Solvothermal, chloroalkoxide-based synthesis of monoclinic WO(3) quantum dots and gas-sensing enhancement by surface oxygen vacancies.

We report for the first time the synthesis of monoclinic WO3 quantum dots. A solvothermal processing at 250 °C in oleic acid of W chloroalkoxide solutions was employed. It was shown that the bulk monoclinic crystallographic phase is the stable one even for the nanosized regime (mean size 4 nm). The nanocrystals were characterized by X-ray diffraction, High resolution transmission electron microscopy, X-ray photoelectron spectroscopy, UV-vis, Fourier transform infrared and Raman spectroscopy. It was concluded that they were constituted by a core of monoclinic WO3, surface covered by unstable W(V) species, slowly oxidized upon standing in room conditions. The WO3 nanocrystals could be easily processed to prepare gas-sensing devices, without any phase transition up to at least 500 °C. The devices displayed remarkable response to both oxidizing (nitrogen dioxide) and reducing (ethanol) gases in concentrations ranging from 1 to 5 ppm and from 100 to 500 ppm, at low operating temperatures of 100 and 200 °C, respectively. The analysis of the electrical data showed that the nanocrystals were characterized by reduced surfaces, which enhanced both nitrogen dioxide adsorption and oxygen ionosorption, the latter resulting in enhanced ethanol decomposition kinetics.

[1]  Zhigang Zhao,et al.  Single‐Crystalline Tungsten Oxide Quantum Dots for Fast Pseudocapacitor and Electrochromic Applications , 2014, Advanced materials.

[2]  J. M. Rosolen,et al.  Self-assembled films from WO3: Electrochromism and lithium ion diffusion , 2010 .

[3]  J. Cheon,et al.  In situ one-pot synthesis of 1-dimensional transition metal oxide nanocrystals. , 2005, The journal of physical chemistry. B.

[4]  Xiaohong Sun,et al.  Morphology, phase structure and acetone sensitive properties of copper-doped tungsten oxide sensors , 2014 .

[5]  Zhifu Liu,et al.  Preparation of WO3 nanoparticles and application to NO2 sensor , 2009 .

[6]  C. Liu,et al.  Low-temperature hydrothermal synthesis of WO3 nanorods and their sensing properties for NO2 , 2012 .

[7]  E. Fortunato,et al.  Microstructure control of dual-phase inkjet-printed a-WO3/TiO2/WOX films for high-performance electrochromic applications , 2012 .

[8]  Jiaguo Yu,et al.  Spontaneous formation of a tungsten trioxide sphere-in-shell superstructure by chemically induced self-transformation. , 2008, Small.

[9]  Pedro Barquinha,et al.  WO3 nanoparticle-based conformable pH sensor. , 2014, ACS applied materials & interfaces.

[10]  E. Cuéllar,et al.  Photocatalytic properties of WO3 nanoparticles obtained by precipitation in presence of urea as complexing agent , 2011 .

[11]  Qiang Ma,et al.  Ultrathin W18O49 nanowires with diameters below 1 nm: synthesis, near-infrared absorption, photoluminescence, and photochemical reduction of carbon dioxide. , 2012, Angewandte Chemie.

[12]  Shih‐Yuan Lu,et al.  Dispersing WO3 in carbon aerogel makes an outstanding supercapacitor electrode material , 2014 .

[13]  G. Lu,et al.  Flower-like WO3 architectures synthesized via a microwave-assisted method and their gas sensing properties , 2013 .

[14]  Yuxiang Qin,et al.  Solvothermally synthesized tungsten oxide nanowires/nanorods for NO2 gas sensor applications , 2011 .

[15]  Zhimin Liu,et al.  One-pot solvothermal method to synthesize platinum/W18O49 ultrafine nanowires and their catalytic performance , 2012 .

[16]  A. Shpak,et al.  XPS studies of active elements surface of gas sensors based on WO3−x nanoparticles , 2007 .

[17]  A. Galeckas,et al.  One-dimensional WO3 and its hydrate: One-step synthesis, structural and spectroscopic characterization , 2012 .

[18]  Tao He,et al.  Photochromic materials based on tungsten oxide , 2007 .

[19]  Kengo Shimanoe,et al.  Theory of power laws for semiconductor gas sensors , 2008 .

[20]  G. Niklasson,et al.  Electronic and optical properties of nanocrystalline WO3 thin films studied by optical spectroscopy and density functional calculations , 2013, Journal of physics. Condensed matter : an Institute of Physics journal.

[21]  Jing Sun,et al.  Effects of morphologies on acetone-sensing properties of tungsten trioxide nanocrystals , 2011 .

[22]  Yue Zhang,et al.  Chemical and structural analysis of solvothermal synthesized tungsten oxide nanotube without template and its hydrogen sensitive property , 2014 .

[23]  A. J. McQuillan,et al.  Attenuated total reflection infrared studies of oleate and trioctylphosphine oxide ligand adsorption and exchange reactions on CdS quantum dot films. , 2008, Langmuir : the ACS journal of surfaces and colloids.

[24]  M. Antonietti,et al.  Growth and assembly of crystalline tungsten oxide nanostructures assisted by bioligation. , 2005, Journal of the American Chemical Society.

[25]  Yu Wang,et al.  The enhanced alcohol-sensing response of ultrathin WO3 nanoplates , 2010, Nanotechnology.

[26]  T. D. Senguttuvan,et al.  Gas sensing properties of nanocrystalline tungsten oxide synthesized by acid precipitation method , 2010 .

[27]  R. Figueroa,et al.  WO3 pillar-type and helical-type thin film structures to be used in microbatteries , 2007 .

[28]  D. A. Edwards,et al.  890. Halide and oxyhalide complexes of molybdenum and tungsten , 1963 .

[29]  Xiaoheng Liu,et al.  Synthesis, characterization and enhanced gas sensing performance of WO3 nanotube bundles , 2013 .

[30]  Xiaoming Sun,et al.  Highly sensitive WO3 hollow-sphere gas sensors. , 2004, Inorganic chemistry.

[31]  Bernard Desbat,et al.  Infrared and Raman study of WO3 tungsten trioxides and WO3, xH2O tungsten trioxide tydrates , 1987 .

[32]  Olgierd J. Klejnot.  Chloride alkoxides of pentavalent tungsten. , 1965 .

[33]  Pietro Siciliano,et al.  Chloro-Alkoxide Route to Transition Metal Oxides. Synthesis of WO3 Thin Films and Powders from a Tungsten Chloro-Methoxide , 2009 .

[34]  Xiaogang Peng,et al.  Formation and stability of size-, shape-, and structure-controlled CdTe nanocrystals: Ligand effects on monomers and nanocrystals , 2003 .

[35]  G. Lu,et al.  Ultrasensitive and low operating temperature NO2 gas sensor using nanosheets assembled hierarchical WO3 hollow microspheres , 2012 .

[36]  N. Sharpless,et al.  Electron Spin Resonance Study of Some Halomolybdenyl, -tungstenyl, and -vanadyl Complexes in Solution , 1966 .

[37]  J. Madarász,et al.  Gas sensing selectivity of hexagonal and monoclinic WO3 to H2S , 2010 .

[38]  R. Hayn,et al.  Mechanism of CO and O3 sensing on WO3 surfaces: First principle study , 2011 .

[39]  Claes-Göran Granqvist,et al.  Electrochromic tungsten oxide films: Review of progress 1993–1998 , 2000 .

[40]  Wojtek Wlodarski,et al.  Facile synthesis of nanostructured WO3 thin films and their characterization for ethanol sensing , 2013 .

[41]  Arnan Mitchell,et al.  Nanostructured Tungsten Oxide – Properties, Synthesis, and Applications , 2011 .

[42]  D. Kohl.  Surface processes in the detection of reducing gases with SnO2-based devices , 1989 .

[43]  Jinhuai Liu,et al.  Large-scale synthesis of hydrated tungsten oxide 3D architectures by a simple chemical solution route and their gas-sensing properties , 2011 .

[44]  Jun Zhang,et al.  Pt clusters supported on WO3 for ethanol detection , 2010 .

[45]  Satyen K. Deb,et al.  Opportunities and challenges in science and technology of WO3 for electrochromic and related applications , 2008 .

[46]  Z. Yamani,et al.  Synthesis of highly active nanocrystalline WO3 and its application in laser-induced photocatalytic removal of a dye from water , 2009 .

[47]  W. Guo,et al.  Hydrothermal synthesis of assembled sphere-like WO3 architectures and their gas-sensing properties , 2012 .

[48]  Yuxiang Qin,et al.  Synthesis and NO2-sensing properties of one-dimensional tungsten oxide nanowire bundles , 2011, 2010 3rd International Nanoelectronics Conference (INEC).

[49]  B. Miao,et al.  Hydrothermal synthesis and gas sensing properties of WO3H2O with different morphologies , 2014 .

[50]  Geyu Lu,et al.  Highly sensitive NO2 sensor based on square-like tungsten oxide prepared with hydrothermal treatment , 2011 .

[51]  P. P. Sahay,et al.  Structural and alcohol response characteristics of Sn-doped WO3 nanosheets , 2014 .

[52]  Eduard Llobet,et al.  Au nanoparticle-functionalised WO3 nanoneedles and their application in high sensitivity gas sensor devices. , 2011, Chemical communications.

[53]  N. Hoa,et al.  Gas nanosensor design packages based on tungsten oxide: mesocages, hollow spheres, and nanowires , 2011, Nanotechnology.

[54]  Xintai Su,et al.  In situ etching WO3 nanoplates: Hydrothermal synthesis, photoluminescence and gas sensor properties , 2010 .

[55]  Yuxiang Qin,et al.  Effect of annealing on microstructure and NO2-sensing properties of tungsten oxide nanowires synthesized by solvothermal method , 2011 .

[56]  D. Lee,et al.  FTIR spectral characterization of thin film coatings of oleic acid on glasses: I. Coatings on glasses from ethyl alcohol , 1999 .

[57]  J. Augustynski,et al.  Crystallographically oriented mesoporous WO3 films: synthesis, characterization, and applications. , 2001, Journal of the American Chemical Society.

[58]  N. Bârsan,et al.  Template‐Free Synthesis and Assembly of Single‐Crystalline Tungsten Oxide Nanowires and Their Gas‐Sensing Properties. , 2006 .

[59]  Kent J. Bradford,et al.  Structure and Composition , 2013 .

[60]  R. Hayn,et al.  Mechanism of NOx sensing on WO3 surface: First principle calculations , 2014 .

[61]  P. Judeinstein,et al.  Sol–gel synthesis of WO3 thin films , 1991 .

[62]  Zhifu Liu,et al.  Facile synthesis and NO2 gas sensing of tungsten oxide nanorods assembled microspheres , 2009 .

[63]  W. Seo,et al.  Synthesis and optical properties of colloidal tungsten oxide nanorods. , 2003, Journal of the American Chemical Society.

[64]  Jordi Arbiol,et al.  NH3 interaction with chromium-doped WO3 nanocrystalline powders for gas sensing applications , 2004 .

[65]  Application of organic supramolecular and polymeric compounds for chemical sensors , 1994 .

[66]  E. Cuéllar,et al.  Synthesis and characterization of WO3 nanoparticles prepared by the precipitation method: Evaluation of photocatalytic activity under vis-irradiation , 2010 .

[67]  M. Miyauchi,et al.  Nanoporous-walled tungsten oxide nanotubes as highly active visible-light-driven photocatalysts. , 2008, Angewandte Chemie.

[68]  Do Kyung Kim,et al.  Solvothermal Synthesis of Tungsten Oxide Nanorod/Nanowire/Nanosheet , 2005 .

[69]  Songhun Yoon,et al.  Development of high-performance supercapacitor electrodes using novel ordered mesoporous tungsten oxide materials with high electrical conductivity. , 2011, Chemical communications.

[70]  S. Contarini,et al.  Ion-beam-induced chemical changes in the oxyanions (Moyn-) and oxides (Mox) where M = chromium, molybdenum, tungsten, vanadium, niobium and tantalum , 1987 .

[71]  G. Sberveglieri,et al.  Structural and gas-sensing characterization of tungsten oxide nanorods and nanoparticles , 2011 .

[72]  H. Meng,et al.  XPS studies on surface reduction of tungsten oxide nanowire film by Ar+ bombardment , 2012 .

[73]  E. Salje.  Lattice dynamics of WO3 , 1975 .

[74]  Z. Fu,et al.  Nanostructured WO3 thin film as a new anode material for lithium-ion batteries , 2010 .

[75]  Zhong Lin Wang,et al.  Three-dimensional WO3 nanostructures on carbon paper: photoelectrochemical property and visible light driven photocatalysis. , 2011, Chemical communications.

[76]  N. Vuong,et al.  Realization of an open space ensemble for nanowires: a strategy for the maximum response in resistive sensors , 2012 .

[77]  M. Leskelä,et al.  WO3 photocatalysts: Influence of structure and composition , 2012 .

[78]  Pelagia-Irene Gouma,et al.  Synthesis and Sensing Properties to NH3 of Hexagonal WO3 Metastable Nanopowders , 2007 .

[79]  Nicolae Barsan,et al.  Synthesis, Mechanism, and Gas‐Sensing Application of Surfactant Tailored Tungsten Oxide Nanostructures , 2009 .

[80]  N. Bârsan,et al.  Conduction Model of Metal Oxide Gas Sensors , 2001 .

[81]  Yuxiang Qin,et al.  Synthesis and NO 2 -sensing properties of one-dimensional tungsten oxide nanowire bundles , 2010 .