Capacitive and textural characteristics of hydrous manganese oxide prepared by anodic deposition

The amorphous hydrous manganese oxide (denoted as a-MnO_x·nH₂O) was anodically deposited from the MnSO₄ solutions of various pH values. The capacitive characteristics and stability of this oxide without and with annealing in air for 2 h up to 400 °C were systematically investigated in aqueous electrolytes through means of cyclic voltammetry (CV) and the constant-current charge-discharge method. The redox properties of a-MnO_x·nH₂O were strongly affected by the electrolytes employed and this oxide exhibited ideally capacitive behavior in 0.1 M Na₂SO₄ and 0.3 M KCl. The stability of this amorphous hydrous oxide was enhanced by the annealing treatment while its capacitance was gradually decreased with increasing the annealing temperature. The amorphous structure and surface morphologies of a-MnO_x·nH₂O with annealing at different temperatures were, respectively, examined in terms of the X-ray diffraction (XRD) patterns and scanning electron microscopic (SEM) photographs. The oxidation states of these a-MnO_x·nH₂O deposits were studied by X-ray photoelectron spectroscopy (XPS).     

Large-scale synthesis of WO3 nanoplates by a microwave-hydrothermal method

Tungsten oxide (WO₃) nanoplates were synthesized by a 270 W microwave-hydrothermal reaction of Na₂WO₄·2H₂O and citric acid (C₆H₈O₇·H₂O) in deionized water. X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), and selected area electron diffraction (SAED) were used to reveal the synthesis of WO₃ complete rectangular nanoplates in the solution of 0.2 g citric acid for 180 min, with O-W-O FTIR stretching modes at 819 and 741 cm⁻¹, and two prominent O-W-O Raman stretching modes at 804 and 713 cm⁻¹. The 2.71 eV indirect energy gap, and 430-460 nm blue emission wavelength range of WO₃ complete rectangular nanoplates were determined using UV-visible and photoluminescence (PL) spectrometers. The formation mechanism was also proposed according to the experimental results.     

Synthesis and characterization of In2S3 nanostructures via ultrasonic method in the presence of thioglycolic acid

In the present study, nanocrystalline In₂S₃ with different morphologies and particle sizes were obtained via an ultrasonic method by employing InCl₃·4H₂O, thioglycolic acid (TGA) and propylene glycol as In³⁺, sulfur source and solvent agent, respectively. Besides, the effects of preparation parameters such as time and power of ultrasonic irradiation, solvent, and surfactant on the morphology and particle size of the products were studied. The synthesis procedure is simple and facile for the preparation of structures with various morphologies. The morphology, structure, and composition of the as-synthesized nanostructures have been investigated by X-ray diffraction (XRD), energy dispersive X-ray analysis (EDX), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Optical properties of the as-prepared sample were investigated by photoluminescence (PL) and ultraviolet–visible (UV–vis) spectroscopy.     

Electrochemical and textural characterization of binary Ru-Sn oxides synthesized under mild hydrothermal conditions for supercapacitors

Hydrous ruthenium-tin oxides (denoted as (Ru-Sn)O₂·nH₂O) were synthesized under a mild hydrothermal condition. The mean particles size of pristine RuO₂·nH₂O, smaller than 3 nm, was decreased with the introduction of Sn into the precursor solutions while it is not significantly affected by varying the Sn content. The textual characteristics of (Ru-Sn)O₂·nH₂O were analyzed through means of X-ray diffraction (XRD), energy-dispersive spectroscopy (EDS), electron diffraction, X-ray photoelectron spectroscopy (XPS), and thermogravimetric analyses (TGA). From the ideal capacitive behavior of pristine oxides with the Ru content ≥40 at.%, hydrothermal synthesis favored the formation of hydrous oxides with a novel structure providing excellent pathways for electron hopping and proton diffusion/exchange during the charge storage/delivery process. The introduction of tin oxide was demonstrated to successfully promote the utilization of oxyruthenium species, reaching a maximum C_S,Ru of ca. 830 F/g for pristine Ru_0.6Sn_0.4O₂·nH₂O (measured at 25 mV/s).     

Synthesis and characterization of ZnxMg1 − xGa2O4:Co fabricated by low-temperature burning method

A series of Zn_xMg_1 − xGa₂O₄:Co²⁺ spinels (x = 0, 0.25, 0.5, 0.75, and 1.0) was successfully produced through low-temperature burning method by using Mg(NO₃)₂·4H₂O, Zn(NO₃)₂·6H₂O, Ga(NO₃)₃·6H₂O, CO(NH₂)₂, NH₄NO₃, and Co(NO₃)₂·6H₂O as raw materials. The product was characterized by X-ray diffraction, transmission electron microscopy, and photoluminescence spectroscopy. The product was not merely a simple mixture of MgGa₂O₄ and ZnGa₂O₄; rather, it formed a solid solution. The lattice constant of Zn_xMg_1 − xGa₂O₄:Co²⁺ (0 ≤ x ≤ 1.0) crystals has a good linear relationship with the doping density, x. The synthesized products have high crystallinities with neat arrays. Based on an analysis of the form and position of the emission spectrum, the strong emission peak around the visible region (670 nm) can be attributed to the energy level transition [⁴T₁(⁴P) → ⁴A₂(⁴F)] of Co²⁺ in the tetrahedron. The weak emission peak in the near-infrared region can be attributed to the energy level transition [⁴T₁(⁴P) → ⁴T₂(⁴F)] of Co²⁺ in the tetrahedron.     

Effects of substrates on the capacitive performance of RuOx·nH2O and activated carbon-RuOx electrodes for supercapacitors

The electrochemical energy storage and delivery on the electrodes composed of hydrous ruthenium oxide (RuO_x·nH₂O) or activated carbon-hydrous ruthenium oxide (AC-RuO_x) composites are found to strongly depend on the substrate employed. The contact resistance at the active material-graphite interface is much lower than that at the active material-stainless steel (SS) mesh interface. Thin films of gold plus RuO_x·nH₂O deposited on SS meshes (RuO_x/Au/SS) are found to greatly improve the poor contact between SS meshes and electrode materials. The maximum specific capacitance (C_S,RuOx) of RuO_x·nH₂O, 1580 F g⁻¹ (measured at 1 mV s⁻¹), very close to the theoretic value, was obtained from an AC-RuO_x/RuO_x/Au/SS electrode with 10 wt.% sol-gel-derived RuO_x·nH₂O annealed in air at 200 °C for 2 h. The highly electrochemical reversibility, high-power characteristics, good stability, and improved frequency response of this AC-RuO_x/RuO_x/Au/SS electrode demonstrate its promising application potential in supercapacitors. The ultrahigh specific capacitance of RuO_x·nH₂O probably results from the uniform size distribution of RuO_x·nH₂O nanoparticles, ranged from 1.5 to 3 nm which is clearly observed from the high-resolution transmission electron microscopy (HRTEM).     

Crystallization kinetics of lanthanum monoaluminate (LaAlO3) nanopowders prepared by co-precipitation process

Lanthanum monoaluminate (LaAlO₃) nanopowders were synthesized using La(NO₃)₃·6H₂O and Al(NO₃)₃·6H₂O as starting materials by a co-precipitation method. The crystallization kinetics of the LaAlO₃ nanopowders has been investigated by using differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). The XRD results and SAED patterns show that the rhombohedral LaAlO₃ nanopowders have been obtained when the precipitates as calcined at 1092 K for 10 min. The activation energy for the crystallization of the rhombohedral LaAlO₃ nanopowders is determined as 286.75 kJ/mol by a non-isothermal method. The TEM examination shows that the rhombohedral LaAlO₃ has a spherical morphology with the size ranging from 30 to 50 nm.     

Soft template synthesis of mesoporous Co3O4/RuO2·xH2O composites for electrochemical capacitors

Co₃O₄/RuO₂·xH₂O composites with various Ru content (molar content of Ru = 5%, 10%, 20%, 50%) were synthesized by one-step co-precipitation method. The precursors were prepared via adjusting pH of the mixed aqueous solutions of Co(NO₃)₂·6H₂O and RuCl₃·0.5H₂O by using Pluronic123 as a soft template. For the composite with molar ratio of Co:Ru = 1:1 annealed at 200 °C, Brunauer-Emmet-Teller (BET) results indicated that the composite showed mesoporous structure, and the specific surface area of the composite was as high as 107 m² g⁻¹. The electrochemical performances of these composites were measured in 1 M KOH electrolyte. Compared with the composite prepared without template, the composite with P123 exhibited a higher specific capacitance. When the molar content of Ru was rising, the specific capacitance of the composites increased significantly. It was also observed that the crystalline structures as well as the electrochemical activities were strongly dependent on the annealing temperature. A capacitance of 642 F/g was obtained for the composite (Co:Ru = 1:1) annealed at 150 °C. Meanwhile, the composites also exhibited good cycle stability. Besides, the morphologies and textural characteristic of the samples were also investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM).     

The solubility of selenate-AFt (3CaO·Al2O3·3CaSeO4·37.5H2O) and selenate-AFm (3CaO·Al2O3·CaSeO4·xH2O)

The Se(VI)-analogues of ettringite and monosulfate, selenate-AFt (3CaO·Al₂O₃·3CaSeO₄·37.5H₂O), and selenate-AFm (3CaO·Al₂O₃·CaSeO₄·xH₂O) were synthesised and characterised by bulk chemical analysis and X-ray diffraction. Their solubility products were determined from a series of batch and resuspension experiments conducted at 25 °C. For selenate-AFt suspensions, the pH varied between 11.37 and 11.61, and a solubility product, log K_so=61.29±0.60 (I=0 M), was determined for the reaction 3CaO·Al₂O₃·3CaSeO₄·37.5H₂O+12 H⁺⇔6Ca²⁺+2Al³⁺+3SeO₄²⁻+43.5H₂O. Selenate-AFm synthesis resulted in the uptake of Na, which was leached during equilibration and resuspension. For the pH range of 11.75 to 11.90, a solubility product, log K_so=73.40±0.22 (I=0 M), was determined for the reaction 3CaO·Al₂O₃·CaSeO₄·xH₂O+12 H⁺⇔4Ca²⁺+2Al³⁺+SeO₄²⁻+(x+6)H₂O. Thermodynamic modelling suggested that both selenate-AFt and selenate-AFm are stable in the cementitious matrix; and that in a cement limited in sulfate, selenate concentration may be limited by selenate-AFm to below the millimolar range above pH 12.     

One-step room-temperature solid-phase synthesis of ZnFe2O4 nanomaterials and its excellent gas-sensing property

ZnFe₂O₄ nanomaterials have been synthesized by simple one-step solid-phase chemical reaction between Zn(CH₃COO)₂·2H₂O, FeCl₃·9H₂O and NaOH within a very short time at room temperature. The solid-phase products were characterized by X-ray diffraction, energy-dispersive X-ray spectroscopy, thermogravimetic analysis, transmission electron microscopy and scanning electron microscopy. Results indicated that the particle size of product can be obviously let up and the agglomeration phenomenon can be improved by the surfactant. Moreover, the ZnFe₂O₄ nanomaterials were applied in gas sensor and exhibited much better sensing performance than bulk ZnFe₂O₄. The as-prepared ZnFe₂O₄ nanomaterials have high sensitivity, good selectivity and fast response/recovery characteristic for ethanol and hydrogen sulfide. The improved ZnFe₂O₄ nanomaterials have high response value of 21.5 and 14.8 for ethanol and hydrogen sulfide in the optimized operating temperature of 332 °C and 240 °C, respectively. The response and recovery time was found to be within 4 s and 14 s for ethanol, while 7 s and 25 s for hydrogen sulfide.     

Microwave hydrothermal synthesis of Sr doped ZnO crystallites with enhanced photocatalytic properties

Pure and Sr²⁺ doped ZnO crystallites were successfully synthesized via a microwave hydrothermal method using Zn(NO₃)₂·6H₂O and Sr(NO₃)₂·6H₂O as source materials. The phase and microstructure of the as-prepared Zn_1−xSr_xO crystallites were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Ultraviolet–visible spectrum (UV–vis) and photochemical reaction instrument were used to analyze the photocatalytic properties of the particles. XRD results show that the diffraction peaks of the as-prepared Zn_1−xSr_xO crystallites shifted slightly toward lower 2θ angle with the increasing of Sr²⁺ doping concentration from 0% to 0.3%. The pure ZnO crystallites with lamellar structure are found transforming to a hexagonal columnar morphology with the increase of Sr²⁺ doping concentration. UV–vis analysis shows that the particles have a higher absorption in UV region with a slightly decreased of optical band (E_g) gap. The photocatalytic activity of Sr²⁺ doped ZnO crystallites was evaluated by the Rhodamine B (RhB) degradation in aqueous solution under visible-light irradiation. Compared with the pure ZnO particles, the photocatalytic properties of the Sr²⁺ doped ZnO crystallites are obviously improved. The photocatalysis experiment results demonstrate that the 0.1% Sr²⁺ doped ZnO exhibits the best photocatalytic activity for the degradation of Rhodamine B.     

The influence of PbO modification on the kinetics of the 4PbO·PbSO4 lead-acid battery paste formation

The influence of PbO modification on the formation of 4PbO·PbSO₄ paste is determined by X-ray diffraction analysis and scanning electron microscopy. The paste was prepared from tetragonal PbO, orthorhombic PbO and several mixtures of both oxides at 80° C and a H₂SO₄/PbO ratio of 6 wt%.The reaction scheme of 4PbO·PbSO₄ formation depends on the PbO modification. When tetragonal PbO is used, 3PbO·PbSO₄·H₂O crystals are obtained first and then 4PbO·PbSO₄. If the initial oxide is orthorhombic PbO, PbSO₄, PbO·PbSO₄ and 3PbO·PbSO₄·H₂O are formed successively. When the correct ratio of 3PbO·PbSO₄·H₂O, orthorhombic PbO and tetragonal-PbO is achieved in the paste then 4PbO·PbSO₄ formation begins. This ratio is reached most quickly if tetragonal PbO is present at 30–60wt% in the initial mixture of both modifications.     

Templated Ru/Se/C electrocatalysts for oxygen reduction

Highly porous Ru/Se/C electrocatalysts have been successfully synthesized via a template-based method, which was carried out by the impregnation of a hard template (silica gel) with a mixture of RuCl₃·xH₂O, SeO₂ and sucrose dissolved in water. The resulting Ru/Se/C catalysts show good catalytic activity for oxygen reduction in acidic media. The electrocatalysts are believed to consist of selenium-modified ruthenium nanoparticles, which are embedded in a high surface area carbon matrix. The structural properties of the prepared Ru/Se/C electrocatalysts were investigated using nitrogen physisorption measurements, X-ray diffraction and transmission electron microscopy. The elemental composition of prepared Ru/Se/C electrocatalysts was determined using electron microprobe. The catalytic activity was tested using the rotating-ring-disk-electrode technique in 0.1 M HClO₄ solution at room temperature.     

Graphene nanosheets-tungsten oxides composite for supercapacitor electrode

Graphene nanosheets-tungsten oxides (tungsten oxide/tungsten oxide hydrate mixture) (GNS-W) composite was successfully synthesized using a facile approach. WO₃/WO₃·H₂O mixtures were deposited on the graphene nanosheets (GNS) to form the GNS-W composite. The GNS-W composite was characterized by X-ray diffraction (XRD), Raman spectrum, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The as-prepared GNS-W composite was directly fabricated into a supercapacitor electrode for potential energy storage application, and electrochemically tested by cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy. The GNS-W composite electrode exhibits a better electrochemical performance than that of the WO₃/WO₃·H₂O mixtures electrode. A high specific capacitance of about 143.6 F g⁻¹ at a current density of 0.1 A g⁻¹ for the GNS-W composite delivers significant improvement than that for the WO₃/WO₃·H₂O mixtures and GNS electrodes. The impedance studies also suggest that the GNS-W composite electrode shows the lower resistance and high conductivity due to the good interaction between the graphene nanosheets and the WO₃/WO₃·H₂O mixtures. The good electrochemical performance for the GNS-W composite may be attributed to the interaction between the WO₃/WO₃·H₂O mixtures and the edges of graphene nanosheets, which increases the ion diffusion rate as well as the conductivity.     

Synthesis of nano-crystalline NiO-YSZ by microwave-assisted combustion synthesis

Nano-crystalline NiO-YSZ composite powders have been successfully prepared by microwave-assisted combustion of a gel derived from an aqueous solution containing ZrO(NO₃)₂·6H₂O ,Y(NO₃)₃·6H₂O, Ni(NO₃)₂·6H₂O and glycine. The as-prepared powders were examined using X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM) techniques. It was found that the process took only a few seconds to obtain NiO-YSZ composite powders. The as synthesized composite powder was a homogeneous mixture of YSZ, NiO and Ni phases with crystallite size of 24.2, 33.6 and 25.3 nm respectively.     

Mineralogical characteristics of Ettringites synthesized from solutions and suspensions

Due to the wide technical importance of Ettringite (3CaO·Al₂O₃·3CaSO₄·32H₂O) in hydrated cement based systems, four different synthesis methods were applied to get a better overview on how and under what favoring conditions Ettringite can be formed. In the first step different precipitation methods resulting in Ettringite were established. For all methods Al³⁺ was supplied by aqueous CO₂-free solution of Al₂(SO₄)₃·18H₂O. As a source of CaO-supply a clear solution and otherwise a Ca(OH)₂-suspension was utilized. Four synthesis routes with and without sucrose were employed.Variation of reaction parameter like temperature, time of reaction, pH-value of synthesis solution and influence of additional Gypsum were investigated. The qualitative phase analysis was performed by X-ray diffraction method (XRD). Morphological aspects of some synthesis products were studied by scanning electron microscopy (SEM). Finally lattice and structural parameter of the Ettringites were determined by refinement of XRD-pattern using the Rietveld-Method.     

Bioethanol production from corn meal by simultaneous enzymatic saccharification and fermentation with immobilized cells of Saccharomyces cerevisiae var. ellipsoideus

The simultaneous enzymatic saccharification and fermentation (SSF) of corn meal using immobilized cells of Saccharomycescerevisiae var. ellipsoideus yeast in a batch system was studied. The yeast cells were immobilized in Ca-alginate by electrostatic droplet generation method. The process kinetics was assessed and determined and the effect of addition of various yeast activators (mineral salts: ZnSO₄ · 7H₂O and MgSO₄ · 7H₂O, and vitamins: Ca-pantothenate, biotin and myo-inositol) separately or mixed, was investigated. Taking into account high values of process parameters (such as ethanol concentration, ethanol yield, percentage of the theoretical ethanol yield, volumetric productivity and utilized glucose) and significant energy savings the SSF process was found to be superior compared to the SHF process. Further improvement in ethanol production was accomplished with the addition of mineral salts as yeast activators which contributed to the highest increase in ethanol production. In this case, the ethanol concentration of 10.23% (w/w), percentage of the theoretical ethanol yield of 98.08%, the ethanol yield of 0.55 g/g and the volumetric productivity of 2.13 g/l·h were obtained.     

Atom transfer radical polymerizations of methyl methacrylate catalyzed by EBiB/SnCl2·2H2O(FeCl2·4H2O)/FeCl3·6H2O/MA5-DETA systems

The ATRP of methyl methacrylate (MMA) with the system of FeCl₂·4H₂O, N,N,N′,N″,N″-penta(methyl acylate)diethylenetriamine (MA₅-DETA) and ethyl 2-bromoisobutyrate (EBiB) showed high activity and is not well-controlled. The addition of a certain amount of FeCl₃·6H₂O as the additive into the above system results in the decrease of the polymerization rate and the improvement of the controllability. When SnCl₂·2H₂O was added instead of FeCl₂·4H₂O, a novel catalyst system SnCl₂·2H₂O/FeCl₃·6H₂O/EBiB/MA₅-DETA formed shows better controllability, higher catalytic activity and higher initiating efficiencies (more than 90%) in comparison with the system FeCl₂·2H₂O/FeCl₃·6H₂O/EBiB/MA₅-DETA. The polydispersities of the polymers kept range from M_w/M_n=1.18-1.26. The real active species in the new system is Fe (II) formed from the reaction of FeCl₃·6H₂O with the active radical species produced from the reaction of SnCl₂·2H₂O with EBiB.     

Textural and pseudocapacitive characteristics of sol-gel derived RuO2·xH2O: Hydrothermal annealing vs. annealing in air

Hydrous ruthenium dioxide (RuO₂·xH₂O) prepared in a modified sol-gel process was subjected to annealing in air and water at various temperatures for supercapacitor applications. The textural and pseudocapacitive characteristics of RuO₂·xH₂O annealed in air and water were systematically compared to show the benefits of annealing in water (denoted as hydrothermal annealing). An important concept that hydrothermal annealing effectively restricts condensation of hydroxyl groups within nanoparticles, inhibits crystal growth, and maintains high water content of RuO₂·xH₂O is demonstrated in this work. The unique textural characteristics of hydrothermally annealed RuO₂·xH₂O are attributable to the high-pressured, water-enriched surroundings which restrain coalescence of RuO₂·xH₂O nanocrystallites. The crystalline, hydrous nature of hydrothermally annealed RuO₂·xH₂O favors the utilization of active species in addition to a merit of minor dependence of specific capacitance on the scan rate of CV for pseudocapacitors. As a result, RuO₂·xH₂O with hydrothermal annealing at 225 °C for 24 h exhibits 16 wt.% water, an average particle size of about 7 nm, and specific capacitance of ca. 390 F g⁻¹.     

Biomimetic synthesis of spherical nano-hydroxyapatite in the presence of polyethylene glycol

Spherical nano-hydroxyapatite (nano-HA) was synthesized successfully by a biomimetic method using Ca(NO₃)₂·4H₂O and (NH₄)₃PO₄·3H₂O as reagents in the presence of polyethylene glycol (PEG). The crystalline phase, microstructure, chemical composition, and morphology of the obtained samples were characterized by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and transmission electron microscopy (TEM). The results show that spherical nano-HA with diameter of 30–50 nm can be synthesized in the presence of a certain concentration (2–6%) of PEG. The crystallinity of HA powder synthesized in the presence of PEG was higher than that synthesized in the absence of PEG, but the crystallinity of HA reduced with increasing the concentration of PEG. The electrical conductivity (EC) of the solution revealed that PEG reduced the transfer rate of Ca²⁺ in the process of HA crystallization, indicating the interaction between PEG and HA. The possible mechanism of formation spherical nano-HA was discussed.