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ABSTRACT: ZnO-TiO(2)-reduced graphene oxide (RGO) composites were successfully synthesized by microwave-assisted reduction of graphite oxide in ZnO precursor solution with TiO(2) suspension using a microwave synthesis system. Their morphology, structure, and photocatalytic performance in the reduction of Cr(VI) were characterized by scanning electron microscopy, X-ray diffraction spectroscopy, and UV-vis absorption spectrophotometer. The results show that ZnO-TiO(2)-RGO composites exhibit an enhanced photocatalytic performance in reduction of Cr(VI) with a maximum removal rate of 99.4% under UV light irradiation as compared with pure ZnO (58%) and ZnO-RGO (98%) composites due to the increased light absorption intensity and the reduction of electron-hole pair recombination in ZnO with the introduction of TiO(2).
Journal of Colloid and Interface Science 12/2012; · 3.07 Impact Factor
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ABSTRACT: A reduced graphene (RG)-Au nanoparticle composite film is successfully fabricated by electrophoretic deposition and used as counter electrode for quantum dot-sensitized solar cells. The RG-Au composite is prepared by one-step microwave-assisted reduction of chloroaurate in alkaline solution with graphite oxide dispersion. Under one sun illumination (AM 1.5 G, 100 mW cm(-2)), the cell with a RG-Au counter electrode shows an energy conversion efficiency of 1.36 %, which is higher than those of cells employing conventional Pt or Au counter electrodes, due to the superior combination of highly catalytic Au nanoparticles and the conductive graphene network structure.
ChemPhysChem 02/2012; 13(3):769-73. · 3.41 Impact Factor
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ABSTRACT: Y(3)Al(5)O(12):Ce phosphors have been prepared and used as an effective scattering layer on top of a transparent layer of nanocrystalline TiO(2) for dye sensitized solar cells (DSSCs). The Y(3)Al(5)O(12):Ce scattering layer increases the photocurrent of DSSCs due to the enhanced light harvesting mainly via the improved light absorption and scattering. Under one sun illumination (AM 1.5G, 100 mW cm(-2)), a high efficiency of 7.91% was achieved for the cell with a Y(3)Al(5)O(12):Ce scattering layer, which is an increase of 13.5% compared to the cell without a scattering layer (6.97%).
Chemical Communications 11/2011; 48(7):958-60. · 6.17 Impact Factor
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ABSTRACT: CdS-reduced graphene oxide (RGO) composites are successfully synthesized via the microwave-assisted reduction of graphite oxide in a CdS precursor solution using a microwave synthesis system. The photocatalytic performances of CdS-RGO composites in the reduction of Cr(VI) are investigated. The results show that CdS-RGO composites exhibit enhanced photocatalytic performance for the reduction of Cr(VI) with a maximum removal rate of 92% under visible light irradiation as compared with pure CdS (79%) due to the increased light absorption intensity and the reduction of electron-hole pair recombination in CdS with the introduction of RGO.
Chemical Communications 09/2011; 47(43):11984-6. · 6.17 Impact Factor
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ABSTRACT: A facile and pollution-free method was applied to prepare graphene nanosheets by reducing graphene oxide in acidic aqueous solution without any toxic chemicals via microwave heating. The surface morphology, structure, and composition characterizations were carried out using atomic force microscopy, field-emission scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, and Raman spectroscopy, respectively. The results showed that high-quality and large-area reduced graphene nanosheets were obtained.
Physica Status Solidi (A) Applications and Materials 08/2011; 208(10):2325 - 2327. · 1.46 Impact Factor
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ABSTRACT: A CdS/CdSe quantum-dot (QD)-cosensitized TiO(2) film has been fabricated using a microwave-assisted chemical bath deposition technique and used as a photoanode for QD-sensitized solar cells. The technique allows a direct and rapid deposition of QDs and forms a good contact between QDs and TiO(2) films. The photovoltaic performance of the as-prepared cell is investigated. The results show that the performance of the CdS/CdSe-cosensitized cell achieves a short-circuit current density of 16.1 mA cm(-2) and a power conversion efficiency of 3.06% at one sun (AM 1.5 G, 100 mW cm(-2)), which is comparable to the one fabricated using conventional successive ionic layer adsorption and reaction technique.
ACS Applied Materials & Interfaces 07/2011; 3(8):3146-51. · 4.53 Impact Factor
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ABSTRACT: Sensitized-type solar cells based on TiO₂ photoanodes and CdS quantum dots (QDs) as sensitizers have been studied. CdS QDs are grown on TiO₂ films, utilizing one-step microwave assisted chemical bath deposition (MACBD) method. This method allows a facile and rapid deposition and integration between CdS QDs and TiO₂ films. The photovoltaic performances of the cells fabricated using CdS precursor solutions with different concentrations are investigated. The results show that the cell based on MACBD deposited TiO₂/CdS electrode achieves a maximum short circuit current density of 7.20 mAcm⁻² and power conversion efficiency of 1.18 % at one sun (AM 1.5G, 100 mW cm⁻²), which is comparable to the ones prepared using conventional techniques.
ACS Applied Materials & Interfaces 05/2011; 3(5):1472-8. · 4.53 Impact Factor
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ABSTRACT: Herein we report a novel, environment-friendly approach for the reduction of graphene oxide by means of incorporating visible-light sensitive TiO2 and steady state visible-light irradiation. The surface morphology and fine structure of as-prepared composites were characterized by scanning electron microscopy and atomic force microscopy, respectively. The reduction process was evidenced by variation of conductivity. In addition, some of the electrochemical properties of the resultant graphene materials have been investigated as well.
Journal of Materials Research. 04/2011; 26(08):970 - 973.
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ABSTRACT: CdSe quantum dot (QD ) sensitized TiO(2) films have been fabricated using a one-step microwave assisted chemical bath deposition (MACBD) technique and used as photoanodes for quantum dot sensitized solar cells. This technique allows direct and rapid deposition and a good contact between the CdSe and TiO(2) films. The photovoltaic performances of the cells with CdSe deposited at different times are investigated. The results show that cells based on MACBD deposited TiO(2)/CdSe electrodes achieve a maximum short circuit current density of 12.1 mA cm(-2) and a power conversion efficiency of 1.75% at one Sun (AM 1.5 G, 100 mW cm(-2)), which is comparable with those fabricated using conventional techniques.
Nanoscale 03/2011; 3(5):2188-93. · 5.91 Impact Factor
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ABSTRACT: The kinetics, thermodynamics, and isotherms during electrical removal of Cu 2+ by carbon nanotube and carbon nanofiber (CNT-CNF) electrodes in CuCl 2 solution were studied under different solution temperatures, initial Cu 2+ concentrations, and applied voltages. The result shows that Langmuir isotherm can describe experimental data well, indicating monolayer adsorption, and higher Cu 2+ removal and rate constant are achieved at higher voltage, lower initial Cu 2+ concentration, and higher solution temperature. Meanwhile, the thermodynamics analyses indicate that the electrical removal of Cu 2+ onto CNT-CNF electrodes is mainly driven by a physisorption process.
SAGE-Hindawi Access to Research International Journal of Electrochemistry. 01/2011; 8.
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ABSTRACT: The chemistry and physics of under-coordination at a surface, which determines the process of catalytic reactions and growth nucleation, is indeed fascinating. However, extracting quantitative information regarding the coordination-resolved surface relaxation, binding energy, and the energetic behavior of electrons localized in the surface skin from photoelectron emission has long been a great challenge, although the surface-induced core level shifts of materials have been intensively investigated. Here we show that a combination of the theories of tight binding and bond order-length-strength (BOLS) correlation [C. Q. Sun, Prog. Solid State Chem., 2007, 35, 1-159], and X-ray photoelectron spectroscopy (XPS) has enabled us to derive quantitative information, by analyzing the Be 1s energy shift of Be(0001), (1010), and (1120) surfaces, for demonstration, regarding: (i) the 1s energy level of an isolated Be atom (106.416 ± 0.004 eV) and its bulk shift (4.694 eV); (ii) the layer- and orientation-resolved effective atomic coordination (3.5, 3.1, 2.98 for the first layer of the three respective orientations), local bond strain (up to 19%), charge density (133%), quantum trap depth (110%), binding energy density (230%), and atomic cohesive energy (70%) of Be surface skins up to four atomic layers in depth. It is affirmed that the shorter and stronger bonds between under-coordinated atoms perturb the Hamiltonian and hence the fascinating localization and densification of surface electrons. The developed approach can be applied to other low-dimensional systems containing a high fraction of under-coordinated atoms such as adatoms, atomic defects, terrace edges, and nanostructures to gain quantitative information and deeper insight into their properties and processes due to the effect of coordination imperfection.
Physical Chemistry Chemical Physics 10/2010; 12(39):12753-9. · 3.57 Impact Factor
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ABSTRACT: Capacitive deionization (CDI) is a novel technology that has been developed for removal of charged ionic species from salty water, such as salt ions. The basic concept of CDI, as well as electrosorption, is to force charged ions toward oppositely polarized electrodes through imposing a direct electric field to form a strong electrical double layer and hold the ions. Once the electric field disappears, the ions are instantly released back to the bulk solution. CDI is an alternative low-energy consumption desalination technology. Graphene-like nanoflakes (GNFs) with relatively high specific surface area have been prepared and used as electrodes for capacitive deionization. The GNFs were synthesized by a modified Hummers' method using hydrazine for reduction. They were characterized by atomic force microscopy, N2 adsorption at 77 K and electrochemical workstation. It was found that the ratio of nitric acid and sulfuric acid plays a vital role in determining the specific surface area of GNFs. Its electrosorption performance was much better than commercial activated carbon (AC), suggesting a great potential in capacitive deionisation application. Further, the electrosorptive performance of GNFs electrodes with different bias potentials, flow rates and ionic strengths were measured and the electrosorption isotherm and kinetics were investigated. The results showed that GNFs prepared by this process had the specific surface area of 222.01 m²/g. The specific electrosorptive capacity of the GNFs was 23.18 µmol/g for sodium ions (Na+) when the initial concentration was at 25 mg/L, which was higher than that of previously reported data using graphene and AC under the same experimental condition. In addition, the equilibrium electrosorption capacity was determined as 73.47 µmol/g at 2.0 V by fitting data through the Langmuir isotherm, and the rate constant was found to be 1.01 min⁻¹ by fitting data through pseudo first-order adsorption. The results suggested that the chemically synthesized GNFs can be used as effective electrode materials in CDI process for brackish water desalination.
Environmental Science & Technology 10/2010; 44(22):8692-7. · 4.80 Impact Factor
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ABSTRACT: Quantum dot-sensitized solar cells based on Zn-doped TiO(2) (Zn-TiO(2)) film photoanode and polysulfide electrolyte were fabricated. Zn-TiO(2) nanoparticles were obtained via a hydrothermal method and screen printed on the fluorine-doped tin oxide glass to prepare the photoanode. The structure, morphology and impedance of the Zn-TiO(2)/CdS film and the photovoltaic performance of the Zn-TiO(2)/CdS cell were investigated. It was found that the photovoltaic efficiency was improved by 24% when the Zn-TiO(2) film was adopted as the photoanode of CdS QDSSCs instead of only the TiO(2) layer. The improvement was ascribed to the reduction of electron recombination and the enhancement of electron transport in the TiO(2) film by Zn doping.
Nanoscale 07/2010; 2(7):1229-32. · 5.91 Impact Factor
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ABSTRACT: Dispersed and spherical Y2O3:Eu3+ red phosphor particles were prepared by the urea homogeneous precipitation method. In2O3 nanoparticles were successfully coated on the surface of the phosphor. Phase compositions, morphologies, photoluminescence (PL) spectra, and cathodoluminescence (CL) properties of Y2O3:Eu3+ phosphors before and after In2O3 coating were examined. It was found that CL properties such as luminous efficiency, lifetime, and stability of In2O3-coated phosphor screen were improved significantly, even though its PL intensity decreased compared with that of the uncoated sample. The reason is attributed to the increase of the electrical conductivity and the decrease of the charge accumulating effect. The present results prove that Y2O3:Eu3+ phosphor coated with an appropriate amount of In2O3 is more suitable to the requirement for low-voltage field-emission displays.
International Journal of Applied Ceramic Technology 06/2010; 8(4):752 - 758. · 1.38 Impact Factor
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ABSTRACT: The ability of a catalyst to accept or donate charge is the key to the process of catalytic reaction. However, the determination of the catalytic nature of a specimen as yet remains a great challenge. Here we report an effective yet simple method for this purpose based on the tight binding theory considerations and XPS monitoring of the evolution of valence and core electrons upon alloy formation. Firstly, we measured the valence and core band charge density of the constituent elements of Cu, Ag, and Pd and then the respective states upon alloy formation. A subtraction of the resultant spectrum of the alloy by the composed elemental spectra gives the residual that shows clearly the occurrence of charge trapping or polarization. We found that the valence and the core electrons of the CuPd alloy shift positively to deeper energies, opposite to the occurrences in the AgPd alloy. Findings clarify for the first time that CuPd serves as an acceptor due to quantum trapping and the AgPd as a donor because of charge polarization, which also explain why AgPd and CuPd perform very differently as important catalysts.
Physical Chemistry Chemical Physics 04/2010; 12(13):3131-5. · 3.57 Impact Factor
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ABSTRACT: Incorporating the BOLS correlation algorithm [Y. Sun, J. Phys. Chem. C, 2009, 113, 14696] into high-resolution XPS measurements [J. N. Andersen, et al., Phys. Rev. B: Condens. Matter, 1994, 50, 17525; A. Baraldi, et al., New J. Phys., 2007, 9, 143] has produced an effective way of determining the 3d(5/2) energy levels of isolated Rh(302.163 +/- 0.003 eV) and Pd (330.261 +/- 0.004 eV eV) atoms and their respective bulk shifts (4.367 and 4.359 eV) with a refinement of the effective atomic coordination numbers of the top (100), (110), and (111) atomic layers (4.00, 3.87, and 4.26, respectively). It is further confirmed that the shorter and stronger bonds between under-coordinated atoms induce local strain and skin-depth charge-and-energy quantum trapping and, hence, dictate globally the positive core level binding energy shifts.
Physical Chemistry Chemical Physics 03/2010; 12(9):2177-82. · 3.57 Impact Factor
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ABSTRACT: a b s t r a c t The carbon nanotubes and carbon nanofibers composite films (CNTs–CNFs) were fabricated by chemical vapor deposition. The electrosorption performance of CNTs–CNFs films at different solution temperatures was studied. It is found that the salt removal decreases from 45.4% to 33% due to hydrophobic–hydro-philic transition taking place on the surface of CNTs–CNFs films, when solution temperature ranges from 281 to 295 K. The electrosorption isotherm investigation shows Langmuir isotherm can better describe experimental data. Meanwhile, the kinetics and thermodynamics analyses indicate that the electrosorp-tion of NaCl onto CNTs–CNFs electrodes follows first-order kinetics model and is driven by a physisorp-tion process.
01/2010;
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ABSTRACT: Quantum dot-sensitized solar cells based on fluorine-doped tin oxide (FTO)/Au/TiO(2)/CdS photoanode and polysulfide electrolyte are fabricated. Au nanoparticles (NPs) as interfacial layer between FTO and TiO(2) layer are dip-coated on FTO surface. The structure, morphology and impedance of the photoanodes and the photovoltaic performance of the cells are investigated. A power conversion efficiency of 1.62% has been obtained for FTO/Au/TiO(2)/CdS cell, which is about 88% higher than that for FTO/TiO(2)/CdS cell (0.86%). The easier transport of excited electron and the suppression of charge recombination in the photoanode due to the introduction of Au NP layer should be responsible for the performance enhancement of the cell.
Nanoscale Research Letters 01/2010; 5(11):1749-1754. · 2.73 Impact Factor
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ABSTRACT: Low cost and large scale carbon nanotube and nanofibre (CNT-CNF) composite films have been fabricated and employed as electrodes for electrosorption of cupric ions. The regeneration of the saturated CNT-CNF film electrode has been investigated. Three methods (short-circuiting, short-circuiting and then reversing voltage, reversing voltage and then short-circuiting) are used for regeneration. The results show that low regeneration efficiency of CNT-CNF film electrode due to electrodeposition of Cu on the electrode surface can be highly improved by regeneration applying reverse voltage combined with short circuit. 93% regeneration efficiency can be achieved when 0.8 V reverse voltage is applied before short-circuiting during regeneration of CNT-CNF film electrode.
Water Science & Technology 01/2010; 61(6):1427-32. · 1.12 Impact Factor
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Chang Q. Sun,
Yi Sun,
Yanguang Ni,
Xi Zhang,
Jisheng Pan,
Xiao-Hui Wang,
Ji Zhou,
Long-Tu Li,
Weitao Zheng,
Shansheng Yu,
L. K. Pan, Zhuo Sun
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ABSTRACT: Superhydrophobicity, superfluidity, superlubricity, and supersolidity (4S) at the nanometer-sized liquid−solid or solid−solid contacting interfaces have long been issues of puzzling with the common characteristics of nonsticky and frictionless motion. Although the 4S occurrences have been extensively investigated, the mechanism behind the common characteristics remains unclear. From the perspectives of broken-bond-induced local strain and the skin-depth charge and energy quantum trapping and the associated nonbonding electron polarization, we proposed herewith that the Coulomb repulsion between the “electric monopoles or dipoles locked in the elastic solid skins or the solidlike covering sheets of liquid droplets” forms the key to the 4S. The localized energy densification makes the skin stiffer and the densely and tightly trapped bonding charges polarize nonbonding electrons, if exist, to form locked skin monopoles. In addition, the sp-orbit hybridization of F, O, N, or C upon reacting with solid atoms generates nonbonding lone pairs or unpaired edge electrons that induce dipoles directing into the open end of a surface. The monopoles and dipoles can be, however, demolished by UV radiation, thermal excitation, or excessively applied compression due to ionization or sp orbit dehybridization. Such a Coulomb repulsion between the negatively charged skins of the contacting objects not only lowers the effective contacting force and hence the friction but also prevents charge from being exchanged between the counterparts of the contact. Being similar to magnetic levitation, such Coulomb repulsion should be the force driving the 4S. Density function theory calculations, X-ray photoelectron spectroscopy, scanning tunneling microscopy/spectroscopy, and very low energy electron diffraction measurements have been conducted to verify the proposal. In particular, agreement between theory predictions and the measured size dependence of the elastic modulus, lattice strain, core−electron binding energy shift, and band gap expansion of nanostructures evidence the validity of the proposal of interface Coulomb repulsion.
11/2009;
