Core-shell structure of polypyrrole grown on W18O49 nanorods for high performance gas sensor operating at room temperature

In this work, uniform core-shell structure of polypyrrole wrapped on tungsten oxide nanorods (PPy@W18O49 core-shell nanorods) were synthesized via a two-step process for gas-sensing applications. The core-nanorods of W18O49 were first grown by solvothermal method with tungsten hexachloride (WCl6) as precursor. The PPy-shell layer was then formed uniformly on the solvothermally synthesized W18O49 nanorods by in-situ chemical polymerization of pyrrole monomer (Py), with sodium dodecyl benzene sulfonic acid (DBSA) as dopant and ammonium persulfate (APS) as oxidant. High dispersion of Py achieving in ethanol is proved to be crucial to form the uniform PPy-shell layer, and the layer thickness of PPy-shell is highly controlled by adjusting the Py concentration in polymeric solution. The morphology and structure of the nanocomposite were characterized systematically; it shows that the composite exhibits perfect core-shell structure of one-dimensional (1D) nanorods with average diameter of around 70-90 nm. The NH3-sensing properties of the sensors based on the PPy@W18O49 core-shell nanorods were investigated at operating temperature of 15-130 degrees C over NH3 concentration ranging from 1 to 200 ppm. The response magnitude of the PPy@W18O49 sensor can be affected seriously by temperature fluctuation, even in room temperature range (15-30 degrees C), and meanwhile, a temperaturedependent p-n response characteristic reversal is observed for the heteronanorods sensor. At much low room temperature of 15 degrees C, the present PPy@W18O49 nanorods show quick and sensitive response to NH3 gas mainly due to the ultrathin, uniform PPy shell and the special heterojunction effect between ptype PPy and n-type W18O49. The underlying gas-sensing mechanism is analyzed. (C) 2017 Elsevier B.V. All rights reserved.