Morphology-controlled synthesis and growth mechanisms of branched α-MnO2 nanorods via facile microwave-assisted hydrothermal method

Multiple branched manganese oxide nanorods were obtained through the rapid one-step microwave-assisted hydrothermal synthesis by the reduction of potassium permanganate in hydrochloric acid solution without using any catalysts or surfactants. The formation mechanism of the branched α-MnO₂ was studied by systematically varying the reaction time, which were “oriented attachment” and rolling-cum-phase process. The electrochemical performance of the samples was examined by cyclic voltammetry. The specific surface area of the branched α-MnO₂ and the electrolyte in the solution were found to remarkably affect the specific capacitance. This microwave-assisted technique enables the quick and simple preparation of branched MnO₂ nanorods under mild conditions and maybe readily extended to the preparation of many other branched nanoparticles.     

Facile hydrothermal route to the controlled synthesis of α-Fe2O3 1-D nanostructures

Single-crystalline α-Fe₂O₃ 1-D nanostructures can be obtained via a facile one-step hydrothermal synthetic route. It was found that the introduction of SnCl₄ played a key role in determining the composition and morphology of α-Fe₂O₃. The addition of SnCl₄ favours the formation of Fe₂O₃ rather than FeOOH, and the morphology can be tuned from nanorod to double-shuttle as the increase of SnCl₄ concentration. The products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and selected-area electron diffraction (SAED). This simple method does not need any seed, catalyst, or template, thus is promising for large-scale and low-cost production.     

Rapid hydrothermal synthesis of SrMo1−xWxO4 powders: Structure and luminescence characterization

Strontium molybdate, strontium tungstate particles and their solid solutions (SrMo_1?xW_xO₄) with 0 ? x ? 1.0, were synthesised by means of a hydrothermal process. Crystallisation of SrMo_1?xW_xO₄ particles took place rapidly using SrSO₄ as the Sr precursor under hydrothermal conditions involving stirring (130 rpm) at 150 or 200 °C for 2 h. Structural analyses of the powders were conducted by XRD with Rietveld refinement and FT-Raman spectroscopy, and the particle shape was observed by FE-SEM. Lattice parameter measurements indicated a linear dependence of both “a₀” and “c₀” in the scheelite structured SrMo_1?xW_xO₄ with a changing W content following Vegard’s law. These analyses also provided evidence of the structural variation localised in the tetrahedral site as a result of the simultaneous incorporation of MoO₄ and WO₄ in the solid solutions formed in the compositional range of 9 ? x ? 60 mol%. The SrMo_1?xW_xO₄ particles exhibited a predominantly euhedral shuttle-shaped morphology and particle sizes varying between 0.75 and 1.5 μm. The particle growth was affected by increasing the reaction temperature and the tungsten concentration. Photoluminescence analysis (PL) revealed a marked attenuation of the blue and green emissions preferentially for the powder containing 48.5 mol% of W, which makes it potentially useful for optoelectronic applications.     

Facile synthesis of uniform ZnxCd1−xS alloyed hollow nanospheres for improved photocatalytic activities

In this work, we demonstrate that a facile template-free method has been developed for the fabrication of uniform Zn_xCd_1?xS (0 ≤ x ≤ 1) alloyed hollow nanospheres. The as-prepared Zn_xCd_1?xS hollow nanospheres have been investigated by X-ray powder diffraction, field-emission scanning electron microscopy (JEOL-6700F) and transmission electron microscopy (JEOL 3010), respectively. The research results indicate that the as-prepared Zn_xCd_1?xS hollow nanospheres are with an average diameter of 80 and 30 nm in shell thickness. As expected, the as-prepared Zn_0.5Cd_0.5S alloyed hollow nanospheres show improved photocatalytic performance towards photodegradation of Rhodamine B. These findings may open new opportunities for the design of effective, stable, and easy-recyclable photocatalytic materials.     

Clean synthesis of biocarbon-supported Ni@Pd core–shell particles via hydrothermal method for direct ethanol fuel cell anode application

Clean Technologies and Environmental Policy - Direct ethanol fuel cells (DEFCs) are devices for clean and sustainable energy production, where the generation of electrical energy occurs as a result...     

Controllable synthesis of α- and β-MnO(2): cationic effect on hydrothermal crystallization

α-?and β-MnO(2) were controllably synthesized by hydrothermally treating amorphous MnO(2) obtained via a reaction between Mn(2+) and MnO(4)(-), and cationic effects on the hydrothermal crystallization of MnO(2) were investigated systematically. The crystallization is believed to proceed by a dissolution-recrystallization mechanism; i.e.?amorphous MnO(2) dissolves first under hydrothermal conditions, then condenses to recrystallize, and the polymorphs formed are significantly affected by added cations such as K(+), NH(4)(+) and H(+) in the hydrothermal systems. The experimental results showed that K(+)/NH(4)(+) were in competition with H(+) to form polymorphs of α-?and β-MnO(2), i.e., higher relative K(+)/NH(4)(+) concentration favoured α-MnO(2), while higher relative H(+) concentration favoured β-MnO(2).     

Structure and phase transition of BiFeO3 particles prepared by hydrothermal method and the verification of crystallization–dissolution–crystallization mechanism

The optimal synthesis temperature of BiFeO₃ is found. The cube BiFeO₃ powders have a hexagonal perovskite structure with a space group R3c, while the sphere-like BiFeO₃ powders have a rhombohedral structure with a space group R3m. The growth mechanism of crystallization–dissolution–crystallization has been summarized and verified. The effect of the reaction time on the particle size in hydrothermal synthetic experiment is studied. The magnetic properties of samples prepared under different alkali concentration have been measured by vibrating sample magnetometer. It is indicated that the samples with different morphologies exhibit different magnetic properties. A reasonable explanation for this phenomenon has been given in this paper.     

Direct formation of new,phase-stable,and photoactive anatase-type Ti1−2XNbXScXO2 solid solution nanoparticles by hydrothermal method

A new anatase phase of photoactive Ti_1?2XNb_XSc_XO₂ (X = 0–0.2) solid solutions was directly formed as nanoparticles from precursor solutions of TiOSO₄, NbCl₅, and Sc(NO₃)₃ under mild hydrothermal conditions at 180 °C for 5 h using the hydrolysis of urea. With the increase of the content of niobium and scandium from X = 0 to 0.2, the lattice parameters a₀ and c₀, the crystallite size, and the optical band gap of anatase gradually increased. Their photocatalytic activity and adsorptivity were evaluated separately by the measurement of the concentration of methylene blue (MB) remained in the solution in the dark or under UV-light irradiation. The anatase-type Ti_1?2XNb_XSc_XO₂ (X = 0.05) showed approximately two times and three times as high photocatalytic activity as those of the hydrothermal anatase-type pure TiO₂ and commercially available reference pure TiO₂ (ST-01), respectively. The anatase phase of Ti_1?2XNb_XSc_XO₂ (X = 0–0.2) existed stably up to 900 °C during heat treatment in air. New rutile-type Ti_1?2XNb_XSc_XO₂ solid solutions are formed through the phase transformation. The starting temperature of anatase-to-rutile phase transformation for Ti_1?2XNb_XSc_XO₂ (X = 0–0.2) solid solutions was delayed but its completing temperature was accelerated.     

Preparation of AgIn1−xGaxSe2 films from sol–gel derived precursors via a coating method

AgIn_1?xGa_xSe₂ films were prepared via coating the pastes that contained sol–gel derived precursors and selenium powders, followed by the normal heating process without using H₂Se. Pure-phased AgIn_1?xGa_xSe₂ films were successfully obtained after heating in a reducing atmosphere (H₂/N₂) at 500 °C for 0.5 h. As the flow rate of the carrier gas was reduced, In₂O₃ and Ag₂Se phases in the obtained films disappeared owing to prolonged residence time for selenium vapor to react with the precursors. In the paste-coating process, the gallium-ion content of the prepared films was effectively adjusted using the sol–gel route. The lattice constants of AgIn_1?xGa_xSe₂ decreased with increasing the gallium-ion contents. The uniformity throughout AgIn_1?xGa_xSe₂ films was confirmed by using the grazing incident X-ray diffraction analysis. The band gap energy increased nonlinearly from 1.27 to 1.63 eV as the molar ratio of gallium ions to IIIA ions (indium ions and gallium ions) increased from 0.2 to 0.8.     

Low-temperature hydrothermal synthesis of α-MnO2 three-dimensional nanostructures

Single-crystalline α-MnO₂ three-dimensional nanostructures were synthesized via a novel redox reaction of KMnO₄ and Cr(NO₃)₃ under hydrothermal conditions. The products were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive spectroscopy (EDS), and high-resolution transmission electron microscopy (HRTEM). The addition of HNO₃ into the reaction has a significant effect on the morphologies of the final products. The α-MnO₂ three-dimensional nanostructures were obtained under the acidic condition, while α-MnO₂ nanowires were obtained without the addition of HNO₃. A mechanism for the growth of α-MnO₂ three-dimensional nanostructures was proposed.     

Synthesis of Mg1−xCoxAl2O4 blue pigments via combustion route

MgAl₂O₄ was successfully used as crystalline host network for the synthesis of cobalt-based blue ceramic pigments. Different compositions of Mg_1?xCo_xAl₂O₄ (x = 0.1–0.3) powders have been prepared by the combustion reaction of corresponding metal nitrates with mixtures of urea and β-alanine. The resultant powders were characterized by means of XRD, TG-DTA, EDAX, SEM, BET surface area, diffuse reflectance spectrometry and CIEL1a1b1 color measurement. For x = 0.2, thermal analysis investigations evidenced that combustion reaction occurs at 276 °C. XRD analysis certified the formation of the designed solid solution, no additional thermal treatment being required. EDAX elemental analysis confirmed the purity of the as-prepared compound. The resulted powders had large surface areas, which varied from 8.7 to 62.6 m²/g. The crystallite size of Mg_1?xCo_xAl₂O₄ powders was less than 15 nm. Experimental results evidenced that as the proportion of Co²⁺ increased, the crystallite size decreased and the specific surface area increased. The diffuse reflectance spectra of the Mg_1?xCo_xAl₂O₄ pigments confirmed the presence of tetrahedrally coordinated Co²⁺. CIEL1a1b1 chromatic coordinates indicated that the bluest color was obtained for x = 0.2.     

A parametric study of visible-light sensitive TiO2 photocatalysts synthesis via a facile sol–gel N-doping method

In the present work, a parametric study of visible-light sensitive TiO₂ via a facile sol–gel N-doping method was carried out. Visible-light activity of as-prepared products was assessed using solutions of methylene blue as model pollutants. Optimal visible-light activity was achieved at equal N-to-Ti precursor molar ratio and 350 °C calcinations. Characterisation of structural, chemical and optical properties of synthesised TiO₂ photocatalysts was also undertaken to elucidate the effects of N-to-Ti precursor molar ratio and calcinations temperature on the resulting photocatalytic activity. The pH value of N-doped TiO₂ sol during the preparation was also found to be an effective indicator of N-doping quality without using any post-synthesis analysis. These findings could be utilised in the successful development of TiO₂ photocatalysts or their nanocomposites for cost effective solar irradiation-driven environmental technology.     

Synthesis of acicular α-Bi2O3 microcrystals by microwave-assisted hydrothermal method

ABSTRACT

Materials based on bismuth(III) oxide are candidate to be used in optical and electronic devices because of their properties such as a variable band gap, photoconductivity, photoluminescence, high refractive index, and dielectric permittivity. These properties are dependent of several factors, e.g., present phases and crystal morphology. The microwave-assisted hydrothermal method (MAH) is a fast and efficient approach of synthesis to obtain semiconductor powders. However, the synthesis of monoclinic bismuth oxide (α-Bi₂O₃) with acicular morphology by MAH was not found in literature. In this paper, microcrystals of acicular α-Bi₂O₃ (monophasic) were successfully obtained by MAH using a synthesis temperature of 80°C for 0.5?h. X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron, and transmission electron microscopies showed the formation of a monoclinic structure (space group P21/c) with acicular morphology that grew along the [001] direction. The temperature and time necessary to synthetize acicular microcrystals were significantly lower than those found for acicular microcrystals obtained by conventional hydrothermal method.     

Facile synthesis of heterostructure NiO–SnO2 nanocomposite for selective electrochemical determination of l-cysteine

Journal of Materials Science: Materials in Electronics - In this present research, heterostructure NiO–SnO2 nanocomposite modified electrode was developed to determine l-cysteine molecule....     

Facile synthesis of Ca-doped manganite nanoparticles by a nonaqueous sol–gel method and their magnetic properties

Perovskite manganite La_1−xCa_xMnO₃ (x=1/3$x=1/3$, 1/2 and 2/3) nanoparticles with the average particle size of about 20 nm have been synthesized by a facile nonaqueous sol–gel method using methanol as a solvent and characterized by X-ray diffraction, transmission electron microscopy and superconducting quantum interference device magnetometer. Magnetic measurements reveal that although their bulk counterparts have quite different magnetic ground states, the three-nanosized samples exhibit similar ferromagnetic behaviors below about 270 K. This result implies that with the particle size reduced to nanoscale, the ferromagnetism for x=1/3$x=1/3$ is weaken, while it is enhanced, accompanied by the suppression of the charge ordering, for x=1/2$x=1/2$ and 2/3. Moreover, the exchange bias phenomena are observed in the two latter nanoparticles, which is of special interest for potential applications.     

Black nanocrystalline cubic zirconia: Manganese-stabilized c-ZrO2 prepared via the sol–gel method

Nanostructured manganese-stabilized cubic zirconia (MnSZ) powders, solid solutions of Zr_1−xMn_xO_2−yx = 0, 0.03, 0.06 and 0.09, were obtained via the sol–gel method. The doped phases crystallized at 500 °C into black cubic nanocrystalline zirconia.     

Crystal,magnetic and electric behaviour of CoMnxFe2−xO4 cubic ferrites

Six powder samples of CoMn _x Fe_2–x O₄ (O x 1) were synthesized by using a ceramic sintering technique. X-ray powder diffraction patterns were obtained and confirmed the presence of single-phase spinel structure with no evidence of impurities. Lattice constants were determined. Differential thermal analysis measurements showed no variation in crystal phase with temperature. AC conductivity measurements at the temperature range (300–950 K) and for the frequency range (10²–10⁵ Hz) were also carried out and the Néel transition temperatures for all samples were determined. Mössbauer effect patterns revealed magnetic ordering for all compositions at room temperature. The obtained spectra were successfully analysed into two Zeeman sextets, could be attributed to the tetrahedral and octahedral sites. The different Mössbauer effect parameters were deduced and discussed. Neutron diffraction measurements were also performed where oxygen parameters and cation distributions were determined, and magnetic structure were studied. All obtained results from the different techniques support the Néel model of ferrimagnetism for such compounds.