Synthesis Of Tungsten Oxides Nanostructures And Their Gas Sensing Property

The conversion, storage, and utilization of renewable energy have all become more important than ever before as a response to ever-growing energy and environment concerns. The performance of energy-related technologies strongly relies on the structure and property of the material used. Various materials including metals, metal chalcogenides, oxides, carbides, nitrides, and phosphides have been developed, and tungsten oxides receives considerable attention in photocatalysis, gas sensors, electrochemistry, and phototherapy due to their unique physicochemical properties. In this paper, tungsten oxide nanomaterials with various morphology and chemical composition were synthesized by using hydrothermal and two-phase solvothermal methods: WO₃ nanorod bundles, WO₃-x nanowires and WO₃-x/GO composite. Furthermore, we have studied the gas-sensing properties of the as-obtained tungsten oxides. The main results and conclusions are as follows:Firstly, WO₃ products with various morphology were hydrothermal synthesized by using Na₂SO₄ as a directing agent of crystal growth. By altering the amount of Na₂SO₄, different morphology and sizes of WO₃ nanorods can be achieved. The effects of Na₂SO₄ concentration on the morphology, crystal phase of the obtained products were also investigated. Furthermore, the gas sensing properties of WO₃ nanorods were investigated in detail, respectively. Compared with other samples, the WO₃ nanorod bundles-based sensor exhibits a significantly better sensing performance（100 ppm formic acid, R a/R g=51.3）. Furthermore, it also possesses a good selectivity among various interfering gases.Secondly, we thus report that ultrathin nonstoichiometric tungsten oxide nanowires（WO₃-x） were successfully prepared through a simple one-pot two-phase strategy by employing sodium tungsten as tungsten source. Moreover, the nanowires with diameter of 2-3 nm and aspect ratios more than 100 exhibited excellent sensing performance（10 ppm NO2, R g/R a=56.0） toward NO2 at low temperature（100 o C）. We also investigate the influence of factors such as p H value and oleylamine amount in reaction system. The findings imply that appropriate p H value and the amount of oleylamine are the key factors to form ultrathin tungsten oxide nanowires.Finally, nonstoichiometric WO₃-x/GO composites with various morphology were two-phase solvothermal synthesized by using GO as a carrier and directing agent of crystal growth. By altering the reflux temperature, different morphology and sizes of WO₃-x/GO composites can be achieved. Furthermore, the gas-sensing properties of the as-prepared WO₃-x/GO composites were tested to NO2 gas. The stellate WO₃-x/GO composite with smaller particle size displays excellent gas-sensing performance in comparison to the other samples.