Room-temperature Ammonia-Sensing Properties Of The Polyaniline-Based Nanocomposites Modified With WO₃ Nanoplates And Carbon Nanotubes

With the rapid progress of technologies and the society,people are paying more and more attention to the problem of air quality,which leads to the new demand of gas sensors.However,the working temperatures of the gas sensors commercially available now are generally high,increasing the cost of sensors,and leading to potential dangers in the conditions containing flammable and combustible substances.Therefore,it is urgent to develop gas sensors that can work at room temperature??25^oC?.This work starts from the design of sensing materials focusing on the conductive polymer of polyaniline?PANI?with reversible doping characteristics,to synthesize WO3@PANI and CNT@PANI nanocomposites with hierarchical interface structures to improve their room-temperature gas-sensing performance towards NH₃.The chemical compositions and microstructures of the samples were characterized by various methods.Their ammonia sensing behavior and relative mechanism were systematically studied.The main research contents of this paper are as follows:?1?Preparation,characterization and gas-sensing properties of WO₃ nanoplates modified polyaniline?WO3@PANI?nanocomposites.WO₃ nanoplates were firstly prepared by the intercalation and topochemical conversion process with commercial tungstic acid as the raw material.The SEM and TEM results show that the thickness of the as-prepared WO₃ nanoplates was a few nanometers.The WO₃@PANI nanocomposites were then prepared by growing PANI nanoparticles on the surface of the WO₃ nanoplates via an ultrasonic spray assisted in-situ polymerization method?UWP?.The characterization results showed that the WO₃@PANI composite has a hierarchical structure which is beneficial to electron transport and gas adsorption.The addition amount of WO₃ nanoplates has an obvious impact on their ammonia-sensing properties.When the molar ratio of aniline monomers to WO₃ nanoplates was 2.5,the as-obtained WO₃@PANI sample of UWP-2.5 exhibits the highest ammonia-sensing properties:the response to 100 ppm ammonia at room temperature is up to 34,which is about 10 times higher than PANI.It also shows a good repeatability,selectivity,long-term stability and low theoretical detection limit?3 ppb?.The enhanced gas-sensing properties can be mainly due to the hierarchical structure and the p-n heterojunction between WO₃ and PANI.In addition,the comparative study between the conventional in-situ polymerization method?TWP?and UWP indicates that the ultrasonic spray method is beneficial to the control of the microstructure of the WO₃@PANI composites,thus improving their the ammonia-sensing performance.?2?Preparation,characterization and gas-sensing properties of carbon nanotubes modified polyaniline?CNT@PANI?nanocomposites.The CNT@PANI nanocomposites were prepared using the ultrasonic spary-assisted in-situ polymerization method.For the preparation of CNT@PANI nanocomposites,carbon nanotubes were acidified to produce the functional groups such as hydroxyl group and carboxyl group on their surfaces;aniline molecules were then added to the suspension containing acid-treating carbon nanotubes,and the oxidizing agent ammonium persulfate via the ultrasonic spray process.The CNT@PANI nanocomposites with different amounts of carbon nanotubes were synthesized to check the effect of carbon nanotubes on their ammonia-sensing performance.Gas-sensing performance tests show that the content of carbon nanotubes plays an important role in their gas-sensing properties.The CNT@PANI sample?PC-1%?with a mass ratio of 1%of CNT to aniline exhibits the highest response of 5 upon exposure to 50 ppm ammonia,which is much higher than PANI or carbon nanotubes.The response time of PC-1%to 50 ppm ammonia is 27 s,as PANI was 135 s at the same conditions.The synergistic effect between CNTs and PANI,the excellent electronic transmission property of CNTs and the crosslinked network structure of CNT@PANI nanocomposites are the main reasons for their improvement in ammonia-sensing performance.