sulfur precursor into a copper precursor using oleylamine and octadecene as solvents. By varying the reaction parameters (temperature, volume ratio of oleylamine/octadecene, molar ratio of Cu/S in the precursors), hexagonal CuS, monoclinic Cu_1.75S, and rhombohedral Cu_1.8S, nanocrystals can be selectively synthesized, providing a platform to illustrate the mechanism of crystal phase control. The crystal phase control of Cu_2?x S nanocrystals is oleylamine‐determined by controlling the molar ratio of Cu/S in the reaction precursors as well as the ratio of Cu_2?x S clusters/Cu⁺ in the subsequent reaction. More importantly, temperature plays an important role in varying the molar ratio of Cu/S and Cu_2?x S clusters/Cu⁺ in the reaction system, which significantly influences the crystal phase of the resulting Cu_2?x S nanocrystals. The understanding into crystal control provides a guideline to realize reproducible phase‐selective synthesis and obtain well‐defined high‐quality materials with precise control.     

Electronic topological transition and phase transition in rhodium and iridium based inter metallic compounds

Of the Rh₃Y, Rh₃La, Ir₃Y and Ir₃La inter-metallic compounds, the compound Rh₃Y exists in hexagonal structure, Ir₃Y and Ir₃La exist in rhombohedral structure, whereas the compound Rh₃La exists in both hexagonal and rhombohedral structures. Based on our tight binding-linear muffin tin orbital (TB-LMTO) study of other rhodium and iridium-based Rh₃X and Ir₃X (where X=Ti, Zr, Hf, V, Nb, Ta and Sc) inter-metallic compounds of AuCu₃ type cubic structure, an attempt is made to examine whether the compounds Rh₃Y, Rh₃La, Ir₃Y and Ir₃La will undergo a structural phase transition to cubic structure from their experimentally reported structures. From our study, it is observed that the compounds Rh₃Y and Rh₃La undergo a structural phase transition to cubic phase at 4.5 and 10.1 GPa, respectively, from their experimentally reported hexagonal and rhombohedral phases. Further it is predicted that both the compounds Ir₃Y and Ir₃La can exist in the cubic phase itself at ambient condition, in contrary to the experimental observation. From the band structure outputs that have been plotted for the compounds under compression, it is observed that the compounds Rh₃La, Ir₃Y and Ir₃La undergo the Lifshitz type of transition which may change the Fermi surface topology and hence the physical properties of these compounds.     

Synthesis and characterization of nitrogen-doped TiO2 coatings on reduced graphene oxide for enhancing the visible light photocatalytic activity

Nitrogen-doped TiO₂ coatings on reduced graphene oxide were prepared via a sonochemical synthesis and hydrothermal process. The nanocomposites showed improved photocatalytic activity due to their large specific surface areas (185–447 m²/g), the presence of TiO₂ in the anatase phase, and a quenched photoluminescence peak. In particular, GN3-TiO₂ (nitrogen-doped TiO₂ coatings on rGO with 3 ml of titanium (IV) isopropoxide) exhibited the best photocatalytic efficiency and degradation rate among the materials prepared. With nitrogen-doped on the reduced graphene oxide surface, the photocatalytic activity is enhanced approximately 17.8 times compared to that of the pristine TiO₂. The dramatic enhancement of activity is attributed to the nitrogen contents and rGO effectively promoting charge-separation efficiency and providing abundant catalytically active sites to enhance the reactivity. The composites also showed improved pollutant adsorption capacity, electron–hole pair lifetime, light absorption capability, and absorbance of visible light.     

Template-free hydrothermal synthesis of ZnO microrods for gas sensor application

Zinc oxide microrods with controlled diameter were prepared without the addition of template and additive by a simple hydrothermal route only using Zn(CH₃COO)₂·2H₂O as a precursor. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and electron diffraction (ED). The crystal structure of prepared ZnO microrods is hexagonal phase polycrystalline with zincite structure. With the increase of the precursor concentration from 0.05 M to 0.6 M, the diameter of the ZnO microrods increased from 1 μm to 5 μm. A localized oriented attachment mechanism was prepared to account for the formation of ZnO microrods. The gas-sensing performance experiments indicated that the prepared ZnO microrods exhibited highly sensitive, selective gas-sensing properties, and good stability to acetone vapor. The response and recovery time of ZnO-based gas sensor to 100 ppm acetone vapor are 12 s and 18 s, respectively. The mechanism of the ZnO-based sensor was investigated.     

Compression behavior of the delafossite-type metallic oxide PdCoO2 below 10 GPa

The compression behavior of delafossite-type metallic oxide PdCoO₂ below 10 GPa has been investigated by in situ high pressure X-ray diffraction measurement using synchrotron radiation. It is found that the delafossite-type structure of PdCoO₂ is stable below 10 GPa. It should be noted that compression behavior of PdCoO₂ is anisotropic. Pressure dependence of the lattice parameters indicates that the a-axis is more compressible than the c-axis. The lattice parameter ratio c/a in the hexagonal unit increases with increasing pressure. The calculated zero-pressure bulk modulus is 224 GPa. It is found that the above characteristic compression behaviors of PdCoO₂ are the same as those of the delafossite CuFeO₂. The compressibilities of the a-axis of both PdCoO₂ and CuFeO₂ are highly different although those of the c-axis are almost the same.     

Rectifying resistance switching behaviors of SnO2 microsphere films modulated by top electrodes

Based on the bipolar resistive switching (RS) characteristics of SnO₂ films, we have fabricated a new prototypical device with sandwiched structure of Metal/SnO₂/fluorine-doped tin oxide (FTO). The SnO₂ microspheres film was grown on FTO glass by template-free hydrothermal synthesis, which was evaporated with various commonly used electrodes such as aluminium (Al), silver (Ag), and gold (Au), respectively. Typical self-rectifying resistance switching behaviors were observed for the RS devices with Al and Au electrodes. However, no obvious rectifying resistance switching behavior was observed for the RS device with Ag electrode. Above results were interpreted by considering the different interface barriers between SnO₂ and top metal electrodes. Our current studies pave the ways for modulating the self-rectifying resistance switching properties of resistive memory devices by choosing suitable metal electrodes.     

Optical properties of p-type CuAlO2 thin film grown by rf magnetron sputtering

We report the structural and optical properties of copper aluminium oxide (CuAlO₂) thin films, which were prepared on c-plane sapphire substrates by the radio frequency magnetron sputtering method. X-ray photoelectron spectroscopy (XPS) along with X-ray diffraction (XRD) analysis confirms that the films consist of delafossite CuAlO₂ phase only. The optical absorption studies show the indirect and direct bandgap is 1.8 eV and 3.45 eV, respectively. Room temperature photoluminescence (PL) measurements show three emission peaks at 360 nm (3.45 eV), 470 nm (2.63 eV) and 590 nm (2.1 eV). The first one is near band edge emission while the other two are originated from defects.     

Ultrasonication assisted and surfactant mediated synergistic approach for synthesis of calcium sulfate nano-dendrites

Calcium sulfate (CaSO₄) nano-dendrimers were fabricated successfully via ultrasonic irradiation method using calcium chloride [CaCl₂] and ammonium per sulfate [(NH₄)₂SO₄] as precursors in aqueous solution by using cetyl trimethyl ammonium bromide (CTAB) as chemical surfactants. Diffusion-induced branching growth mechanism (DIBGM), influenced with the action of head-group and hydrocarbon chain effect of cationic surfactants, was the backbone in the formation of CaSO₄ nano-dendrites. Fourier Transform Infra-red Spectroscopy (FTIR), X-Ray powder Diffraction (XRD), Atomic Emission Spectroscopy (AES), Selected Area Electron Diffraction (SAED), Field-Emission Scanning Electron Microscopy (FE-SEM), Energy-Dispersive Spectroscopy (EDS), Dynamic Light Spectroscopy (DLS) and BET surface area analyzer were used to characterize the products. Results obtained were compared with conventional stirring method that proved the superiority of sonication method to obtain well-crystalline nanostructures. Also, surfactant concentration, sonication frequency and time were noticed as the critical factors to generate such absolute morphologies at nano-crystalline size.     

Organic-ligand-assisted supercritical hydrothermal synthesis of titanium oxide nanocrystals leading to perfectly dispersed titanium oxide nanoparticle in organic phase

Titanium oxide (TiO₂) nanocyrstals which are perfectly dispersed in organic solvents are synthesized by organic-ligand-assisted supercritical hydrothermal synthesis. The addition of hexaldehyde to the supercritical hydrothermal synthesis of TiO₂ leads to the in-situ surface modification, which enables the synthsized TiO₂ nanocrystals to be perfectly dispersed in iso-octane because of its hydrophobic nature. Further, the one-pot synthesis of hybrid materials results in the significant reduction of the particles size, probably due to the capping effect of hexaldehyde to suppress the particles growth.