Longwei Yin

Shandong University, Chi-nan-shih, Shandong Sheng, China

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Publications (24)71.79 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: To improve the electrochemical performance of spinel ZnMn2O4, i.e., its limited specific capacity, cycling performance, and rate properties, owing to its inherent poor electrical conductivity and large volume changes during lithiation and delithiation processes, spinel ZnMn2O4 nanocrystals are anchored into a three dimensional (3D) porous carbon aerogel (CA) through a facile solution immersion chemical route. The designed 3D spinel ZnMn2O4/CA hybrids display the advantages of both spinel ZnMn2O4 and porous CA: enormous interfacial surface area, connected 3D framework, abundant porosity and high electron transport properties of CA, and electrochemical properties of nanostructured spinel ZnMn2O4 oxide materials. The synthesized novel ZnMn2O4/CA hybrids display a significantly improved electrochemical performance, with a high reversible specific capacity, and high-rate capability, as well as an excellent cycling performance, superior to that of previously reported ZnMn2O4-based materials. After 50 cycles, the 50%ZnMn2O4/CA hybrid displays a reversible capacity of 833 mAh g−1 at a current density of 100 mAg-1, much higher than the theoretical capacity of 784 mAh g−1 for pure spinel ZnMn2O4 materials, corresponding to a Coulombic efficiency of 99.9%. The greatly improved cycle stability, specific capacity, and high rate performance of the ZnMn2O4/CA hybrids can be attributed to the synergistic interaction between spinel-structured ZnMn2O4 nanoparticles and the 3D interconnected porous CA matrix.
    Advanced Functional Materials 04/2014; · 9.77 Impact Factor
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    ABSTRACT: To eliminate capacity-fading effects due to the loss of sulfur cathode materials as a result of polysulfide dissolution in lithium–sulfur (Li–S) cells, 3D carbon aerogel (CA) materials with abundant narrow micropores can be utilized as an immobilizer host for sulfur impregnation. The effects of S incorporation on microstructure, surface area, pore size distribution, and pore volume of the S/CA hybrids are studied. The electrochemical performance of the S/CA hybrids is investigated using electrochemical impedance spectroscopy, galvanostatical charge–discharge, and cyclic voltammetry techniques. The 3D porous S/CA hybrids exhibit significantly improved reversible capacity, high-rate capability, and excellent cycling performance as a cathode electrode for Li–S batteries. The S/CA hybrid with an optimal incorporating content of 27% S shows an excellent reversible capacity of 820 mAhg−1 after 50 cycles at a current density of 100 mAg−1. Even at a current density of 3.2C (5280 mAg−1), the reversible capacity of 27%S/CA hybrid can still maintain at 521 mAhg−1 after 50 cycles. This strategy for the S/CA hybrids as cathode materials to utilize the abundant micropores for sulfur immobilizers for sulfur impregnation for Li–S battery offers a new way to solve the long-term reversibility obstacle and provides guidelines for designing cathode electrode architectures.
    Advanced Functional Materials 12/2013; · 9.77 Impact Factor
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    ABSTRACT: A novel hybrid of MoO2-ordered mesoporous carbon (MoO2-OMC) was prepared through a two-step solvothermal chemical reaction route. The electrochemical performances of the mesoporous MoO2-OMC hybrids were examined using galvanostatical charge-discharge, cyclic voltammetry, and electrochemical impedance spectroscopy (EIS) techniques. The MoO2-OMC hybrid exhibits significantly improved electrochemical performance of high reversible capacity, high-rate capability, and excellent cycling performance as an anode electrode material for Li ion batteries. It is revealed that the MoO2-OMC hybrid could deliver the first discharge capacity of 1641.8 mA h g(-1) with an initial Coulombic efficiency of 63.6%, and a reversible capacity as high as 1049.1 mA h g(-1) even after 50 cycles at a current density of 100 mA g(-1), much higher than the theoretical capacity of MoO2 (838 mA h g(-1)) and OMC materials. The MoO2-OMC hybrid demonstrates an excellent high rate capability with capacity of ∼600 mA h g(-1) even at a charge current density of 1600 mA g(-1) after 50 cycles, which is approximately 11.1 times higher than that of the OMC (54 mA h g(-1)) materials. The improved rate capability and reversible capacity of the MoO2-OMC hybrid are attributed to a synergistic reaction between the MoO2 nanoparticles and mesoporous OMC matrices. It is noted that the electrochemical performance of the MoO2-OMC hybrid is evidently much better than the previous MoO2-based hybrids.
    Physical Chemistry Chemical Physics 07/2013; · 3.83 Impact Factor
  • Dong Xiang, Rui Tang, Qingcai Su, Longwei Yin
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    ABSTRACT: Hybrids of bimetallic NiFex crystalline nanoparticles homogeneously embedded in ordered mesoporous carbon (OMC) for electrochemical hydrogen storage applications were fabricated through wet impregnation and H2 reduction techniques. The size and distribution of NiFex nanoparticles of NiFex/OMC hybrids can be tuned by controlling the molar ratio of Ni:Fe, with the smallest diameter of 4.7 nm for the NiFe2 alloy nanoparticles. The effects of NiFex nanoparticle incorporation into the OMC matrix on the surface area, pore volume, pore size and electrochemical hydrogen storage performances were comparatively investigated using adsorption isotherms of nitrogen, electrochemical impedance spectroscopy, potentiodynamic polarization, cyclic voltammetry and galvanostatic charge–discharge techniques. With the molar ratio of Ni:Fe decreasing, the discharge capacity and the cycle performance of the NiFex/OMC hybrids display a notable improvement due to the homogenous dispersion of NiFex nanoparticles, higher surface area, larger mesopore volume, lower defect ration, and smaller charge-transfer resistance. The NiFe2/OMC samples display greatly improved electrochemical hydrogen storage discharge capacity of 418 mA h g−1, which is about four times as high as that of the pure OMC electrode.
    CrystEngComm 06/2013; 15(27):5442-5451. · 3.88 Impact Factor
  • Jianmin Wu, Longwei Yin, Luyuan Zhang
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    ABSTRACT: The modification of electronic structure, bandgap energy and photoluminescence properties of hexagonal boron nitride (h-BN) nanosheets has been challenging due to the inherent inertness and chemical stability of h-BN. In the present work, we realized tuning the electronic structure and bandgap energy properties of h-BN nanosheets via a controllable Ce3+ ions doping through a one-step facile thermal chemical reaction route using HBO3, C3H6N6 and Ce(Ac)3·nH2O as reactant precursors. As the Ce3+ ions incorporating content is lower than the critical threshold saturation value of 1.25%, the Ce-doped BN samples show an obvious band gap monotonically narrowing trend from 4.42 eV of pure BN to 3.31 eV for 1.25% Ce-doped BN nanosheets. With incorporation of Ce3+ ions into the lattice of h-BN, the intensity of electron paramagnetic resonance (EPR) signals closely associated with the nitrogen vacancies in Ce-doped BN samples, displays a decline trend with increasing the concentration of the incorporated Ce3+ ions, suggesting a decrease in the concentration of paramagnetic centers. The introduction of Ce3+ ions can result in the formation of a doping energy level between the conduction and valence bands of BN, and thus shifts the absorption band to the large-wavelength region, corresponding to the bandgap energy narrowing of Ce-doped BN, resulting in a red shift of the absorption edge of the Ce-doped BN samples. The B–N–O–Ce bonding due to the Ce3+ ion doping is responsible for bandgap energy narrowing in the Ce-doped BN materials. As the concentration of the incorporated Ce3+ ions reaches the critical threshold value of 1.25%, no more nitrogen vacancies are available, so the bandgap energy narrowing effect from the Ce3+ ion doping is reduced.
    RSC Advances 04/2013; 3(20):7408-7418. · 2.56 Impact Factor
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    ABSTRACT: Ordered mesoporous SnO2 materials with many regularly ordered pore channels, uniform size distribution, high surface area, highly crystalline state and good structural stability were synthesized via a facile infiltration chemical route. The synthesized ordered mesoporous SnO2 materials were characterized by X-ray diffraction, Brunauer–Emmett–Teller (BET) method, field emission scanning electron microscopy, and high resolution transmission electron microscopy. Cyclic voltammetry and galvanostatic techniques were utilized to characterize the electrochemical performance of the as prepared SnO2 samples as anode materials for lithium ion batteries. The ordered mesoporous SnO2 displays a good rate capability and cycling stability, exhibiting a high specific capacity of up to 557 mA h g−1, and a high coulombic efficiency of up to 98.5%, even after 40 cycles at a high current density of 100 mA g−1. The significant improvement of the electrochemical performance is attributed to the unique ordered mesoporous structure of SnO2 with a variety of favorable properties. The large surface area endows the synthesized SnO2 with more lithium storage sites and a large electrode–electrolyte contact area for high Li+ ions flux across the interface, a narrow mesopore size distribution is promised to render the liquid electrolyte diffusion into the bulk of the electrode material facile and hence to providing fast transport channels for the solvated Li+ ions, and the regularly ordered mesoporous structures are expected to buffer well against the local volume change during the Li–Sn alloying–dealloying reactions, and the interior space allows the volume variation upon insertion–extraction of lithium ions to be better accommodated.
    CrystEngComm 04/2013; 15(18):3696-3704. · 3.88 Impact Factor
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    ABSTRACT: We developed a facile one-step route to three-dimensional hybrids with Mn3O4 nanoparticles well and homogeneously embedded within ordered mesoporous carbon (OMC) for lithium ion battery applications. The Mn3O4/OMC hybrids with good rate capability and cycling stability display a high specific capacity up to 802 mA h g−1, and a high coulombic efficiency of up to 99.2% even after 50 cycles at a high current density of 100 mA g−1. This value is 1.6 times higher than the discharge capacity of 512 mA h g−1 for pure ordered OMC materials, and more than 5.4 times higher than the discharge value of 148 mA h g−1 for pure Mn3O4 nanoparticles. The enhanced capacity and cycling performance of the Mn3O4/OMC hybrids could be attributed to their unique robust three-dimensional composite structure and the synergistic effects between the Mn3O4 nanoparticles and OMC. The ordered mesostructured channels of Mn3O4/OMC hybrids are expected to buffer well against the local volume change during the Li uptake/removal reactions and thus to enhance the structural stability. The OMC matrix wall with a thickness of <10 nm greatly reduces the solid-state transport length for Li diffusion, and the hierarchical ordered mesoporosity facilitates the liquid electrolyte diffusion into the bulk of the electrode material and hence provides fast conductive ion transport channels for the conductive Li+ ions. The improved cycling performance can also be mainly attributed to good electrical contact between the Mn3O4 and OMC in the three-dimensional nanocomposites during phase transformation of Mn3O4 upon lithiation/delithiation that usually leads to capacity fading. This facile strategy can be extended to fabricate other ordered mesoporous carbon-encapsulated metal oxides.
    Journal of Materials Chemistry 07/2012; 22(32):16640-16648. · 5.97 Impact Factor
  • Dong Xiang, Longwei Yin
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    ABSTRACT: Ordered mesoporous carbon (OMC) supported well-dispersed PtFex nanoparticles with a controllable size distribution were prepared via a modified polyol synthesis route, using hexachloroplatinic acid and ferric chloride as Pt and Fe source, and ethylene glycol as a reducing agent. The catalytic activities relevant to direct methanol fuel cell of the PtFex/OMC composites were investigated using cyclic voltammetry, single-cell proton exchange membrane fuel cell (PEMFC) test and electrochemical impedance spectroscopy (EIS) technique. Due to the existence of more Pt0 species and Fe ion corrosion caused by the formation of the alloyed PtFex catalyst, Pt0 can provide the more active sites for methanol oxidation reaction, and the methanol oxidation activity of the PtFex/OMC electrode is evidenced to be enhanced by the increased anodic peak current with increasing the incorporation content of Fe. The oxygen reduction reaction (ORR) current density of 0.662 A cm−2 and power density of 237.2 mW cm−2 generated by the PtFe3/OMC sample are more than two times the values of 0.32 mA cm−2 and 102.6 mW cm−2 by the Pt/OMC sample. The PtFe3/OMC catalyst in 0.5 M H2SO4 + 1 M CH3OH displays the highest specific catalytic activity of 100.6 mA m−2, which is almost 3 times lower than that of 283.7 mA m−2 in 0.5 M H2SO4. The enhanced higher activity for the PtFe3/OMC sample can be firstly attributed to a highly homogeneous dispersion of the PtFe3 nanoparticles on the mesoporous channels within OMC, such PtFe3 nanoparticles with a diameter of 3.3 nm can accelerate the formation of Pt–OH groups. Meanwhile, the alloyed PtFe3 nanoparticles can provide a lower onset potential for the electrooxidation of CO/H2 than that of pure Pt, and would contribute more to the promotion of C–H breaking and COad tolerance. Furthermore, the larger surface area, the favorable pore structure and the structural integrity between the PtFe3 nanoparticles and the OMC matrix, will effectively facilitate the transportation of reactants and products in liquid electrochemical reactions.
    Journal of Materials Chemistry 04/2012; 22(19):9584-9593. · 5.97 Impact Factor
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    ABSTRACT: A facile one-step solvothermal reaction route to large-scale synthesis of carbon homogeneously wrapped manganese oxide (Mn(3)O(4)@C) nanocomposites for anode materials of lithium ion batteries was developed using manganese acetate monohydrate and polyvinylpyrrolidone as precursors and reactants. The synthesized Mn(3)O(4)@C nanocomposites were characterized by X-ray diffraction, field-emission scanning electron microscopy, high resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. The synthesized tetragonal structured Mn(3)O(4) (space group I41/amd) samples display nanorodlike morphology, with a width of about 200-300 nm and a thickness of about 15-20 nm. It is shown that the carbon layers with a thickness of 5 nm are homogeneously coated on the Mn(3)O(4) nanorods. It is indicated from lithium storage capacity estimation that the Mn(3)O(4)@C samples display enhanced capacity retention on charge/discharge cycling. Even after 50 cycles, the products remains stable capacity of 473 mA h g(-1), which is as much 3.05 times as that of pure Mn(3)O(4) samples. Because of the low-cost, nonpollution, and stable capacity, the carbon homogeneously coated Mn(3)O(4)@C nanocomposites are promising anode material for lithium ion batteries.
    ACS Applied Materials & Interfaces 03/2012; 4(3):1636-42. · 5.01 Impact Factor
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    ABSTRACT: ZnO and ZnO–CuO composite hollow spheres were fabricated by using colloidal carbon spheres as templates. The morphology, structure and chemical composition of the as-prepared samples were investigated using field emission scanning electron microscopy, transmission electron microscopy and X-ray diffraction. The photocatalytic activity of the hollow spherical products was evaluated by photocatalytic degradation of methylene blue (MB) aqueous solution at ambient temperature. The results indicated that the ZnO–CuO composite hollow spheres display higher photocatalytic efficiency than pure hollow ZnO products. The related photocatalytic mechanism was discussed based on the microstructure and properties of the ZnO and ZnO–CuO composite hollow spheres. The facile strategy for the preparation of ZnO–CuO hollow nanostructures can be applicable to the synthesis of other composite hollow spheres.
    Materials Letters. 01/2012; 67(1):303–307.
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    ABSTRACT: Magnetic ordered mesoporous carbons (OMCs) with Ni nanoparticle (average size: 10nm) homogeneously modified on surfaces of OMCs were successfully fabricated via a facile casting route. The microstructure, pore size distribution, pore structure, and surface area of the synthesized OMCs and Ni decorated OMCs (Ni-OMCs) were characterized by X-ray diffraction, field emission scanning electron microscopy, high-resolution transmission electron microscopy and N2 sorption. The characterization by magnetic hysteresis loops suggests a ferromagnetic behavior for the Ni-OMCs samples with a magnetization saturation of 2.34emug−1 at 300K, high enough for magnetic separation. The ferromagnetic Ni-OMCs were used as magnetically separable high-performance adsorbents for methyl orange (MO). The adsorption capacities for MO on the Ni-OMCs as magnetically separable adsorbents were investigated comparatively with pristine OMCs and activated carbon powder (ACP). The results show that the adsorption capacities for MO on the OMCs and Ni-OMCs adsorbents could be well described according to Langmuir isotherm with MO molecule preferentially adsorbed in the structured mesopores, suggesting the adsorption type of monolayer coverage of MO dye onto the mesoporous samples. The effects of surface area, pore structure, and the Ni deposition on the adsorption capacities for MO were systematically investigated. The effects of several important parameters such as contact time, temperature, adsorbent dosage and adsorbate concentration on the adsorption capabilities were studied in detail. The ferromagnetic Ni decorated OMCs as adsorbents for MO, were easily dispersed, separated and removed in an external applied magnet field, and can be more convenient for large scale applications than filtration or centrifugation separation route.
    Materials Chemistry and Physics - MATER CHEM PHYS. 12/2011;
  • Jianmin Wu, Longwei Yin
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    ABSTRACT: A novel amperometric biosensor based on the BNNTs-Pani-Pt hybrids with Pt nanoparticle homogeneously decorated on polyaniline (Pani)-wrapped boron nitride nanotubes (BNNTs), was developed. It is shown that π interactions take place between BNNTs and polyaniline (Pani) located at N atoms from BNNTs and C atoms from Pani, resulting in the water solubility for the Pani wrapped BNNTs hybrids. The developed glucose biosensor displayed high sensitivity and stability, good reproducibility, anti-interference ability, especially excellent acid stability and heat resistance. The resulted BNNTs-Pani-Pt hybrid amperometric glucose biosensor exhibited a fast response time (within 3 s) and a linear calibration range from 0.01 to 5.5 mM with a high sensitivity and low detection limit of 19.02 mA M(-1) cm(-2) and 0.18 μM glucose (S/N = 3). Surprisedly, the relative activity of the GC/BNNTs-Pani-Pt-GOD electrode keeps almost no change in a range from pH 3 to 7. Futhermore, the BNNTs-Pani-Pt hybrid biosensor maintains a high GOD enzymatic activity even at a relatively high temperature of 60 °C. This might be attributed to the effect of electrostatic field and hydrophobia of BNNTs. The unique acid stability and heat resistance of this sensor indicate great promising application in numerous industrial and biotechnological operations involving harsh conditions.
    ACS Applied Materials & Interfaces 11/2011; 3(11):4354-62. · 5.01 Impact Factor
  • Xifeng Lu, Longwei Yin
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    ABSTRACT: Porous indium oxide nanorods have been synthesized by calcination of indium hydroxide, which were prepared through a simple sol-gel and aging process at low temperature in the presence of sodium dodecyl sulfate (SDS). X-ray diffraction (XRD), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM) were adopted to characterize the phase composition and morphology of the resulted samples. The sensing properties towards H2 were examined at 340°C, which showed better sensitivity and quick response/recovery merits.
    Journal of Materials Science & Technology - J MATER SCI TECHNOL. 01/2011; 27(8):680-684.
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    ABSTRACT: We report on one-pot synthesis of PtRu nanoparticle modified ordered mesoporous carbons (OMCs) using RuCl3·xH2O and H2PtCl6·6H2O as ruthenium and platinum sources and ethylene glycol (EG) as reducing agent. PtRu alloyed nanoparticles with an average diameter of 3.6 nm were well decorated homogeneously both on the exterior surfaces and interior channels of the OMC matrix. A study on the effect of metal nanoparticle decoration on the structure, pore size, pore volume, and surface area of OMC matrix was carried out. The electrochemical hydrogen storage capacities of OMC/PtRu, OMC/Pt, and OMC are comparatively investigated using cyclic voltammetry and galvanostatic charge−discharge techniques. It is revealed that the PtRu nanoparticle modified OMC samples display an enhanced electrochemical hydrogen storage capacity of 411.8 mAh/g, almost 2.3 times higher than pure OMC electrode and 1.5 times higher than monometallic OMC/Pt electrode. The PtRu alloyed nanoparticles act as active hydrogen adsorption sites and thus increase the Had coverage degree due to its large surface area. The results indicated that the OMCs coated with PtRu nanoparticles can find potential applications for hydrogen storage.
    The Journal of Physical Chemistry C. 11/2010; 114(50).
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    ABSTRACT: Highly crystalline Pt nanoparticles with an average diameter of 5 nm were homogeneously modified on the surfaces of TiO(2) nanowires (Pt-TiO(2) NWs) by a simple hydrothermal and chemical reduction route. Photodegradation of methylene blue (MB) in the presence of Pt-TiO(2) NWs indicates that the photocatalytic activity of TiO(2) NWs can be greatly enhanced by Pt nanoparticle modification. The physical chemistry process and photocatalytic mechanism for Pt-TiO(2) NWs hybrids degrading MB were investigated and analyzed. The Pt attached on TiO(2) nanowires induces formation of a Schottky barrier between TiO(2) and Pt naonoparticles, leading to a fast transport of photogenerated electrons to Pt particles. Furthermore, Pt incoporation on TiO(2) surface can accelerate the transfer of electrons to dissolved oxygen molecules. Besides enhancing the electron-hole separation and charge transfer to dissolved oxygen, Pt may also serve as an effective catalyst in the oxidation of MB. However, a high Pt loading value does not mean a high photocatalytic activity. Higher content loaded Pt nanoparticles can absorb more incident photons which do not contribute to the photocatalytic efficiency. The highest photocatalytic activity for the Pt-TiO(2) nanohybrids on MB can be obtained at 1 at % Pt loading.
    ACS Applied Materials & Interfaces 10/2010; 2(11):3373-7. · 5.01 Impact Factor
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    ABSTRACT: Three-dimensional (3D) crystalline anatase titanium dioxide (TiO(2)) hierarchical nanostructures were synthesized through a facile and controlled hydrothermal and after-annealing process. The formation mechanism for the anatase TiO(2) 3D hierarchical nanostructures was investigated in detail. The 3D hierarchical nanostructures morphologies are formed by self-organization of several tens of radially distributed thin petals with a thickness of several nanometers with a larger surface area. The surface area of TiO(2) hierarchical nanostructures determined by the Brunauer-Emmett-Teller (BET) adsorption isotherms was measured to be 64.8 m(2) g(-1). Gas sensing properties based on the hierarchical nanostructures were investigated. A systematic study on sensitivity as a function of temperatures and gas concentrations was carried out. It reveals an improved ethanol gas sensing response property with a sensitivity of about 6.4 at 350 degrees C upon exposure to 100 ppm ethanol vapor for the TiO(2) hierarchical nanostructures. A gas sensing mechanism based on the adsorption-desorption of oxygen on the surface of TiO(2) is discussed and analyzed. This novel gas sensor can be multifunctional and promising for practical applications. Furthermore, the hierarchical nanostructures with high surface area can find variety of potential applications such as solar cells, biosensors, catalysts, etc.
    Langmuir 08/2010; 26(15):12841-8. · 4.19 Impact Factor
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    ABSTRACT: The hexagonal faceted ZnO quantum dots (QDs) about 3-4 nm have been prepared via a sol-gel route by using oleic acid (OA) as the capping agent. It is revealed by electron diffraction patterns and high resolution transmission electron microscopy lattice images that the profile surfaces of the highly crystalline ZnO QDs are mainly composed of {100} planes, with the Zn-terminated (001) faces and the opposite (001) faces presented as polar planes. Compared with spherical ZnO QDs, the hexagonal faceted ZnO QDs show enhanced photocatalytic activity for photocatalytic decomposition of methylene blue. A mechanism for the enhanced photocatalytic activity of the hexagonal faceted ZnO QDs for degradation of methylene blue is proposed. In addition to the large specific surface areas due to small size and high crystalline, the enhanced photocatalytic activity can mainly be ascribed to the special hexagonal morphology. The Zn-terminated (001) and O-terminated (001) polar faces are facile to adsorb oxygen molecules and OH(-) ions, resulting in a greater production rate of H(2)O(2) and OH(*) radicals, hence promoting the photocatalysis reaction. The synthesized hexagonal-shaped ZnO QDs with high photocatalytic efficiency will find widespread potential applications in environmental and biological fields.
    ACS Applied Materials & Interfaces 06/2010; 2(6):1769-73. · 5.01 Impact Factor
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    ABSTRACT: To get a real understanding on the complexity of origin and mechanism of visible emission for ZnO quantum dots (QDs), we systematically property of visible emission of ZnO QDs with tunable diameters in a range of 2.2−7.8 nm synthesized via a sol−gel route using self-made zinc−oleate complex as a precursor. It is indicated that the visible emission of ZnO QDs can be ascribed to singly ionized oxygen vacancies, which is associated with the paramagnetic centers with electron paramagnetic resonance (EPR) value of g = 2.0056. The visible emission property of the ZnO QDs displays highly size-dependent behavior. With ZnO QDs size decreasing, the visible emission peaks blue-shift to the positions with shorter wavelength due to quantum size effect, however, is different from that of band gap. Quantitative investigation shows that the visible emission can correspond to a transition of holes from the valence band to the preexisting deep donor energy level, which is different from the well-known conclusion that the visible emission is due to the transition of an electron from the conduction band to a deep trap. Two important points can be obtained: the defects of singly ionized oxygen vacancies determine the origin and intensity of visible emission of ZnO QDs; and the visible emission peak position of ZnO QDs is decided by their size, and a transition of holes from the valence band to the preexisting deep donor energy level is responsible for the visible emission of the ZnO QDs.
    Journal of Physical Chemistry C - J PHYS CHEM C. 05/2010; 114(21).
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    ABSTRACT: TiO2 nantube arrays (NTAs) with a tube diameter of about 100 nm were prepared by anodic oxidation, and a Ni layer about several tens of micrometers thick was electrodeposited on the surface of TiO2 NTAs. The synthesized Ti/TiO2 NTA/Ni composite electrodes were used for nonenzymatic glucose detection. The behavior of the anodic TiO2 NTA/substrate Ti metal is analogous to characteristics of an n-type semiconductor/metal Schottky barrier diode. The characteristic would enhance the rapid transport of surface reaction electrons to the metal substrate, thereby enhancing the performance of biosensors. Cyclic voltammogram investigations indicate that calcined Ti/TiO2 NTAs have a wider work potential window than that of Ti/TiO2 NTAs without calcinations and Ti foils. Moreover, the low saturated current in alkaline solutions under a constant potential makes Ti/TiO2 NTAs favorable as substrate materials for biosensors. For the Ti/TiO2 NTA/Ni composite electrodes, the relationship between the linear range and the potential was investigated. The positive line scans and the amperometric response curves to glucose indicated that a potential of 0.5−0.6 V would be favorable to get a wide linear range for detecting glucose. The sensitivity of the composite electrodes can reach a value as high as 200 μA mM−1 cm−2, and the detection limit was about 4 μM with a signal-to-noise ratio of 3 (S/N = 3). The present Ti/TiO2 NTA/Ni composite nonenzymatic amperometric glucose sensor could find potential applications in a good biosensing platform for other redox proteins and enzymes.
    Journal of Physical Chemistry C - J PHYS CHEM C. 02/2010; 114(10).
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    ABSTRACT: Mesoporous nitrogen-doped carbon (N-MC) with highly ordered two dimensional hexagonal structures has been synthesized using diaminobenzene (DAB) as carbon and nitrogen sources, ammonium peroxydisulfate (APDS) as an oxidant, and SBA-15 as a hard template. The effect of synthesis temperatures and precursors on the textures and nitrogen content of the N-MC is investigated. By adjusting the synthesis temperatures in a range of 70–100 °C, the pore diameter of the N-MC materials can be tuned from 3.43 to 4.15 nm, while the specific surface area of the N-MC with a nitrogen content of 26.5 wt.%, can be tuned from 281.8 to 535.2 m2/g. The C/N molar ratio of the N-MC can be tuned in a range of 3.25–3.65 by adjusting the mole ratio of DAB/APDS precursors at a synthesis temperature of 80 °C, while the pore diameter of the N-MC be tuned in a range of 4.12–3.66 nm. With the nitrogen doping content increasing, the lattice constant of N-MC materials decreases. Investigation indicates that well ordered N-MC materials with large specific surface area, high total pore volume and high nitrogen content can be fabricated under a synthesis temperature of 80 °C and a molar ratio of 1.5 for DAB/APDS precursors.
    Carbon. 01/2010;