Ningzhong Bao

Nanostructured WO3/BiVO4 Heterojunction Films for Efficient Photoelectrochemical Water Splitting

We report on a novel heterojunction WO(3)/BiVO(4) photoanode for photoelectrochemical water splitting. The heterojunction films are prepared by solvothermal deposition of a WO(3) nanorod-array film onto fluorine-doped tin oxide (FTO) coated glass, with subsequent deposition of a low bandgap, 2.4 eV, visible light responding BiVO(4) layer by spin-coating. The heterojunction structure offers enhanced photoconversion efficiency and increased photocorrosion stability. Compared to planar WO(3)/BiVO(4) heterojunction films, the nanorod-array films show significantly improved photoelectrochemical properties due, we believe, to the high surface area and improved separation of the photogenerated charge at the WO(3)/BiVO(4) interface. Synthesis details are discussed, with film morphologies and structures characterized by field emission scanning electron microscopy and X-ray diffraction.

Synthesis of Shape-Controlled Monodisperse Wurtzite CuInxGa1–xS2 Semiconductor Nanocrystals with Tunable Band Gap

Monodisperse wurtzite CuIn(x)Ga(1-x)S(2) nanocrystals have been synthesized over the entire composition range using a facile solution-based method. Depending on the chemical composition and synthesis conditions, the morphology of the nanocrystals can be controlled in the form of bullet-like, rod-like, and tadpole-like shapes. The band gap of the nanocrystals increases linearly with increasing Ga concentration, with band gap values for the end members being close to those observed in the bulk. Colloidal suspensions of the nanocrystals are attractive for use as inks for low-cost fabrication of thin film solar cells by spin or spray coating.

Synthesis and deposition of ultrafine Pt nanoparticles within high aspect ratio TiO2 nanotube arrays: application to the photocatalytic reduction of carbon dioxide

Using a rapid microwave-assisted solvothermal approach ultrafine Pt nanoparticles are synthesized and deposited in situ within high aspect ratio nanotube arrays. Adjusting the initial concentration of metal ion precursor inside the nanotube support controls the resulting Pt nanoparticle sizes. The Pt-nanoparticle/TiO2 nanotube composite is shown to greatly promote the photocatalytic conversion of carbon dioxide and water vapor into methane, a behavior attributed to the homogeneous distribution of metal co-catalyst nanoparticles over the TiO2 nanotube array surface providing a large number of active reduction sites. The novelty and flexibility of the technique, described herein, could prove useful for the deposition of metal, metal alloy, or metal oxide nanoparticles within a variety of nanotubular or nanoporous material systems with the resulting nanocomposites useful in catalysis, photocatalysis, photovoltaic, and photoelectrochemical applications.

Direct synthesis of ZnO nanoparticles by a solution-free mechanochemical reaction

This paper presents a study on the synthesis and characterization of ZnO nanoparticles by a two-step synthesis procedure. The first step is the solution-free mechanochemical synthesis of ZnC2O4?2H2O nanoparticles by grinding a powder mixture of Zn(CH3COO)2 and H2C2O4?2H2O at room temperature for a certain time. The second step is the thermal decomposition of ZnC2O4?2H2O nanoparticles at 450??C to form ZnO nanoparticles. The obtained ZnO nanoparticles have been structurally characterized by x-ray diffraction, indicating a wurtzite structure (hexagonal phase, space group P63mc) with high crystallinity. The average grain size of the ZnO nanoparticles is in the range of 24?40?nm, depending on the mechanical grinding time. The UV?vis diffuse reflectance spectrum of the ZnO nanoparticles indicates a band gap of about 3.3?eV with an onset of absorption at about 3.1?eV, showing a weak red shift compared to 3.37?eV for the bulk ZnO. X-ray photoelectron spectroscopy and Raman spectra showed a nonadsorption on the surface and a very low concentration of oxygen vacancies, respectively, indicating a high quality of the prepared ZnO nanoparticles. The formation process of the ZnC2O4?2H2O nanoparticles by?the solution-free mechanochemical reaction is discussed.

Controlled Growth of Monodisperse Self-Supported Superparamagnetic Nanostructures of Spherical and Rod-Like CoFe2O4 Nanocrystals

Novel shape- and structural-controlled superparamagnetic nanostructures composed of self-supported spherical and rod-like CoFe(2)O(4) colloidal nanocrystals have been prepared by thermolysis of a stoichiometric Co(2+)Fe(2)(3+)-oleate complex in organic solution with periodic injection of hexane for controlling the nucleation, assembly, and growth of the nuclei.

Fabrication of coaxial TiO2/Sb2S3 nanowire hybrids for efficient nanostructured organic–inorganic thin film photovoltaics

We report on low-cost, all solution fabrication of efficient air-stable nanostructured thin film photovoltaics comprised of n-type Sb(2)S(3) chemically deposited onto TiO(2) nanowire array films, forming coaxial Sb(2)S(3)/TiO(2) nanowire hybrids vertically oriented from the SnO(2):F coated glass substrate, which are then intercalated with poly(3-hexylthiophene) (P3HT) for hole transport and enhanced light absorption.

Size-controlled one-dimensional monocrystalline BaTiO3 nanostructures

One-dimensional BaTiO3 nanostructures have been synthesized by a simple hydrothermal ion-exchange reaction using alkali-metal titanates as synthetic precursors. The BaTiO3 nanowires obtained from Na2Ti3O7 nanowires have diameters of 50–80 nm and lengths of up to 10 μm. In contrast, BaTiO3 nanowires obtained from K2Ti4O9 nanowhiskers have relatively large sizes of 300–500 nm in diameter and several tens of microns in length. Both types of nanostructures are single-crystalline without any impurity phases. The local electric polarization of individual ferroelectric nanowires has been studied using vertical mode piezoresponse force microscopy.

Colloidal synthesis of wurtzite Cu2CoSnS4 nanocrystals and the photoresponse of spray-deposited thin films

Monodisperse nanocrystals of a new wurtzite phase of Cu(2)CoSnS(4) (CCTS) have been synthesized using a simple solution-based method. The wurtzite CCTS nanocrystals grow in the shape of nanorods with an average length of 32 ± 2.0 and width of 16 ± 1.5 nm. The more stable stannite phase of CCTS has also been synthesized by increasing the reaction temperature or by a post-high-temperature annealing process. The band gap of wurtzite CCTS nanocrystals is determined to be 1.58 eV. Thin films prepared from the nanocrystal suspension display photoresponse behaviour with white light from a solar simulator, suggesting the potential use of CCTS as an active layer in low-cost thin-film solar cells.

Double-Sided Brush-Shaped TiO2 Nanostructure Assemblies with Highly Ordered Nanowires for Dye-Sensitized Solar Cells

We describe a seeded hydrothermal process for the growth of unique double-sided brush-shaped (DSBS) TiO2 nanostructure assemblies consisting of highly ordered rutile nanowires vertically aligned around an annealed TiO2 nanoparticle layer. The annealed TiO2 nanoparticle layer seeds the nanowire growth and also supports the DSBS structure. The morphology of the DSBS TiO2 nanostructure depends on the hydrothermal reaction time. The diameter of the nanowires is about 6.6 nm, and with increasing reaction time from 1 to 8 h the nanowire length increases from 0.6 to 6.2 μm, whereas the thickness of the nanoparticle layer decreases from 4.3 to 2.8 μm. These free-standing nanowire arrays provide large internal surface area, which is essential for minimizing carrier recombination in high performance photovoltaic devices. Furthermore, the nanowire architecture can help increase the rate of charge transport as compared to particulate films because of lower concentration of grain boundaries. The power conversion efficiency of backside (DSBS TiO2/FTO photoanode) illuminated dye-sensitized solar cells fabricated using the DSBS TiO2 nanostructure assembly is found to be depended on the nanowire length. A cell fabricated using 15.2 μm thick nanostructures sensitized by N719 has a short-circuit current density of 12.18 mA cm(-2), 0.78 V open circuit potential, and a 0.59 filling factor, yielding a maximum power conversion efficiency of 5.61% under AM 1.5 illumination.

Efficient Thermolysis Route to Monodisperse Cu 2 ZnSnS 4 Nanocrystals with Controlled Shape and Structure

Monodisperse Cu2ZnSnS4 (CZTS) nanocrystals with tunable shape, crystalline phase, and composition are synthesized by efficient thermolysis of a single source precursor of mixed metal-oleate complexes in hot organic solvents with dissolved sulfur sources. Suitable tuning of the synthetic conditions and the Cu/(Zn + Sn) ratio of the precursor has enabled precise control of the crystalline phase in the form of kesterite, or a newly observed wurtzite structure. Nanocrystals with morphology in the form of spherical, rice-like, or rod-like shapes are obtained over a wide range of compositions (0.5 ≤ Cu/(Zn + Sn) ≤ 1.2). Both the final products and intermediates for each shape exhibit consistent composition and structure, indicating homogenous nucleation and growth of single-phase nanocrystals. Thin films prepared from colloidal nanocrystal suspensions display interesting shape-dependent photoresponse behavior under white light illumination from a solar simulator.