Preparation And Ammonia-sensing Properties Of Tungsten Oxide Nanorods Based Organic Core-shell Structure

With the development of the society,people are increasingly demanding the quality of living environment.It is imperative to monitor the outdoor atmosphere and indoor air quality in real time in order to avoid health hazards caused by gas pollution.Therefore,the development and application of gas sensors are receiving more and more attention.Metal oxide semiconductors are the ideal material of most of the traditional gas sensors.However,the inherent defects of metal oxide semiconductors-based gas sensors,such as high working temperature,poor gas selectivity makes them difficult to be widely used in large-scale industrial production,it is also difficult to meet the miniature and integrated applications of sensitive components.As a result,it is necessary to improve the room temperature gas sensitivity of metal oxide semiconductor materials.The aims of the study is preparing a kind of one-dimensional tungsten oxide-based organic core-shell gas sensor with high sensitivity and low detection limit to ammonia at room temperature.In this study,one-dimensional tungsten oxide nanorods was controllably prepared by solvothermal method,and then a ultra thin polypyrrole shell on the surface of tungsten oxide nanorods via a liquid-phase chemical oxidation polymerization method.Finally,a kind of PPy wrapped W₁₈O₄₉ core-shell structure was successfully prepared.The results of experiments show that the ammonia sensitivity of PPy@W₁₈O₄₉ core-shell nanorods is greatly dependent on the temperature.The optimum working temperature is 15^oC,and the sensitivity of ammonia gas declines sharply with the increase of working temperature,The anomalous p-n anti-type phenomenon appeared at the relative high temperature;the polypyrrole coating on the surface of W₁₈O₄₉ nanorods could effectively improve the ammonia sensitivity of W₁₈O₄₉ nanorods,and the thinner the polypyrrole shell,the more obvious optimize effect.The thin shell?5nm?PPy@W₁₈O₄₉ nanorods?15^oC?ammonia sensitivity detection limit can reach 1ppm,PPy@W₁₈O₄₉ nanorods sensor exhibit about 2.4 to 3.7 times response enhancement to 10²00ppm NH₃ gas compared to the pristine one.Further research found that?Ag-PPy?@W₁₈O₄₉ nanorods can be successfully prepared by the improvement of liquid-phase chemical oxidative polymerization method.This is the first reported one-step preparation of the shell structure while also achieving effective surface modification of precious metals in the field of preparation of low-dimensional organic shell core-shell material.The highest sensitivity of?Ag-PPy?@W₁₈O₄₉ nanorods with silver particle surface modification to 10-50ppm ammonia at room temperature?25^oC,³5%RH?is 2.11 times than PPy@W₁₈O₄₉nanorods with same shell thickness?5nm shell thickness?.The detection limit of the silver particle surface modificated core-shell structure?100ppb?is much less than that of PPy@W₁₈O₄₉ nanorodes sensors?5ppm?.