Lihong Xue

Sol–gel combustion synthesis of nanocrystalline LaMnO3 powders and photocatalystic properties

A novel LaMnO3 photocatalyst with perovskite structure was prepared by sol–gel combustion method. The combustion reaction mechanisms of nanocrystalline LaMnO3 powders were investigated by thermal analysis, infrared spectra, and X-ray diffraction technique. The results showed that the gels exhibited self-propagating behavior after ignition in air. Nanocrystalline LaMnO3 powders can be synthesized in one step by using sol–gel combustion synthesis. The photocatalytic activity of the LaMnO3 powders were evaluated by degradation of methyl orange (MO) in water under UV light irradiation. The results showed that the LaMnO3 powders exhibit good photocatalytic activities under UV light irradiation. The degradation percentage after 36xa0h on LaMnO3 powders was about 76%.

Mechanism of Capacity Fade in Sodium Storage and the Strategies of Improvement for FeS2 Anode

Pyrite FeS2 has attracted extensive interest as anode material for sodium-ion batteries due to its high capacity, low cost, and abundant resource. However, the micron-sized FeS2 usually suffers from poor cyclability, which stems from structure collapse, exfoliation of active materials, and sulfur dissolution. Here, we use a synergistic approach to enhance the sodium storage performance of the micron-sized FeS2 through voltage control (0.5-3 V), binder choice, and graphene coating. The FeS2 electrode with the synergistic approach exhibits high specific capacity (524 mA h g-1), long cycle life (87.8% capacity retention after 800 cycles), and excellent rate capability (323 mA h g-1 at 5 A g-1). The results prove that a synergistic approach can be applied in the micron-sized sulfides to achieve high electrochemical performance.

Polypyrrole-promoted superior cyclability and rate capability of NaxFe[Fe(CN)6] cathodes for sodium-ion batteries

Sodium iron hexacyanoferrate (Fe-HCF) is a potential cathode material for sodium-ion batteries. However, the side reactions in the NaClO4 electrolyte in the charge process over 4.1 V result in structural collapse and low coulombic efficiency during cycling. In this work, we prepared high-quality Fe-HCF microcubes with a size distribution of ∼2 μm and employed conductive polypyrrole (PPy) to wrap the microcubes to form a Fe-HCF@PPy composite. With the coating of PPy, the composite exhibits a discharge capacity of 113.0 mA h g−1 at a current density of 25 mA g−1 and 75 mA h g−1 at 3000 mA g−1. A greatly improved cycling stability is attained with 79% capacity retention over 500 cycles at 200 mA g−1. The superior rate capability and excellent cyclability can be ascribed to the effects from PPy as both an electronic conductor to enhance the conductivity and a protective layer to prevent the side reactions.

Combustion synthesis and luminescent properties of a blue-green emitting phosphor: (Ba1.95, Eu0.05)ZnSi2O7:B3+

A blue-green emitting phosphor (Ba1.95, Eu0.05)ZnSi2O7: Bx3+ was prepared by combustion synthesis and an efficient blue-green emission under near-ultraviolet was observed. The luminescence, crystallinity and particle sizes were investigated by using luminescence spectrometry, X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The emission spectrum shows a single band centered at 503 nm, which corresponds to the 4f65d1 →4f7 transition of Eu2+. The excitation spectrum is a broad band extending from 260 to 465 nm, which matches the emission of ultraviolet light-emitting diodes. The optical absorption spectra of the (Ba1.95, Eu0.05)ZnSi2O7: B0.063+ exhibited band-gap energies of 3.9 eV. The results showed that boric acid was effective in improving the luminescence intensity of (Ba1.95, Eu0.05)ZnSi2O7, and the optimum molar ratio of boric acid to zinc nitrate was about 0.06. The phosphor (Ba1.95, Eu0.05)ZnSi2O7: B0.063+ synthesized by combustion method showed 1.5 times improved emission intensity compared with that of the Ba1.95ZnSi2O7: Eu0.052+ phosphor under λex = 353 nm.

Preparation of V-doped TiO2 photocatalysts by the solution combustion method and their visible light photocatalysis activities

A series of nanocrystalline V-doped (0.0–3.0 at.%) TiO2 catalysts have been successfully prepared by the one-step solution combustion method using urea as a fuel. The obtained powders were characterized by XRD, SEM, Raman, XPS and UV-Vis DRS. The effects of V doping concentration on the phase structure and photocatalytic properties were investigated. XRD, Raman, and XPS show that V doping diffuses into TiO2 crystal lattice mainly in the form of V5+ and causes a phase transition from anatase to rutile. V doping can widen the light absorption range of TiO2, with the absorption threshold wavelength shifting from 425 to 625 nm. The photocatalytic activity of V-doped TiO2 powders were evaluated by the photocatalytic degradation of methyl orange (MO) under visible light irradiation. It is found that V doping enhances the photocatalytic activity under visible light irradiation and the optimal degradation rate of MO is about 95.8% with 1.0 at% V-doped TiO2.

Ultrasonic-assisted solution combustion synthesis of porous Na3V2(PO4)3/C: formation mechanism and sodium storage performance

AbstractSolution combustion synthesis (SCS) is an effective and rapid method for synthesizing nanocrystalline materials. However, the control over size, morphology, and microstructure are rather limited in SCS. Here, we develop a novel ultrasonic-assisted solution combustion route to synthesize the porous and nano-sized Na3V2(PO4)3/C composites, and reveal the effects of ultrasound on the structural evolution of NVP/C. Due to the cavitation effects generated from ultrasonic irradiation, the ultrasonic-assisted SCS can produce honeycomb precursor, which can be further transformed into porous Na3V2(PO4)3/C with reticular and hollow structures after thermal treatment. When used as cathode material for Na-ion batteries, the porous Na3V2(PO4)3/C delivers an initial discharge capacity of 118xa0mAhxa0g−1 at 0.1 C and an initial coulombic efficiency of 85%. It can retain 93.8% of the initial capacity after 120xa0cycles at 0.2 C. The results demonstrate that ultrasonic-assisted SCS can be a new strategy to design crystalline nanomaterials with tunable microstructures.n Graphical abstractPorous and nano-sized Na3V2(PO4)3/C composites with reticular and hollow structures are synthesized by an ultrasonic-assisted solution combustion route due to the cavitation effects, and exhibit excellent electrochemical performance as cathode in sodium ion battery.

Hydrothermal synthesis of bismuth sodium titanate particles with different morphologies

Nanostructured Na0.5Bi0.5TiO3 particles have been synthesized by a hydrothermal synthesis method using a layered titanate H1.07Ti1.73O4·nH2O as a Ti precursor. The obtained Na0.5Bi0.5TiO3 particles showed different morphologies including plate-like, wire-like, and cubic-like structures in different hydrothermal conditions. The effect of the NaOH concentration on the growth and morphology evolution of hydrothermally derived Na0.5Bi0.5TiO3 powders were investigated. It was found that alkaline concentration had a great effect on the phase and morphology of the resultant powders. The dissolution–recrystallization and in situ topotactic transformation mechanisms were suggested in different alkaline concentrations according to the evolution process.

Effects of reaction parameters on solution combustion synthesis of lepidocrocite-like K0.80Ti1.733Li0.267O4: phase formation and morphology evolution

A lepidocrocite-like potassium lithium titanate K0.80Ti1.733Li0.267O4 (KLTO) with layered structure was synthesized by an auto-igniting solution combustion method using glycine and metal (Ti, K and Li) nitrate as reactants. The crystalline structure and morphology of the as-prepared product were examined using X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy. Effects of reaction parameters such as ignition temperature and oxidizers to fuel ratio on the phase formation and morphology evolution are investigated in this paper. A pure phase of KTLO was obtained at a low temperature (650xa0°C) within several minutes. Excessive glycine added into the aqueous precursor solution facilitated the synthesis of a pure and well-crystallized product. As-prepared particles exhibited plate-like shape with a length of 5–20xa0μm and a thickness of about 2xa0μm. No residual organic compound existed in the product. After the as-prepared product was post solution combustion heat-treated (1100xa0°C for 2xa0h), the particles became uniform in size with smooth surface and well-defined crystalline structure. The product exhibited excellent ion-exchange, intercalation, and exfoliation properties. The exfoliated titania nanosheets are characterized by high two-dimensional anisotropy with a thickness of about 20xa0nm and a lateral size ranging from sub-micrometers to several tens of micrometers.

Luminescence studies on Ba2ZnSi2O7 : Eu2+ phosphors crystals

A novel blue green-emitting phosphor, Ba₂ZnSi₂O₇:u2009Eu(2+), was prepared by combustion synthesis method and an efficient bluish green emission under from ultraviolet to visible light was observed. The emission spectrum shows a single intensive band centered at 503u2009nm, which corresponds to the 4f(6)5d(1) → 4f(7) transition of Eu(2+). The excitation spectrum is a broad band extending from 260 to 465u2009nm, which matches the emission of ultraviolet light-emitting diodes (UV-LEDs). The effect of doped Eu(2+) concentration on the emission intensity of Ba₂ZnSi₂O₇:u2009Eu(2+) was also investigated. The result indicates that Ba₂ZnSi₂O₇:u2009Eu(2+) can be potentially useful as a UV radiation-converting phosphor for white light-emitting diodes.

Graphene-induced growth of single crystalline Sb2MoO6 sheets and their sodium storage performance

A single crystalline molybdenum antimony oxide (Sb2MoO6) sheet/reduced graphene oxide (RGO) composite is reported for the first time, for use as an anode for a sodium ion battery with excellent cyclability and rate performance. The addition of graphene oxides in the hydrothermal synthesis can not only induce the tabular growth of Sb2MoO6 single crystals but also serves as a conductive network in the electrochemical reactions. The Sb2MoO6/RGO composite exhibits a capacity of 430 mA h g−1 at 0.05 A g−1 and maintains 270 mA h g−1 at a high current density of 4 A g−1. A capacity retention of 93.2% can be acquired after 220 cycles at 0.2 A g−1. In situ X-ray diffraction, ex situ transmission electron microscopy and X-ray photoelectron spectroscopy reveal a conversion reaction in the initial cycle of the Sb2MoO6/RGO composite. Thus, the reversible capacity is mainly imparted by the alloying/dealloying reactions of the antimony element, while amorphous molybdenum oxide (MoOx) and sodium oxide (Na2O) composites serve as the buffer matrix.