Showing papers by "Huijun Ren published in 2014"

Photoelectric Activity of a Bi2O3/Bi2WO6–xF2x Heterojunction Prepared by a Simple One-Step Microwave Hydrothermal Method

Abstract: NH4F/Bi2WO6 powders were prepared by a simple one-step microwave hydrothermal method at different reaction temperatures, using Bi(NO3)3·5H2O and Na2WO4·2H2O as raw materials and NH4F as an additive agent. Their photoelectric activities were also investigated via the degradation of Rhodamine B (RhB). The results indicate that when the reaction temperature increases to 220 and 240 °C, the orthorhombic Bi2WO6 phase with space group Pca21 and cubic Bi2O3 phase with space group Pn3m appear. Raman spectroscopy, SEM, TEM, and XPS results also confirm the existence of a Bi2O3/Bi2WO6–xF2x heterojunction at higher temperature. Greater than 95% photodegradation of RhB under the exposure of simulated sunlight is achieved within 90 min with the Bi2O3/Bi2WO6–xF2x heterojunction prepared at 220 °C, which displays remarkably promoted photocatalytic activities. The electrochemical impedance spectra and photocurrent results also prove that efficient charge separation and better electron transport properties are achieved b...

Structure transition and multiferroic properties of Mn-doped BiFeO 3 thin films

Abstract: Pure BiFeO3 (BFO) and Mn-doped BiFe1−yMnyO3 thin films were prepared on FTO/glass (SnO2: F) substrates by using a sol–gel method. The effects of Mn-doping on the structure and electric properties of the BFO thin films were studied. The X-ray diffraction (XRD) analysis reveals a structure transition in the Mn-doped BiFe0.96Mn0.04O3 (BFMO) thin film. The Rietveld refined XRD patterns conform the trigonal (R3c: H) and tetragonal (P422) symmetry for the BFO and BFMO thin films, respectively. The structure transition and the mixed valences of Mn ions substantially improve the electric properties of the BFMO thin film. The remnant polarization (P r) of the BFMO thin film was 105.86 μC/cm2 at 1 kHz in the applied electric field of 865 kV/cm. At an applied electric field of 150 kV/cm, the leakage current density of BFMO thin film is 1.42 × 10−5 A/cm2. It is about two orders of magnitude lower than that of the pure BFO thin film (1.25 × 10−3 A/cm2). And the enhanced saturated magnetization of the BFMO thin film is 4.45 emu/cm3.

Two-Phase Coexistence and Multiferroic Properties of Cr-Doped BiFeO3 Thin Films

Abstract: Pure BiFeO 3 (BFO) and Cr-doped BiFe 0.97 Cr 0.03 O 3 (BFCO) thin films were successfully prepared on F-doped SnO 2 conductive film (FTO)/glass (SnO 2: F) substrates by a sol–gel method. The effect of Cr doping on the structure, ferroelectric, and ferromagnetic properties of the BFO and BFCO thin films have been investigated. X-ray diffraction, Rietveld refined X-ray diffraction (XRD) patterns, and Raman spectroscopy results clearly reveal that the BFCO thin film is characterized by the coexistence of two phases (trigonal and tetragonal). Moreover, the various leakage mechanisms of both thin films have also been studied. The improved ferroelectricity with remnant polarization (Pr) of about 2Pr = 68.68 μC/cm 2 under an applied electric field of 1,181.8 kV/cm and enhanced ferromagnetism with saturation magnetization (M s) of M s = 0.93 emu/cm 3 have been observed in the BFCO thin film. The improved electrical properties of the BFCO thin film are ascribed to the coexistence of trigonal and tetragonal phase and high valence of Cr 6+, and the Fe–O 6 octahedron distortion is enhanced due to the overlap and hybridization of Fe 3d/Cr 3d and O 2p orbits by Cr doping.

Phase transition and piezoelectric properties of (1 − x)K0.5Na0.5NbO3–xLiSbO3 ceramics by hydrothermal powders

Abstract: KNbO3, NaNbO3 and LiSbO3 powders were synthesized by a hydrothermal route have been used to prepare (1 − x)K0.5Na0.5NbO3–xLiSbO3 (KNN–LS; x = 0.00–0.08) ceramics. The effects of LiSbO3 doping on the structures of KNN–LS ceramics have been systematically investigated by X-ray diffraction (XRD) and Rietveld refined XRD patterns. A gradual phase transition from orthogonal to tetragonal with the increase of LiSbO3 content is demonstrated. Thereinto, the monoclinic phase is identified for the KNN–LS ceramic with the LiSbO3 content of x = 0.08. Meanwhile, the XRD pattern reveals that the intensity ratio of (200)/(002) crystal face of the ceramic with x = 0.08 was bigger than one, which is different from the tetragonal phase. The tetragonal phase is revealed in the KNN–LS ceramic in the vicinity of x = 0.07, accompanying with relatively higher piezoelectric and ferroelectric properties. Tetragonal phase is beneficial to improve the piezoelectric properties of the KNN–LS ceramics.

Multi-factors on photocatalytic properties of Y-doped Bi2WO6 crystallites prepared by microwave-hydrothermal method

Abstract: Different contents of Y-doped Bi2WO6 crystallites were synthesized by a microwave-hydrothermal method. The photocatalytic properties with different contents of Y-doped Bi2WO6 crystallites were studied. The Y-doped Bi2WO6 crystallites were also characterized by XRD, EDX, SEM and UV-vis DRS and the multi-factors on photocatalytic properties of Y-Doped Bi2WO6 crystallites were discussed. The results indicate that Y3+ replacing Bi3+ enters into the Bi2WO6 lattice, producing a degree of Bi2WO6 lattice distortion. It also has an impact on the crystallinity of Bi2WO6 and the band gap is from 2.49 eV to 2.71 eV. The photocatalytic results show that when the content of Y doping becomes 10%, the degradation rate of rhodamine B is above 90% after 40 min irradiation, which shows that doping the proper rare earth ions is conducive to the photocatalytic properties of Bi2WO6 crystallites.

Enhanced photocatalytic of N/F-doped-NaTaO3 photocatalyst synthesized by hydrothermal method

Abstract: N/F-doped NaTaO3 powders were synthesized via a hydrothermal method at 160 °C. The influences of N/F co-doping on the crystal structure, morphology and photocatalytic properties of the NaTaO3 powders were investigated systematically. Rietveld refinement of X-ray diffraction data confirm that the nanoparticles of pure NaTaO3 have orthorhombic structures with Pc21n:bca and Ta2O5 can be obtained by doping N/F molar ratio (NaOH/NH4F ≤ 1) with the orthorhombic P2 mm:cab space group. The NaTaO3 powders are transformed from orthorhombic Pc21n:bca into monoclinic P2/m:b space group with the NaOH/NH4F molar ratio (NaOH/NH4F > 1). The well-defined cubic block NaTaO3 single-crystalline particles with the size of 0.5 μm are determined using TEM and grow preferentially along (101) and (010) crystal planes. The photocatalytic activities were evaluated by the degradation of Rhodamine B under UV-light irradiation. The possible mechanism is proposed to discuss the enhanced photocatalytic activity based on the increasing separation efficiency of photoinduced charge. The results illustrate that the obtained monoclinic N/F-NaTaO3 (NaOH/NH4F = 1.5/1.0) powder exhibits the best photocatalytic activity with the UV-light irradiation for 210 min.

Growth mechanism and photocatalytic properties of flower-like Bi2WO6 powders synthesized by a microwave hydrothermal method

Abstract: Pure orthorhombic phase Bi2WO6 powders were synthesized by a microwave hydrothermal method in the absence of surfactants and templates, using Bi(NO3)3·5H2O and Na2WO4·2H2O as raw materials. Photocatalytic properties of the samples prepared at different reaction temperatures were also studied with Rhodamine B (RhB) solution as the target catabolite under visible light. The results indicate that flower-like Bi2WO6 powders can be obtained by controlling the microwave reaction temperatures in the absence of any additives. The growth of flower-like Bi2WO6 powders is a multistage layer assembly process, in which the flower-like Bi2WO6 self-assembling with the uniform size about 2 μm is synthesized at 180 °C. At the same time, the photocatalytic reaction rate constant (k) gets up to 0.04167/min and the degradation rate of RhB solution is more than 96 % after being irradiated under visible light for 70 min.

Structure, conduction mechanisms and multiferroic properties of (Sm, Cr) co-doped Bi 0.89 Sm 0.11 Fe 0.97 Cr 0.03 O 3 –NiFe 2 O 4 composition thin films

Abstract: (Sm, Cr) co-doped Bi0.89Sm0.11Fe0.97 Cr0.03O3 (BSFC)–NiFe2O4 (NFO) composition thin films were successfully prepared on FTO/glass (SnO2:F) substrates via a sol–gel method. The structure, surface morphology, leakage current, ferroelectricity and ferromagnetism of BSFC–NFO composition thin film have been investigated. X-ray diffraction analysis indicates that the thin film is polycrystalline and consisted of a rhombohedral perovskite (R3m space group) BiFeO3 phase and a cubic (Fd-3m space group) inverse spinel NiFe2O4 phase. The BSFC–NFO composition thin film is promising in practical application because of its well saturated ferromagnetic (Ms = 19.45 emu/cm3) and ferroelectric (Pr = 39 µC/cm2) hysteresis loops with low order of leakage current density (J = 6.73 × 10−6 A/cm2, at an applied electric field of 100 kV/cm). Which suggest the ferroelectric and ferromagnetic properties can be improved by this composition thin film structure. Moreover, the various conduction mechanisms of BSFC–NFO composition thin film have also been studied.