Facile synthesis and catalytic properties of single crystalline β-MnO2 nanorods

Single-crystalline β-MnO₂ nanorods were successfully synthesized through facile reflux treatment of KMnO₄ and MnSO₄ in HNO₃ solution. TEM and SEM images show that the synthesized β-MnO₂ nanorods exhibited diameters of 20–50 nm, and lengths that ranged from approximately 0.5 to 2.0 μm with decreasing HNO₃ concentrations from 0.8 to 0.1 mol/L. The β-MnO₂ nanorods underwent three primary evolutionary stages over time. They exhibited excellent catalytic properties for the degradation of methylene blue (MB) by a Fenton-like reaction.     

A kinetic study of electrochemical lithium insertion in nanosized rutile β-MnO2 by impedance spectroscopy

The kinetics of the electrochemical lithium insertion reaction in nano-sized rutile β-MnO₂ has been investigated using ac impedance spectroscopy. The experimental kinetic data are obtained for a rutile compound synthesized by ball-milling the powder produced from the heat treatment of manganese nitrate salts. The results are discussed as a function of the Li content for 0 < x < 0.6 and the number of cycles in the 4.1–2 V window. From a comparison with data obtained on the micro-sized oxide, an improved kinetics is found with D_Li values for the apparent chemical diffusion coefficient of lithium much higher by one order of magnitude than in microsized oxide. Impedance behaviour of the ball-milled rutile β-MnO₂vs cycles demonstrates a new system takes place from the second cycle, characterized by a significant improvement of Li diffusion by a factor 5 and a cathode impedance which decreases by a factor 2, remaining thereafter unchanged during cycling.     

Bundle-shaped β-NaYF4 microrods: Hydrothermal synthesis,Gd-mediated downconversion luminescence and ratiometric temperature sensing

In this study, bundle-shaped β-NaYF₄ microrods with uniform morphology and good monodispersity were successfully synthesized via a facile, template-free and environmentally-friendly hydrothermal route. According to the time-dependent experimental results, the formation mechanism for the crystal phase and shape evolution process has been proposed via the Ostwald-ripening process. Under single wavelength irradiation at 250?nm, intense multi-color downconversion emissions can be obtained by co-doping Ce³⁺, Gd³⁺ and X³⁺ (X = Eu, Tb and Dy) into the as-synthesized β-NaYF₄ crystals, in which Gd³⁺ plays an intermediate role in transferring the excitation energy from sensitizer Ce³⁺ to activators X³⁺. Furthermore, the temperature-dependent emission behaviors of β-NaY_0.8Gd_0.2F₄:Ce³⁺/X³⁺ dual-emitting products have been systemically investigated to explore their possible application in self-calibrated optical thermometry. Impressively, the high temperature sensitivity, good signal discriminability and excellent thermal stability of the investigated dual-emitting phosphors making them a promising candidate for temperature sensing.     

Hydrothermal synthesis of α-SnWO4: Application to lithium-ion battery and photocatalytic activity

The high capacity anode material is required to replace the most commonly used anode - graphite to keep up the global demand to achieve the goal. Multi-metal oxide has gained keen attention for its higher theoretical capacity and relatively stable than a single metal oxide. α-SnWO₄ has a theoretical capacity of 850 mAh g^?1 which is greater than graphite (372 mAh g^?1). α-SnWO₄ has been synthesized through low-temperature hydrothermal method using tin chloride and sodium tungstate as a precursor in acidic medium (succinic acid) at 200 °C for 12 h. The obtained product has been characterized using various analytical tools such as XRD, FT-IR, UV-DRS, BET, PL, SEM, and HR-TEM. XRD analysis shows the orthorhombic phase with a crystallite size of ~25 nm α-SnWO₄has been examined as an electrode material for Li-ion battery (LIB) and displays an initial discharge capacity of 985 mAh g^?1. Columbic efficiency close to 100% has been observed for 100 cycles. The stability of the electrode material was studied at different C-rates. Band-gap calculated using UV-DRS (Eg = 1.9 eV) shows that α-SnWO₄ is a good candidate for photocatalytic degradation. Results of the photocatalytic experiment using methylene blue (MB) as a model pollutant in an aqueous medium shows good results. The above applications show that α-SnWO₄ is multifunctional materials for diverse applications.     

Preparation and characterization of lithium λ-MnO2 ion-sieves

Lithium λ-MnO₂ ion-sieves were prepared from spinel LiMn₂O₄ via treatment with nitric acid. The LiMn₂O₄ was synthesized by a solid state reaction between LiOH·H₂O and MnO₂. The effects of the calcination time and temperature on the preparation of the LiMn₂O₄ precursor and the lithium ion-sieve were investigated. In addition, the Li⁺ extraction ratio, the Mn²⁺ dissolving ratio and the adsorption properties of the lithium ion-sieve were all measured. The lithium ion-sieve had a high exchange capacity and was selective for Li⁺. Specifically, at pH= 13, the ion exchange capacity of Li⁺ was 30.9 mg/g in 10 mmol/L LiCl solution and the lithium extraction ratio and manganese dissolving ratio were 95% and 25%, respectively.     

β-Keto sulfones: preparation and application in organic synthesis

The review summarizes a survey of recent advances and contributions to the methods of synthesis, chemical properties and application of β-keto sulfones with the main focus on the their increasingly growing demand as starting substrates and intermediates incorporated in the syntheses of various classes of organic compounds.     

Single-phase silicocarnotite synthesis in the subsystem Ca3(PO4)2–Ca2SiO4

In the last years, the addition of silicon to hydroxyapatite and tricalcium-phosphate materials is being widely studied, due to the well-known influence of silicon on bone formation. Silicocarnotite (Ca₅(PO₄)₂SiO₄) presents a structure type carnotite, very close to hydroxyapatite, with a wide range of Ca²⁺, SiO₄⁴⁻ and PO₄³⁻ solid solutions. These characteristics make silicocarnotite attractive as potential biomaterial.     

Hydrothermal synthesis and characterization studies of α-Fe2O3/MnO2 nanocomposites for energy storage supercapacitor application

In this present study, semiconductor magnetic α-Fe₂O₃/MnO₂ nanocomposites (NCs) were prepared by a facile hydrothermal (HT) method. The crystallographic structure, morphology, chemical configuration and magnetic features were analysed by X-ray powder diffraction (XRD), high resolution scanning electron microscope (HR-SEM), energy dispersive X-ray analysis (EDX), transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and vibrating sample magnetometer (VSM) analyses. The as-prepared NCs were used as an electrode in energy storing supercapacitor was systematically examined. The electrochemical deeds of α-Fe₂O₃/MnO₂ NCs was analysed by cyclic voltammetry (C–V) and galvanostatic charge–discharge (GCD) tests. The CV analysis of the NCs electrode showed a distinctive pseudocapacitive behaviour in 1 M KOH solution. The NCs electrode reveals enhanced specific capacitance compared to plain α-Fe₂O₃ and MnO₂ nanoparticles (NPs) and generates high specific capacitance of 216.35 Fg⁻¹. Pseudocapacitor obtains of energy density 135.42 Wh kg⁻¹ at power density of 6.399 kW kg⁻¹, indicating the as-prepared α-Fe₂O₃/MnO₂ NCs shows noteworthy high-energy, specific capacitance, power densities and long-standing cyclic stability with 89.2% of preliminary capacitance reserved at 1A g⁻¹ after 10000 cycles in judgement with the pure α-Fe₂O₃ and MnO₂ NPs electrode. The α-Fe₂O₃/MnO₂ NCs electrode having noteworthy electrochemical characteristics performance renders promising applications in energy storing systems.     

Synthesis of tuneable porous hematites (α-Fe2O3) for gas sensing and lithium storage in lithium ion batteries

Tuneable porous α-Fe₂O₃ materials were prepared by using a selective etching method. The structure and morphology of the as-prepared porous hematites have been systematically characterised by X-ray diffraction, field emission scanning electron microscope, and transmission electron microscope. We found that the pore size and pore volume can be controlled by adjusting the etching time during the synthesis process. The porous hematites have been applied for gas sensing and lithium storage in lithium ion cells. The porous α-Fe₂O₃ materials demonstrated a reversible lithium storage capacity of 1269 mAh/g. When used as a sensing material in gas sensors, porous α-Fe₂O₃ exhibited a superior sensitivity towards toxic and flammable gases.     

Effect of specific surface area on capacitance in asymmetric carbon/α-MnO2 supercapacitors

α-MnO₂ has been made using a solid state synthesis and the specific surface area then modified through milling. The formation of α-MnO₂ (specific surface area 96 m² g⁻¹) has been studied by SEM and powder XRD prior to milling. Electrode films (cast using MnO₂, graphite and PVDF) have been investigated using N₂ sorption at 77 K and show a more complex relationship than their parent oxides. Specific capacitances of 235 F g⁻¹ were observed in cyclic voltammetry studies in (NH₄)₂SO₄ (aq.) electrolyte. Good cyclability was observed in hybrid C/MnO₂ cells investigated through both galvanostatic and electrochemical impedance techniques. The specific capacitances of the cells were found to correlate with S_BET of the electrode films and not that of the parent MnO₂ powders.     

Microemulsion-mediated hydrothermal growth of pagoda-like Fe3O4 microstructures and their application in a lithium–air battery

This paper reported the growth of novel pagoda-like Fe₃O₄ particles via a facile microemulsion-mediated hydrothermal procedure. The chemical compositions and morphologies of the as-grown Fe₃O₄ particles were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), and field emission scanning electron microscopy (FE-SEM). The morphologies of the as-prepared sample evolved from pagoda-like to pinwheel-like to flower-like shapes with increasing reaction time. In addition, the NaOH concentration and polyethylene glycol (PEG)-2000 had key effects on the formation of the final product. The electrocatalytic properties of the prepared pagoda-like micro-Fe₃O₄, as catalytic materials for a lithium–air battery, were further evaluated by galvanostatic charge/discharge cycling and electrochemical impedance spectrometry (EIS). Results showed that the cell displayed an initial discharge capacity of 1429 mA h g⁻¹ at a voltage of 1.5–4.5 V at 100 mA g⁻¹.     

TiO2 promoted Co/SiO2 catalysts for Fischer–Tropsch synthesis

The addition of small amount of TiO₂ to silica-supported cobalt catalysts significantly increasing the dispersion of cobalt and Co metallic surface area resulting in the remarkable enhancement of the Fisher–Tropsch synthesis (FTS) activity in the slurry-phase reaction. The addition of TiO₂ adjusted the interaction between cobalt and silica support quite well to realize the favorite dispersion and reduction degree of supported cobalt, leading to high catalytic activity in FTS. The properties of various catalysts were characterized by in-situ DRIFT, XRD, TPR, N₂ physisorption and H₂ chemisorption.     

α- and β-AgVO3 polymorphs as photoluminescent materials: An example of temperature-driven synthesis

Controlling the synthesis of a given polymorph of an inorganic material is a further step in the design of property and function. In this letter, we report for the first time a simple procedure to effectively control the reversible transformation between the crystalline polymorphs α-AgVO₃ and β-AgVO₃. Photoluminescence emission (PL) performance is analyzed; at low temperatures (up to 35 °C) when α-AgVO₃ is formed the PL emission is red, while at temperatures larger than 45 °C when β-AgVO₃ is obtained the color of emission PL emission goes from green to blue. The findings highlight the ability of temperature to dramatically alter the nature of phase transformation at the atomic level. The phase transformation is driven by the short-range structural and electronic changes of [VO₄] and [AgO_x] (x = 5, 6, and 7) clusters (building blocks of both monoclinic structures), and hence is dependent on the temperature employed during synthesis. These outcomes clearly demonstrate that the AgVO₃ crystals exhibited appropriate activity for application in visible lamps, displays, and other optical devices.     

Investigation of the effect of ZrO2 and ZrO2/Al2O3 additions on the hot-pressing and properties of equimolecular mixtures of α- and β-Si3N4

In this work, hot-pressing of equimolecular mixtures of α- and β-Si₃N₄ was performed with addition of different amounts of sintering additives selected in the ZrO₂–Al₂O₃ system. Phase composition and microstructure of the hot-pressed samples was investigated. Densification behavior, mechanical and thermal properties were studied and explained based on the microstructure and phase composition. The optimum mixture from the ZrO₂–Al₂O₃ system for hot-pressing of silicon nitride to give high density materials was determined. Near fully dense silicon nitride materials were obtained only with the additions of zirconia and alumina. The liquid phase formed in the zirconia and alumina mixtures is important for effective hot-pressing. Based on these results, we conclude that pure zirconia is not an effective sintering additive. Selected mechanical and thermal properties of these materials are also presented. Hot-pressed Si₃N₄ ceramics, using mixtures from of ZrO₂/Al₂O₃ as additives, gave fracture toughness, K_IC, in the range of 3.7–6.2 MPa m^1/2 and Vicker hardness values in the range of 6–12 GPa. These properties compare well with currently available high performance silicon nitride ceramics. We also report on interesting thermal expansion behavior of these materials including negative thermal expansion coefficients for a few compositions.     

Fast synthesis of MgAl2O4‒W and MgAl2O4‒W‒W2B composite powders by self-propagating high-temperature synthesis reactions

MgAl₂O₄?W and MgAl₂O₄?W?W₂B composite powders were obtained rapidly in a single step by self-propagating high-temperature synthesis of WO₃?Mg?xAl₂O₃ and WO₃?B₂O₃?Mg?yAl₂O₃ systems. The addition of various Al₂O₃ contents (x and y-values) to the starting materials was considered as the main synthesis parameter. Thermodynamic calculations revealed that the adiabatic temperature of both systems was decreased with increasing Al₂O₃ content. The XRD results indicated that after acid leaching of the WO₃?Mg?xAl₂O₃ combustion products, W and MgAl₂O₄ were formed as the main phases and WO₂, MgWO₄ and Al₂O₃ as the minor constituents in the final composite. On the other hand, MgAl₂O₄?W composites were synthesized in the WO₃?B₂O₃?Mg?yAl₂O₃ system at y<1.4 mol. By increasing the y-value to 2.1 mol, W₂B was formed as a new product leading to production of MgAl₂O₄?W?W₂B composite. The formation of spinel was confirmed by the Fourier transformed infrared spectroscopy analysis. Microstructure observations represented the uniform distribution of MgAl₂O₄ blocks within the fine spherical W particles. The melting of Al₂O₃ was found as a vital step for rapid synthesis of MgAl₂O₃ by the SHS route. Finally, the possible formation mechanism of MgAl₂O₄ during the combustion synthesis was proposed.     

Densification and characterization of SiO2B2O3CaOMgO glass/Al2O3 composites for LTCC application

A glass/ceramic composite using lead-free low melting glass (SiO₂B₂O₃CaOMgO glass) with Al₂O₃ fillers was investigated. X-ray diffraction analysis revealed that the anorthite and cordierite phase appeared in the sintered composites. The dilatometric analysis showed that the onset of shrinkage took place at ∼624 °C for all the samples and the onset temperature was independent on the content of glass. The low melting glass significantly promoted densification of the composites and lowered the sintering temperature to ∼875 °C. The addition of 50 wt% glass sintered at 875 °C showed ε_r of 7.3, tan δ of 1.15×10⁻³, TEC of 5.41 ppm/°C, thermal conductivity of 3.56 W/m °C, and flexural strength of 184 MPa. The results showed that the SiO₂B₂O₃CaOMgO glass/Al₂O₃ composites were strong potential candidates for low temperature cofired ceramic substrate applications.     

Direct conversion of β-Ga2O3 thin films to β-Ga2O3 nanowires by annealing in a hydrogen atmosphere

We report the annealing process of Au/β-Ga₂O₃ thin films in a hydrogen atmosphere leading to a direct conversion of β-Ga₂O₃ thin films to β-Ga₂O₃ nanowires (NWs). Annealing in a hydrogen atmosphere results in the evaporation of β-Ga₂O₃ thin films, which are subsequently converted to β-Ga₂O₃ NWs through the vapor-liquid-solid (VLS) process assisted by Au nanocrystals. The VLS growth starts at 600?°C and progresses with increase in the annealing temperature to 800?°C. β-Ga₂O₃ NWs are formed on the surface of the host β-Ga₂O₃ thin films, resulting in the formation of a homogeneous β-Ga₂O₃ NW/β-Ga₂O₃ thin film structure. Based on structural analyses using X-ray diffraction, scanning electron microscopy, and transmission electron microscopy, a possible mechanism for the growth of β-Ga₂O₃ NWs is presented.     

Hydrogen-bond mediated and concentrate-dependent NaHCO3 crystal morphology in NaHCO3–Na2CO3 aqueous solution: Experiments and computer simulations

Adding Na₂CO₃ to the NaHCO3cooling crystallizer, using the common ion effect to promote crystallization and improve product morphology, is a new process recently proposed in the literature. However, the mechanism of the impact of Na₂CO₃ on the crystal morphology is still indeterminate. In this work, the crystallization of NaHCO₃ in water and Na₂CO₃ –NaHCO₃ aqueous solution was investigated by experiments and ...     

Combustion synthesis of β-SnWO4-rGO: Anode material for Li-ion battery and photocatalytic dye degradation

This article reports the synthesis β-SnWO₄–rGO nanocomposite (NC) by a simple solution combustion method followed by low temperature hydrothermal method. The β-SnWO₄–rGO NC has been characterized using various analytical tools such as X-ray diffraction (XRD), Raman spectroscopy, Scanning Electron Microscopy (SEM), High-Resolution Transmission Electron Microscopy (HR-TEM), Ultraviolet-Differential reflectance spectroscopy (UV-DRS). X-ray diffraction pattern shows the formation of cubic structured β-SnWO₄ nanoparticles (NPs) and Raman spectrum shows the presence of rGO in the composite. Transmission Electron Microscopy image shows that SnWO₄ NPs were embedded on the surface of rGO. β-SnWO₄ NPs and β-SnWO₄-rGO NC has been examined as an electrode material for Li-ion battery (LIB). β-SnWO₄ NPs and β-SnWO₄-rGO NC displays an initial discharge capacity of 1351 mAhg^?1 and 1662 mAhg^?1 which is about 23% increase in capacity. Electrochemical performance of β-SnWO₄-rGO NC at different current densities proves that it is one of the good candidates as an electrode material for LIB. β-SnWO₄-rGO NC shows enhanced photocatalytic activity against rose bengal (RB) and methylene blue (MB) compared to pure β-SnWO₄ NPs.