Xinjian Feng

Pennsylvania State University, University Park, MD, United States

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Publications (14)99.7 Total impact

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    ABSTRACT: 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.
    Chemical Communications 02/2012; 48(22):2818-20. · 6.38 Impact Factor
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    ABSTRACT: A rapid solvothermal approach was used to synthesize aligned 1D single-crystal rutile TiO(2) nanowire (NW) arrays on transparent conducting substrates as electrodes for dye-sensitized solar cells. The NW arrays showed a more than 200 times faster charge transport and a factor four lower defect state density than conventional rutile nanoparticle films.
    Angewandte Chemie International Edition 02/2012; 51(11):2727-30. · 11.34 Impact Factor
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    ABSTRACT: We review the use of self-assembled, vertically oriented one-dimensional (1D) titania nanowire and nanotube geometries in several third-generation excitonic solar cell designs including those based upon bulk heterojunction, ordered heterojunction, Förster resonance energy transfer (FRET), and liquid-junction dye-sensitized solar cells (DSSCs).
    Journal of Nanotechnology 01/2012; 2012.
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    ABSTRACT: Using a rapid microwave-assisted solvothermal approach ultrafine Ptnanoparticles 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 Ptnanoparticle sizes. The Pt-nanoparticle/TiO2nanotube 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 TiO2nanotube 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 oxidenanoparticles within a variety of nanotubular or nanoporous material systems with the resulting nanocomposites useful in catalysis, photocatalysis, photovoltaic, and photoelectrochemical applications.
    Journal of Materials Chemistry 08/2011; 21(35):13429-13433. · 5.97 Impact Factor
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    ABSTRACT: Photocorrosion stable WO(3) nanowire arrays are synthesized by a solvothermal technique on fluorine-doped tin oxide coated glass. WO(3) morphologies of hexagonal and monoclinic structure, ranging from nanowire to nanoflake arrays, are tailored by adjusting solution composition with growth along the (001) direction. Photoelectrochemical measurements of illustrative films show incident photon-to-current conversion efficiencies higher than 60% at 400 nm with a photocurrent of 1.43 mA/cm(2) under AM 1.5G illumination. Our solvothermal film growth technique offers an exciting opportunity for growth of one-dimensional metal oxide nanostructures with practical application in photoelectrochemical energy conversion.
    Nano Letters 01/2011; 11(1):203-8. · 13.03 Impact Factor
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    ABSTRACT: Tantalum nitride (Ta3N5) has a band gap of approximately 2.07 eV, suitable for collecting more than 45% of the incident solar spectrum energy. We describe a simple method for scale fabrication of highly oriented Ta3N5 nanotube array films, by anodization of tantalum foil to achieve vertically oriented tantalum oxide nanotube arrays followed by a 700 degrees C ammonia anneal for sample crystallization and nitridation. The thin walled amorphous nanotube array structure enables transformation from tantalum oxide to Ta3N5 to occur at relatively low temperatures, while high-temperature annealing related structural aggregation that commonly occurs in particle films is avoided. In 1 M KOH solution, under AM 1.5 illumination with 0.5 V dc bias typical sample (nanotube length approximately 240 nm, wall thickness approximately 7 nm) visible light incident photon conversion efficiencies (IPCE) as high as 5.3% were obtained. The enhanced visible light activity in combination with the ordered one-dimensional nanoarchitecture makes Ta3N5 nanotube arrays films a promising candidate for visible light water photoelectrolysis.
    Nano Letters 10/2010; · 13.03 Impact Factor
  • Angewandte Chemie International Edition 09/2009; 48(43):8095-8. · 11.34 Impact Factor
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    ABSTRACT: Modern excitonic solar cells efficiently harvest photons in the 350-650 nm spectral range; however, device efficiencies are typically limited by poor quantum yields for red and near-infrared photons. Using Forster-type resonance energy transfer from zinc phthalocyanine donor molecules to ruthenium polypyridine complex acceptors, we demonstrate a four-fold increase in quantum yields for red photons in dye-sensitized nanowire array solar cells. The dissolved donor and surface anchored acceptor molecules are not tethered to each other, through either a direct chemical bond or a covalent linker layer. The spatial confinement of the electrolyte imposed by the wire-to-wire spacing of the close-packed nanowire array architecture ensures that the distances between a significant fraction of donors and acceptors are within a Förster radius. The critical distance for energy transfer from an isolated donor chromophore to a self-assembled monolayer of acceptors on a plane follows the inverse fourth power instead of the inverse sixth power relation. Consequently, we observe near quantitative energy transfer efficiencies in our devices. Our results represent a new design paradigm in excitonic solar cells and show it is possible to more closely match the spectral response of the device to the AM 1.5 solar spectrum through use of electronic energy transfer.
    ACS Nano 04/2009; 3(4):788-94. · 12.03 Impact Factor
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    ABSTRACT: The goal of current dental and orthopedic biomaterials research is to design implants that induce controlled and guided tissue growth, and rapid healing. In addition to acceleration of normal wound healing phenomena, these implants should result in the formation of a characteristic interfacial layer with adequate biomechanical properties. To achieve these goals, however, a better understanding of events at the bone-material interface is needed, as well as the development of new materials and approaches that promote osseointegration. Here we present novel nanostructured nanoarrays from tantala that can promote cell adhesion and differentiation. Our results suggest that tantala nanotube arrays enhance osteoblast cell adhesion, proliferation and differentiation. The routes of fabrication of tantala nanotube arrays are flexible and cost-effective, enabling realization of desired platform topologies on existing non-planar orthopedic implants.
    Nanotechnology 02/2009; 20(4):045102. · 3.84 Impact Factor
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    ABSTRACT: We report on the self-assembled fabrication and photoelectrochemical properties of α-Fe2O3 (hematite) nanotube arrays, prepared by potentiostatic anodization of iron foil in an ethylene glycol electrolyte containing NH4F and deionized water. Vertically oriented nanotube arrays provide a highly ordered material architecture of high surface area that is nearly ideal for efficient transport and separation of photogenerated charges. We have achieved iron oxide nanotube arrays over a potential range of 30−60 V, using an electrolyte comprised of 0.2−0.5 wt % NH4F, and 2−4% DI water. The resulting nanotube arrays have a pore diameter ranging between 30 and 80 nm, with a minimum wall thickness of 10 nm. Nanotube formation is strongly dependent on the anodization bath temperature and fluoride concentration, with higher temperatures leading to increased rates of nanotube array growth, and with lower temperatures required in order to obtain identifiable nanotubes arrays for increased F− ion concentration. Crystallization of the as-synthesized, amorphous, iron oxide nanotube arrays to hematite is achieved through annealing in an oxygen-deficient ambient.
    Journal of Physical Chemistry C - J PHYS CHEM C. 01/2009; 113(36):16293-16298.
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    ABSTRACT: In this article, we present recent advances that we have achieved toward improving the properties of anodically formed semiconducting TiO 2 nanotubes as well as nanowire arrays as electrodes for oxidative photoelectro-chemistry. The morphology, crystallinity, composition, and illumination geometry of nanotube or nanowire arrays are critical factors in their performance as photoelectrodes. We discuss the key aspects relating to each factor and the advances achieved in improving each. With respect to the more fully investigated nanotube arrays, the ability to control the morphological parameters such as pore size, tube length, and wall thickness of the nanotube architecture has enabled high performance in applications such as water photoelectrolysis, photocatalysis, dye-sensitized solar cells, and heterojunction TiO 2 -polymer hybrid solar cells. We begin by reviewing the photoelectrochemical performance of state-of-the-art nanotube arrays fabricated on planar substrates. We then present more recent results related to the growth of TiO 2 nanotube arrays on nonplanar substrates designed in such a way that reflected light normally lost to free space is instead directed to a different point on the device, in turn improving overall photoconversion efficiency. Insofar as the crystallinity of the nanotubes is concerned, the use of a high-temperature oxygen or air-ambient anneal to crystallize the nanotube arrays is disadvantageous, since it results in a thick barrier layer where recombination losses occur and also because it precludes compatibility with polymeric substrates. In this regard, we discovered a two-step fabrication process for synthesis of crystallized nanotube arrays at low-temperatures. The photoelectro-chemical applications of TiO 2 are limited by its large electronic band gap. We briefly review the cationic and anionic doping approaches popularly used to modify the TiO 2 band gap. We consider the use of ternary oxide systems containing titania as both a structural support and corrosion-inhibitor, in particular fabrication and performance of n-type Ti-Fe-O nanotubes and p-type copper-rich Cu-Ti-O nanotubes, with a note on our recent synthesis of iron oxide nanotube arrays by anodic oxidation of iron. Fabrication and photoelec-trochemical properties of CdS-TiO 2 and CdTe-TiO 2 nanotube array heterojunction photoelectrodes are discussed. The article concludes by examining low temperature synthesis, and resulting properties, of single crystal vertically oriented TiO 2 nanowire arrays on transparent conductive glass substrates; preliminary investigation of these nanowire array photoelectrodes for water photolysis reveals them to have low series resistance and provide excellent separation of photogenerated charges.
    The Journal of Physical Chemistry C 01/2009; · 4.84 Impact Factor
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    ABSTRACT: Single-crystal one-dimensional (1D) semiconductor architectures are important in materials-based applications requiring a large surface area, morphological control, and superior charge transport. Titania has widespread utility in applications including photocatalysis, photochromism, photovoltaics, and gas sensors. While considerable efforts have focused on the preparation of 1D TiO2, no methods have been available to grow crystalline nanowire arrays directly onto transparent conducting oxide (TCO) substrates, greatly limiting the performance of TiO2 photoelectrochemical devices. Herein, we present a straightforward low temperature method to prepare single crystal rutile TiO2 nanowire arrays up to 5 microm long on TCO glass via a non-polar solvent/hydrophilic substrate interfacial reaction under mild hydrothermal conditions. The as-prepared densely packed nanowires grow vertically oriented from the TCO glass substrate along the (110) crystal plane with a preferred (001) orientation. In a dye sensitized solar cell, N719 dye, using TiO2 nanowire arrays 2-3 microm long we achieve an AM 1.5 photoconversion efficiency of 5.02%.
    Nano Letters 12/2008; 8(11):3781-6. · 13.03 Impact Factor
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    ABSTRACT: Lipoprotein particles are the main carriers of cholesterol in human blood circulation and play a key role in cholesterol transfer and metabolism. Recognition of the importance of cholesterol as a strong risk factor for coronary artery diseases has resulted in great interest in means to rapidly, and accurately, quantify lipoprotein fractions in the blood stream. This work presents a novel bio-sensing platform based on magnetoelastic resonance sensors for the detection of lipoprotein particles. The measurement is based on the selective bio-chemical reaction between a precipitator (dextran sulfate sodium salt and divalent metal Mg2+) and lipoproteins, producing insoluble precipitate which deposit onto the sensor surface, resulting in a change in the sensor resonance amplitude. The sensors show approximately a 20% change in resonance amplitude in a 10 mg/dl low density lipoprotein (LDL) solution, and an approximate 4% amplitude change in a high density lipoprotein (HDL) solution of the same concentration. Our results demonstrate that magnetoelastic sensors are suitable for selective detection of both LDL and HDL.
    Sensor Letters 05/2008; 6(3):359-362. · 0.52 Impact Factor
  • Xinjian Feng, Somnath C Roy, Craig A Grimes
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    ABSTRACT: Air bubbles are known to form at the liquid/solid interface of hydrophobic materials upon immersion in a liquid (Holmberg, M.; Kdühle, A.; Garnaes, J.; Mørch, K. A.; Boisen, A. Langmuir 2003, 19, 10510-10513). In the case of gravimetric sensors, air bubbles that randomly form at the liquid-solid interface result in poor sensor-to-sensor reproducibility. Herein a superhydrophilic ZnO nanorod film is applied to the originally hydrophobic surface of a resonance-based magnetoelastic sensor. The superhydrophilic coating results in the liquid completely spreading across the surface, removing unwanted air bubbles from the liquid/sensor interface. The resonance amplitude of uncoated (bare) and ZnO-modified sensors are measured in air and then when immersed in saline solution, ethylene glycol, or bovine blood. In comparison to the bare, hydrophobic sensors, we find that the standard deviation of the resonance amplitudes of the liquid-immersed ZnO-nanorod-modified sensors decreases substantially, ranging from a 27% decrease for bovine blood to a 67% decrease for saline. The strategy of using a superhydrophilic coating can be applied to other systems having similar interfacial problems.
    Langmuir 05/2008; 24(8):3918-21. · 4.38 Impact Factor

Publication Stats

358 Citations
99.70 Total Impact Points

Institutions

  • 2008–2012
    • Pennsylvania State University
      • • Department of Chemistry
      • • Materials Research Institute
      • • Department of Electrical Engineering
      University Park, MD, United States
  • 2011
    • Xi'an Jiaotong University
      • State Key Laboratory of Multiphase Flow in Power Engineering
      Xi’an, Shaanxi Sheng, China