Synthesis of Zn2SnO4 anode material by using supercritical water in a batch reactor

Zn₂SnO₄ anode powders were successfully synthesized using supercritical water (SCW) and metal salt solutions with 10 min reaction time. Effect of NaOH concentration, Zn to Sn ratio, and synthesis temperature were studied with a SCW batch reactor. X-ray diffraction (XRD), scanning electron microscopy (SEM), and charge/discharge cycling tests were employed to characterize the physical properties and electrochemical performance of the as-prepared samples. Alkaline solution concentration and synthesis temperature played a key role in the production of single-phase Zn₂SnO₄ powders. At a solution concentration of 0.3 M NaOH and a molar ratio of Zn:Sn = 2:1 at 400 °C and 30 MPa, the average size range of the pure Zn₂SnO₄ powders was 0.5-1.0 μm, and the morphology was nearly uniform and cubic-like in shape. The initial specific discharge capacity of the Zn₂SnO₄ powders prepared at this condition was 1526 mAh/g at a current density of 0.75 mA/cm² in 0.05-3.0 V, and their irreversible capacity loss was 433 mAh/g. The discharge capacities of the Zn₂SnO₄ powders decreased with cycling and remained at 856 mAh/g after 50 cycles, which was 56% of the initial capacity.     

Synthesis of SnO2/Mg2SnO4 nanoparticles and their electrochemical performance for use in Li-ion battery electrodes

Uniform crystalline MgSn(OH)₆ nanocubes were synthesized by a hydrothermal method. The influences of reaction conditions were investigated and the results showed that the solvent constituents significantly affected the shape and size of MgSn(OH)₆·SnO₂/Mg₂SnO₄ has been obtained by thermal treatment at 850 °C for 8 h under a nitrogen atmosphere using MgSn(OH)₆ as the precursor. The electrochemical tests of SnO₂/Mg₂SnO₄ revealed that SnO₂/Mg₂SnO₄ has a higher capacity and better cyclability compared to pure SnO₂ or Mg₂SnO₄. The electrochemical performance of SnO₂/Mg₂SnO₄ was sensitive to the size of the nanoparticles. The lithium-driven structural and morphological changes of the electrode after cycling were also studied by the ex-situ XRD pattern and TEM tests. This work indicates that SnO₂/Mg₂SnO₄ is a promising anode material candidate for application in Li-ion batteries.     

Synthesis and physical characteristics of ZnAl2O4 nanocrystalline and ZnAl2O4/Eu core-shell structure via hydrothermal route

Nanocrystalline zinc aluminate (ZnAl₂O₄) particles with a spinel structure were prepared by hydrolyzing a mixture of aluminum chloride hexahydrate and zinc chloride in deionized water. It was found that pH value and reaction temperature play critical roles in the formation of nano-sized ZnAl₂O₄. Depending on pH values in the precursor solution, ZnAl layered double hydroxide (ZnAl-LDH), ZnO, boehmite or gibbsite could be formed. At pH 7 and T>120 °C, the nanocrystalline ZnAl₂O₄ particles with average particle size of ∼5 nm are easily synthesized through ZnAl layered double hydroxide (ZnAl-LDH). After surface treatment with R-OH by using the cationic surfactant CTAB, the ZnAl₂O₄/Eu core-shell structure can be developed. The ZnAl₂O₄/Eu core-shell structure can show both emissions from ⁵D₀ to ⁷F₂ sensitivity energy level and ⁵D₂ to ⁷F₀ depth energy level.     

Improving the efficiency of dye-sensitized Zn2SnO4 solar cells: The role of Al ions

The dye-sensitized Zn₂SnO₄ solar cells were treated with Al³⁺ ions to enhance the power conversion efficiency for the first time. Usually, the surface treatment on photoanodes with Al³⁺ ions generated an overlayer of Al₂O₃. For Zn₂SnO₄ photoanode, another reaction pathway was found. The treatment with Al³⁺ ions led to decreasing open circuit voltage, and a 22.6% enhancement of efficiency. Mott–Schottky measurements revealed that the flat band of Zn₂SnO₄ had a positive shift owing to the introduction of Al³⁺ ions. XPS confirmed that Al³⁺ ions were introduced into the lattice of Zn₂SnO₄ and occupied the position of Sn⁴⁺, resulting in decreased conduction band edge. TEM demonstrated the size of Zn₂SnO₄ nanoparticles became larger due to the reaction of Al³⁺ with Zn₂SnO₄. Although the adsorption amounts of dyes lowered by 21%, the driving force for electron injection was greatly enhanced as a result of decreased conduction band edge, resulting in significantly enhanced cell efficiency.     

Photoactivity of ternary lead-group IVB oxides for hydrogen and oxygen evolution

The relative photocatalytic activity of a series of lead-IVB group oxides (PbCrO₄, PbMoO₄, and PbWO₄) was studied for hydrogen evolution from aqueous methanol solution and for oxygen evolution from aqueous silver nitrate solution. Among the compounds, only PbMoO₄ and platinized PbMoO₄ powders acted as photocatalysts for oxygen and hydrogen evolution reactions from aqueous solutions, with an activity for oxygen evolution on PbMoO₄ comparable to that observed on TiO₂.     

Co-precipitated ZnAl2O4 spinel precursor as potential sintering aid for pure alumina system

Ultra-fine ZnAl₂O₄ spinel hydrogel precursor synthesized from mixed salt solutions of Zn²⁺ and Al³⁺ ions using ammonium hydroxide–hexamethylenetetramine as basic media for co-precipitation was used as bonding material and sintering aid for pure alumina system. The hydrogel powder exhibited some well-defined ZnAl₂O₄ spinel phases at 800 °C. Alumina compacts were fabricated by incorporating small proportions of the precursor in alumina powder and firing at different temperatures (1350–1500 °C). The degree of densification was studied by measurement of fired shrinkage, apparent porosity, bulk density and cold crushing strength. Phase compositions and microstructural features of sintered samples were evaluated by XRD and SEM respectively. Addition of 0.2% hydrogel powder to alumina exhibited remarkable influence on development of high mechanical strength. The in situ formed ZnAl₂O₄ spinel dopant acted as a grain growth inhibitor in the alumina system.     

Preparation and electrochemical performance of composite oxide of alpha manganese dioxide and Li-Mn-O spinel

Nano-sized composite powder which consisted of two manganese-based oxides, alpha manganese dioxide (α-MnO₂) and spinel Li-Mn-O, was successfully formed by intergrowth of the spinel phase inside α-MnO₂. This composite oxide was synthesized by precipitation and heat treatment in air; α-manganese dioxide powder was firstly prepared by oxidative precipitation of Mn(II) with K₂S₂O₈ in an aqueous solution, and then a mixture of the obtained manganese oxide powder and LiOH methanol solution was heat-treated in air. Electron microscopy and diffraction observations confirmed that the manganese oxide composite consisted of nano-sized grains of the spinel LiMn₂O₄ and α-MnO₂ phases. It was found that this α-MnO₂/spinel LiMn₂O₄ composite electrode exhibited highly reversible lithium insertion compared to the pristine α-MnO₂ and conventional LiMn₂O₄, that is, the composite demonstrated high discharge capacity of 148 mAh g⁻¹ as a cathode material of lithium cells in the potential range of 2.5-4.3 V with no significant capacity fading. It was thought that the intimately mixing of two oxides on a nanometer scale helped to maintain structural integrity on charge-discharge cycling, which leads to excellent capacity retention for both of the spinel and alpha-type manganese oxide.     

Synthesis of spherical spinel LiMn2O4 with commercial manganese carbonate

Spherical spinel LiMn₂O₄ particles were successfully synthesized from a mixture of manganese compounds containing commercial manganese carbonate by sintering of the spray-dried precursor. Different preparation routes were investigated to improve the tap density and to enhance the electrochemical performance of LiMn₂O₄. The structure and morphology of the LiMn₂O₄ particles were confirmed by X-ray diffraction (XRD) and scanning electron microscopy. The results showed that hollow spherical LiMn₂O₄ particles could be obtained when only commercial MnCO₃ was used as the manganese source. These particles had a low tap density (ca.0.8 g/cm³). Perfect micron-sized spherical LiMn₂O₄ particles with good electrochemical performance were obtained by spray-drying a slurry composed of MnCO₃, Mn(CH₃CHOO)₂ and LiOH, followed by a dynamic sintering process and a stationary sintering process. The as-prepared spherical LiMn₂O₄ particles comprised hundreds of nanosize crystal grains and had a high tap density(ca. 1.4 g/cm³). The galvanostatic charge-discharge measurements indicated that the spherical LiMn₂O₄ particles had an initial capacity of 121 mAh/g between 3.0 and 4.2 V at 0.2 C rate and still delivered a reversible capacity of 112 mAh/g at 2 C rate. The retention of capacity after 50 cycles was still 96% of its initial capacity at 0.2 C. All the results showed that the as-prepared spherical LiMn₂O₄ particles had an excellent electrochemical performances. The methods we used for preparing spherical LiMn₂O₄ are energy-saving and suitable for industrial application.     

Synthesis of spinel LiMn2O4 with manganese carbonate prepared by micro-emulsion method

Micro-spherical particle of MnCO₃ has been successfully synthesized in CTAB-C₈H₁₈-C₄H₉OH-H₂O micro-emulsion system. Mn₂O₃ decomposed from the MnCO₃ is mixed with Li₂CO₃ and sintered at 800 °C for 12 h, and the pure spinel LiMn₂O₄ in sub-micrometer size is obtained. The LiMn₂O₄ has initial discharge specific capacity of 124 mAh g⁻¹ at discharge current of 120 mA g⁻¹ between 3 and 4.2 V, and retains 118 mAh g⁻¹ after 110 cycles. High-rate capability test shows that even at a current density of 16 C, capacity about 103 mAh g⁻¹ is delivered, whose power is 57 times of that at 0.2 C. The capacity loss rate at 55 °C is 0.27% per cycle.     

Synthesis of mesoporous nanocrystalline MgAl2O4 spinel via surfactant assisted precipitation route

In this research, mesoporous nanocrystalline MgAl₂O₄ spinel powders were synthesized with a facile synthesis method by co-precipitation route using CTAB as surfactant. The prepared samples were characterized by X-ray diffraction, N₂ adsorption, thermal gravimetric and differential thermal analyses, Fourier transform infrared spectroscopy and transmission electron microscope. The effects of surfactant to metal molar ratio on the structural properties of the samples were investigated. The obtained results showed that the sample prepared without addition of surfactant presented a lower specific surface area and bigger crystallite size compared with those obtained for the samples prepared by CTAB/metal molar ratio of 0.3. The results showed that the sample prepared by CTAB/metal molar ratio of 0.3 has the highest specific surface area and the smallest crystallite size. Moreover, the CTAB/metal molar ratio higher than 0.3 led to a decrease in the specific surface area, due to destruction of the pore walls.     

Photocatalytic degradation of toluene over doped and coupled (Ti,M)O2 (M = Sn or Zr) nanocrystalline oxides: Influence of the heteroatom distribution on deactivation

In this work, we have studied the photocatalytic oxidation (PCO) of toluene over Sn- and Zr-doped TiO₂, and coupled TiO₂/SnO₂ and TiO₂/ZrO₂ catalysts. The TiO₂ sample doped with Sn (8% of metal ions) is composed by the anatase and rutile phases of TiO₂, while the Zr-doped sample (same dopant content) contains only the anatase phase. The coupled photocatalysts are formed, in addition to the phases present in their doped counterparts, by a segregated MO₂ phase (M: Sn or Zr). For the photocatalytic degradation of toluene, higher rates in the stationary state are obtained with the coupled catalysts with respect to the doped ones and the TiO₂ references (both synthetic and Degussa P25). In the case of the coupled photocatalysts, these higher rates are due to the absence of the deactivation that does occur for the rest of samples. Fresh and used photocatalysts have been studied by FTIR and EPR spectroscopies and by solid/liquid extraction in methanol, followed by GC/MS analysis. The obtained results lead us to conclude that, while structural and electronic modifications, due to the guest cations, are responsible for the high activity of doped samples observed in previous studies for a reaction not causing catalyst deactivation (methylcyclohexane PCO), other factors are crucial for the PCO of toluene. For this reaction, there is a relationship between surface water, adsorbed intermediates and resistance to deactivation, and thus the modifications in the amount and arrangement of surface water molecules caused by the second oxide may be the cause of the high degradation rate obtained with the coupled TiO₂/SnO₂ and TiO₂/ZrO₂ photocatalysts.     

Molecular dynamics studies of ZnAl2O4 spinel

Molecular dynamics simulations of ZnAl₂O₄ spinel have been carried out at 300 and 800 K. Comparison with experimental data shows that at low temperature the most favorable configuration is that of a mixed spinel. As temperature increases the structural transformation becomes more evident. A detailed interpretation of the experimental vibrational spectrum and radial distribution functions is obtained.     

Determination of the photocatalytic efficiency of TiO2 coatings on ceramic tiles by monitoring the photodegradation of organic dyes

A method for the evaluation of the photocatalytic effectiveness of nanotitania coatings on ceramic substrate was established. Decolourization of three organic dyes, including methylene blue (MB), rhodamine B (RB) and crystal violet (CV), was investigated under different experimental conditions. The results showed that the UV light spectrum and light intensity are important parameters when establishing this method.The effect of TiO₂ on the percentage degradation of the dyes was examined by varying its concentration in the suspensions between 0.1% and 4.5 wt%, which resulted in different thicknesses of the TiO₂ layers, and as expected higher percentages of nanotitania resulted in higher photocatalytic efficiencies. However higher amounts of titania lead to the formation of cracks on the surface, which might detrimentally affect adhesion and thus also long-term durability. The applicability of all the dyes used in the present study was proved, and there is good correlation between MB, RB and CV in the evaluation of self-cleaning efficiency.     

Effect of TiO2 on phase evolution and microstructure of MgAl2O4 spinel in different atmospheres

The effect of TiO₂ on the formation and microstructure of magnesium aluminate spinel (MgAl₂O₄) at 1600 °C in air and reducing conditions were investigated. Under reducing conditions, stoichiometric MgAl₂O₄ spinel shifted toward alumina-rich types owing to volatilization of MgO, resulting in an increase in the porosity of fired samples. Addition of graphite to mixtures of MgO and Al₂O₃ intensified the reducing conditions and accelerated the formation of non-stoichiometric MgAl₂O₄. For TiO₂-containing samples on addition of MgAl₂O₄, magnesium aluminum titanium oxide (Mg_xAl_2(1−x)Ti_(1+x)O₅, x = 0.2 or 0.3) was detected as a minor phase. Under reducing conditions, XRD peak shifts were smaller for TiO₂-containing samples than for samples without TiO₂ owing to the formation of a solid solution of TiO₂ in MgAl₂O₄ and establishment of alumina-rich spinel, which have opposite effects on increasing the lattice parameter. In bauxite-containing samples, MgAl₂O₄ spinel, corundum, magnesium orthotitanate spinel (Mg₂TiO₄) and amorphous phases were identified. Mg₂TiO₄ spinel formed a complete solid solution with MgAl₂O₄ spinel but Mg₂TiO₄ remained as a distinct phase owing to the heterogeneous microstructure of bauxite-containing samples. Also dense microstructure established in air fired TiO₂ containing samples. The results are discussed with emphasis on the application and design of alumina-magnesia-carbon refractory materials, which are used in the steel industry.     

Synthesis and study on phase diagram of 1-10 mol% SnO2-doped Bi2O3

Bi₂O₃ materials doped with various SnO₂ concentrations were prepared by colloidal process and solid state reactions to achieve high density and uniform microstructure. Thermal behavior, and crystalline phases of the SnO₂-doped Bi₂O₃ (BSO) samples were investigated by differential thermal analyses, X-ray diffraction, and scanning electron microscopy. A new phase diagram of Bi₂O₃-(1-10 mol%) SnO₂ system is proposed in this study. The results show that 1 mol% SnO₂ doped concentration is totally dissolved in Bi₂O₃ without the existence of any impurity phases as compared to higher doping SnO₂ concentration.     

Synthesis and electrochemical performance of LiNi0.5Mn1.5O4 spinel compound

Spinel compound LiNi_0.5Mn_1.5O₄ was synthesized by a chemical wet method. Mn(NO₃)₂, Ni(NO₃)₂·6H₂O, NH₄HCO₃ and LiOH·H₂O were used as the starting materials. At first, Mn(NO₃)₂ and Ni(NO₃)₂·6H₂O reacted with NH₄HCO₃ to produce a precursor, then the precursor reacted with LiOH·H₂O to synthesize product LiNi_0.5Mn_1.5O₄. The product showed a single spinel phase under appropriate calcination conditions, and exhibited a high voltage plateau at about 4.6-4.8 V in the charge/discharge process. The LiNi_0.5Mn_1.5O₄ had a discharge specific capacity of 118 mAh/g at about 4.6 V and 126 mAh/g in total in the first cycle at a discharge current density of 2 mA/cm². After 50 cycles, the total discharge capacity was above 118 mAh/g.     

Synthesis,Magnetic Anisotropy and Optical Properties of Preferred Oriented Zinc Ferrite Nanowire Arrays

Preferred oriented ZnFe₂O₄ nanowire arrays with an average diameter of 16 nm were fabricated by post-annealing of ZnFe₂ nanowires within anodic aluminum oxide templates in atmosphere. Selected area electron diffraction and X-ray diffraction exhibit that the nanowires are in cubic spinel-type structure with a [110] preferred crystallite orientation. Magnetic measurement indicates that the as-prepared ZnFe₂O₄ nanowire arrays reveal uniaxial magnetic anisotropy, and the easy magnetization direction is parallel to the axis of nanowire. The optical properties show the ZnFe₂O₄ nanowire arrays give out 370–520 nm blue-violet light, and their UV absorption edge is around 700 nm. The estimated values of direct and indirect band gaps for the nanowires are 2.23 and 1.73 eV, respectively.     

Synthesis and magnetic properties of nanoporous Co3O4 nanoflowers

Nanoporous Co₃O₄ hierarchical nanoflowers have been prepared through sequential process of a hydrothermal reaction and heat treatment. These nanoflowers consisting of a great deal of Co₃O₄ nanofibers have bimodal pore structures and Brunauer–Emmett–Teller surface area of 34.61 m²/g. The temperature dependence curves of magnetization in zero-field-cooled and field-cooled exhibit main antiferromagnet and weak ferromagnet of Co₃O₄ nanoflowers at blocking temperature of 34 K, respectively. In addition, analysis of their optic properties obviously indicates red shift of absorption peaks, exhibiting quantum-confined effect and traits of semiconductor.     

Facile method to synthesize magnetic iron oxides/TiO2 hybrid nanoparticles and their photodegradation application of methylene blue

The primary objective of this study is to investigate the effect of slip mechanisms in nanofluids through scaling analysis. The role of nanoparticle slip mechanisms in both water- and ethylene glycol-based nanofluids is analyzed by considering shape, size, concentration, and temperature of the nanoparticles. From the scaling analysis, it is found that all of the slip mechanisms are dominant in particles of cylindrical shape as compared to that of spherical and sheet particles. The magnitudes of slip mechanisms are found to be higher for particles of size between 10 and 80 nm. The Brownian force is found to dominate in smaller particles below 10 nm and also at smaller volume fraction. However, the drag force is found to dominate in smaller particles below 10 nm and at higher volume fraction. The effect of thermophoresis and Magnus forces is found to increase with the particle size and concentration. In terms of time scales, the Brownian and gravity forces act considerably over a longer duration than the other forces. For copper-water-based nanofluid, the effective contribution of slip mechanisms leads to a heat transfer augmentation which is approximately 36% over that of the base fluid. The drag and gravity forces tend to reduce the Nusselt number of the nanofluid while the other forces tend to enhance it.     

Synthesis of highly crystalline spinel LiMn2O4 by a soft chemical route and its electrochemical performance

Highly crystalline spinel LiMn₂O₄ was successfully synthesized by annealing lithiated MnO₂ at a relative low temperature of 600 °C, in which the lithiated MnO₂ was prepared by chemical lithiation of the electrolytic manganese dioxide (EMD) and LiI. The LiI/MnO₂ ratio and the annealing temperature were optimized to obtain the pure phase LiMn₂O₄. With the LiI/MnO₂ molar ratio of 0.75, and annealing temperature of 600 °C, the resulting compounds showed a high initial discharge capacity of 127 mAh g⁻¹ at a current rate of 40 mAh g⁻¹. Moreover, it exhibited excellent cycling and high rate capability, maintaining 90% of its initial capacity after 100 charge-discharge cycles, at a discharge rate of 5 C, it kept more than 85% of the reversible capacity compared with that of 0.1 C.