Tungsten Oxides: Hydrothermal Fabrication And Properties

With the fast development of nanotechnology, nanomaterials exhibit a greatapplication prospect on promoting the development of science and technology, andameliorating the material life of human. Among various metal oxide nanomaterials,tungsten oxide nanostructures have received a widespread attention due to theirprominent physical and chemical properties, such as electrochromism, photocatalysis,gas sensing, and so on. Recent reports showed that, the materials have the promisingapplication in a vast area, such as gas sensor, smart window, photocatalysts, and soon. On the aspect of the fabrication of nanomaterials, hydrothermal method hasattained a general use owing to its economical apparatus, simple operation and easycontrolled experiment conditions.Herein, we report the hydrothermal fabrications of three tungsten oxides:WO₃·0.33H₂Onanoplates, WO₃nanoplates and W18O49nanowire networks by thecontrol of experiment temperature and the assisted agents. Further, the properties ofthe as-obtained tungsten oxides, including gas sensing, photocatalytic and absorptiveproperties, have been studied. The details are as follows:WO₃·0.33H₂Onanoplates：WO₃·0.33H₂Onanoplates have been synthesized withp-nitrobenzoic acid as a structure-directing agent through a facile hydrothermalmethod. The obtained products were characterized by X-ray diffraction （XRD） andscanning electron microscope （SEM）. The SEM results showed that most of theproducts had a hexagonal morphology with a lateral size of500–1000nm and athickness of⁸0nm. The XRD result showed that the products were orthorhombicWO₃·0.33H₂O: The photocatalytic and gas-sensing properties of the WO₃·0.33H₂Onanoplates were studied. The products exhibited a high degradation activity formethylene blue （MB） under ultraviolet light irradiation, and a high sensitivity tocyclohexene. The facile preparation method and the improved properties derived from the plate-shaped nanostructures are significant in the synthesis and futureapplications of functional nanomaterials.WO₃nanoplates: Triclinic WO₃nanoplates with prominent cyclohexene sensingand photocatalytic properties were fabricated via a facile hydrothermal methodassisted with p-aminobenzoic acid （PABA）. The as-prepared product wascharacterized by XRD, SEM and TEM, which illustrated that the WO₃nanoplateshave a triclinic phase with the length of100–200nm and the thickness of50–80nm.The gas sensing properties of the WO₃nanoplates were measured by detection ofmethanol, ethanol, cyclohexane, benzene, ethyl acetate and acetone at160–300oC,and their photocatalytic activities were investigated by the degradation of MB. Theas-prepared product exhibited not only excellent photocatalytic property for thedegradation of MB, but also high response （1000ppm of cyclohexene, Ra/Rg=140）and excellent selectivity for the detection of cyclohexene.W₁8O₄9nanowire networks: W18O49nanowire networks were fabrication thougha hydrothermal method with Na₂WO₄2H₂O as tungsten resource, tungsten acid asprecursor and PABA as a weak reductive and structure-directing agent. The role ofPABA has been discussed by the contrast experiments. Further, the water treatmentability of the W18O49nanowire networks has been investigated by the adsorption oforganic dyeing wastewater and heavy metal ion wastewater. Experimental data showsthat the products are efficient in the adsorption of MB (201mg·g^-1), RhB (120mg·g^-1)and Pb （II）(192mg·g^-1) due to their large special surface (223m²·g^-1).The above research demonstrated that the hydrothermal method is a prominentmeasure on the fabrication of tungsten oxide nanomaterials with differentmorphologies and components. A further performance estimates indicated that thetungsten oxide nanomaterials exhibit excellent physical and chemical properties,which have a potential application on gas sensors and waste-water treatment.