Yun-fei Liu

Nanjing University of Technology, Nan-ching, Jiangsu Sheng, China

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Publications (7)18.39 Total impact

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    ABSTRACT: BaMoO(4) with 3D hierarchical multilayer disk-like and nest-like architectures self-assembled from 2D nanosheets was successfully synthesized via a microwave-assisted hydrothermal route without any surfactant. The as-prepared products were characterized by X-ray powder diffractometer (XRD), scanning electron microscope (SEM), field emission transmission electron microscope (FE-TEM), and photoluminescence (PL) spectrometer. The results show that the reaction parameters, including pH value, reactant concentration, and molar ratio of [Ba(2+)]/[MoO(4)(2-)], played important roles on the morphologies of the final products. And the formation mechanism of 3D hierarchical architectures is a stepwise oriented aggregation-based self-assembly process. The superstructure characteristic of 3D nest-like BaMoO(4) architecture was observed in HRTEM image and the corresponding fast Fourier transform (FFT) for the first time, and the superlattice reflections with non-integer indices occurred around the subcell reflections at ±1/6(2a*+2c*). Room temperature photoluminescence spectra of 3D BaMoO(4) architectures reveal a strong and broad blue emission, and the 3D nest-like architectures own the enhanced intensity than multilayer disks.
    No preview · Article · May 2012 · Journal of Colloid and Interface Science
  • Yun-Fei Liu · Shen-Hua Dai · Yi-Nong Lu · Hui-Hua Min
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    ABSTRACT: Uniform SrMoO4 micro-octahedrons were synthesized by microwave heating method. The as-prepared products were characterized by several techniques. Results showed that the reactant concentration and reaction time had crucial influence on the morphology of the products. The possible growth process of SrMoO4 octahedron was proposed based on the time-dependent shape evolution, which followed Ostwald ripening, crystallization/dissolution, and re-crystallization. Eu3 +-doped (1–20 mol%) SrMoO4 with octahedrons-like polyhedron was prepared under the same condition. The excitation spectrum of SrMoO4:Eu3 + was mainly composed of three intense peaks of 305, 393 and 463 nm. The characteristic red emission peaks at 612/615 nm were ascribed to 5D0 → 7F2 transition of Eu3 + ions. The quenching concentration was found at ~ 15 mol% doping of Eu3 +.
    No preview · Article · May 2012 · Powder Technology
  • Shen-Hua Dai · Yun-Fei Liu · Yi-Nong Lu
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    ABSTRACT: In this study, (Y,Gd)(2)O(3) and (Y,Gd)(2)O(3):Eu flowerlike microstructures were prepared through two steps: well-organized 3-dimensional (3D) flowerlike precursors were first synthesized by a facile urea-based microwave hydrothermal method, then followed by heat treatment. The morphology of the 3D flowerlike precursors could be modulated by adjusting the synthetic conditions including concentration of the starting material, reaction time and temperature. Higher the concentration of Y/Gd ions or reaction temperature, earlier the 3D flowerlike precursors were obtained. The samples were characterized by various means. The flowers were found to derive from colloidal spheres, which experienced a dissolution/crystalline, attachment and self-assembly process. Room temperature photoluminescence spectrum of 3D flowerlike (Y,Gd)(2)O(3):Eu showed enhanced emission property than the spheres.
    No preview · Article · Sep 2010 · Journal of Colloid and Interface Science
  • Shen-Hua Dai · Yun-Fei Liu · Yi-Nong Lu · Hui-Hua Min
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    ABSTRACT: A microwave-assisted solvothermal process was employed to synthesize the sheet-like (Y,Gd)-oxalate precursors. (Y,Gd)2O3 was obtained by thermal decomposition of the precursors above 550°C. The samples were analyzed by X-ray diffraction (XRD), Fourier-transform infrared spectrometry (FT-IR), scanning electron microscopy (SEM), thermogravimetric/differential scanning calorimeters (TG/DSC), and transmission electron microscopy (TEM). It was found that the sheet-like (Y,Gd)-oxalate precursors (indicated as (Y,Gd)2(C2O4)3·nH2O) were sensitive to the synthetic conditions such as microwave irradiation power and volume ratio of ethylene glycol (EG) to water (defined as R). When R=1, the products presented sheet-like morphology, and higher R value could change the aspect ratio of precursor to micro/nano rod-like. The possible growth process was also proposed based on the results. The excitation spectrum of the (Y,Gd)2O3:Eu3+ (5mol% of Eu3+) microsheets was observed with a maximum peak at 238nm (λem=611nm). The emission spectrum was recorded under excitation wavelength of 238nm and exhibited the strongest peak at 611nm. In addition, (Y,Gd)2O3:Eu3+ with sheet-like shape had the strongest emission peaks.
    No preview · Article · Aug 2010 · Powder Technology
  • Yun-fei Liu · Yi-nong Lu · Shen-hua Dai · Shu-zhe Shi
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    ABSTRACT: Tetragonal perovskite structure PbTiO3 donut-like particles have been synthesized by a hydrothermal method in strong alkaline environment using lead nitrate (Pb(NO3)2) as the lead source and TiCl4 as the titanium source. The as-prepared particles were characterized by X-ray powder diffraction (XRD) and scanning electron microscope (SEM), and it was indicated that the phase composition and particles shapes were influenced by the reaction temperature and reaction time. Based on the morphologies and phase evolutions as a function of reaction temperature or reaction time, a mechanism for the growth of the donut-like PbTiO3 particles was proposed to involve nucleation, agglomeration, phase in situ conversion, dissolution, and recrystallization. The spherical particles were formed by primary nucleation of PbTi0.8O2.6 followed by agglomeration into platelets. Then, the platelet PbTi0.8O2.6 particles in situ converted into Pb2Ti2O6 particles. Under the effects of temperature, pressure (autogenous pressure), and high solution pH value, the platelet Pb2Ti2O6 particles dissolved from its center of surface and recrystallized to form PbTiO3 nano-particles which adhered to its edges. Finally, the monocrystal donut-like PbTiO3 particles were formed as the dissolution of Pb2Ti2O6 particles completed.
    No preview · Article · Feb 2010 · Powder Technology
  • Yun-fei Liu · Yi-nong Lu · Ming Xu · Liu-fei Zhou · Shu-zhe Shi
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    ABSTRACT: Molten salt synthesis (MSS) is an effective method to prepare anisotropic shaped single crystals. In this study strontium titanate (SrTiO3) (ST) platelet crystals were successfully synthesized based on Sr3Ti2O7 (S3T2) platelet precursor in MSS process. The objective is to identify the formation mechanism of SrTiO3 platelet crystals based on Sr3Ti2O7 platelet precursor. During the synthesis process of Sr3Ti2O7 and SrTiO3 crystals, the final sizes are strongly influenced by the sorts of alkali chloride medium. Sr3Ti2O7 and SrTiO3 crystals with 30–50 μm in edge length and ∼2 μm in thickness are obtained in KCl medium. The conversion of SrTiO3 platelet crystals from Sr3Ti2O7 platelet precursor is a topochemical process, including diffusion of Sr and O atoms, and reconstruction of SrTiO3 blocks. In the topochemical process, TiO2 is the driving force of diffusion of Sr and O atoms from SrO layer in Sr3Ti2O7, which reacts with dissociative Sr2+ and O2− to form SrTiO3 in different positions: deposited at interior pores and surface of Sr3Ti2O7, and dispersed in molten salt medium.
    No preview · Article · Mar 2009 · Materials Chemistry and Physics
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    ABSTRACT: Monosized spherical particles of BaTiO3 have been successfully synthesized by a sonochemical method in a strong alkaline environment using BaCl2·2H2O as the barium source and TiCl4 as the titanium source. The as-prepared BaTiO3 powders were characterized by employing techniques including X-ray powder diffraction (XRD), scanning electron microscope (SEM), energy dispersive analysis of X-rays (EDAX) and laser particle size analyzer. The effects of reactant concentrations and Ba/Ti molar ratio on the precipitation of BaTiO3 particles were briefly investigated. The particles have a monosized spherical morphology and the particle size ranges from submicron (600–800 nm) to nanometer (60–70 nm) by increasing the reactant concentration (from 0.072 mol/L to 0.72 mol/L). The studies indicated that increasing the Ba/Ti ratio can promote synthesis of BaTiO3.
    No preview · Article · Feb 2006 · Powder Technology