Research On The Design And The Gas Sensing Performance Of Ammonia Flexible Sensors Based On Polyaniline Nanocomposite

Ammonia（NH₃）is a common atmospheric pollutant that is colorless,irritating and corrosive.Human who inhales too much NH₃ is more likely to experience uremia,cirrhosis,and renal failure.In addition,NH₃ is a naturally occurring body product that is produced by a variety of metabolic activities,and it has the potential to be employed as a biomarker for kidney disorders.As a result,the design and preparation high-performance（high sensitivity,low detection limit,good stability）NH₃ sensor are of great research significance in the fields of environmental monitoring and medical diagnosis.Polyaniline（PANI）,a sensitive material with development potential in current NH₃ sensor research,is easy to prepare,has a large specific surface area and reversible doping and de-doping characteristics,etc.However,NH₃ sensors based on pure PANI generally suffer from low sensitivity,weak response/recovery speed and poor stability.In recent years,modulating the material shape and doping modification of PANI has proven to be an effective strategy for improving the gas-sensing performance of PANI-based NH₃ sensors.In this paper,the ternary nanocomposites were prepared utilizing titanium dioxide-gold nanoparticles（TiO₂-Au NPs）and gold@silicon dioxide nanoparticles（Au@SiO₂NPs）doped PANI,respectively,to construct flexible NH₃ sensors that can work at room temperature on polyimide（PI）substrates.Here,the research work was carried out in terms of sensitive material design,gas-sensing performance testing and sensing mechanism analysis.The details are as follows:（1）Considering that TiO₂ and Au nanoparticles（Au NPs）serve different work functions than PANI,the doping occurs energy band bending at the contact interface and forms p-n heterojunctions and Schottky junctions,which can improve PANI sensors’gas sensing capability.In this paper,an economical and practical ternary NH₃sensor was successfully prepared on PI substrate by compounding highly catalytically active Au NPs（controlled synthesis,particle size<100 nm）,n-type TiO₂（particle size<20 nm）and PANI using in situ chemical oxidation polymerization method,and the sensors were systematically characterized.The results indicated that the gas-sensing performance of the PANI sensor was significantly improved after Au and TiO₂ doping:the PANI-TiO₂-Au ternary sensor’s response and recovery time for 100 ppm NH₃ were32s and 111s,respectively,with a response value of 123%,which is approximately 1.9times and 1.2 times higher than the pure PANI and binary PANI-TiO₂;The designed ternary sensor showed favorable linearity（correlation coefficient R²=0.9984）in dry NH₃,which facilitates the measurement of NH₃ at ppm level in practical applications.（2）An effective strategy was presented in this research to improve the capability of PANI sensors to detect NH₃,in addition to employing typical n-type metal oxides to form heterojunctions with PANI.To develop high-performance flexible NH₃ sensors using innovative core-shell Au@SiO₂ NPs doped with PANI that combine the benefits of inorganic and organic components,and expe the doping effect of Au@SiO₂ on PANI.The results revealed that Au@SiO₂（20 wt%）doped PANI NH₃ sensor（PAS2）has excellent sensitivity,flexibility and stability at room temperature:The PAS2 sensor had a response value of 80%for 10 ppm NH₃,which was approximately 1.5 times higher than that the pure PANI sensor,and can detect ultra-low NH₃ concentrations of 10 ppb;the PAS2 sensor of concentration deviation（concentration deviation corresponding to response deviation）induced by bending angles（about-85 to 85 degrees）and cycle times（from 0 to 500 times）could be kept within 0.6 ppm;the deviation of PAS2 sensor response value was less than 2.7%for 30 days continuous monitoring.Additionally,the response value of the PAS2 sensor was insensitive to ambient humidity（48%-66%RH）.It is analyzed that the superior gas-sensing performance of PAS2 sensor was mainly attributed to Au@SiO₂ NPs.Here,the sensing mechanism model of the core-shell Au@SiO₂ NPs to enhance the gas-sensing performance of PANI sensor was established.