Facile realization of Ag functionalized W₁₈O₄₉@PPy core–shell nanorods for multieffect modulation on gas sensing response

Surface modification and core–shell heterostructure are all proved effective in improving gas-response performance of a semiconductor sensor. Here Ag nanoparticles (Ag NPs) modified W₁₈O₄₉@PPy core–shell nanorods (Ag/CSNRs) prepared by a cost-effective process are investigated for enhanced NH₃-sensing response. In present process, surface modification by Ag NPs is achieved in parallel to the PPy-shell formation via chemical polymerization of Py on W₁₈O₄₉ nanorods with AgNO₃ as an oxidant. The distribution (partial or total embedding in PPy-shell) and amount of the modified Ag NPs are revealed to be decided by Py polymerization duration, and affect the gas response of corresponding Ag/CSNRs sensor. The sensor based on Ag/CSNRs exhibits significantly enhanced response. The sample modified with partially embedded Ag NPs is capable of detection to rarefied NH₃ as low as 100 ppb at room temperature. However, long duration of polymerization induces a full coverage of Ag NPs by PPy film and thus seriously weakens the modification effect to gas response. A sensing mechanism model was proposed and the response feature of Ag/CSNRs was analyzed with the perspective of co-contribution of chemical sensitization and electronic sensitization, which is further correlated to the distribution of attached Ag NPs.