Preparation And Gas Sensitivity Of Plant Fiber Based Sensor

Gas sensors are mainly composed of sensing materials and sensing substrates.Ideal gas sensors generally need to meet such indicators as high sensitivity,good selectivity and fast response speed.The interaction between the target gas molecules and the sensing material mainly takes place on the surface of the sensing material,so the structural properties of the sensing material and the gas permeability of the sensing substrate are related to the detection performance of the sensor.The traditional sensing substrate,such as ceramics,has poor permeability and is difficult to degrade,which not only limits the gas sensing performance of the sensing material,but also easily produces solid waste.Therefore,this paper mainly studies the use of degradable and permeable plant fibers（filter paper and cotton cloth）as the sensing substrate,and the use of polyaniline（PANI）,a polymer with low cost and easy to control structure and performance,as the sensing material.Then,the gas sensing performance of PANI sensor is regulated from two aspects of sensing material and sensing substrate,focusing on the construction of plant fiber-based PANI gas sensor and scientific issues in the regulation of gas sensing performance,and comparing with traditional PANI gas sensor.The main work are as follows:（1）The flexible sensor based on flower-like polyaniline coated filter paper（PCFP）was developed by spraying for the first time.Hierarchical structure,high permeability of filter paper and the interaction between amino groups of PANI and nitro groups of nitroaromatic explosives contributed to the responses of PCFP to detection 2,4,6-trinitrotoluene（TNT）,picric acid（PA）and 2,4-dinitrotoluene（DNT）was 237.7,100.6 and 80.1%,respectively at room temperature.The average response time and recovery time to TNT,PA and DNT are no more than 8.1 and 1.9 s,respectively.The theoretical limit of detection for TNT and PA is 0.094 and 0.029 ppb,respectively.More importantly,the special interlaced flower-like structures of polyaniline contributed to the good flexural stability.The response fluctuation to TNT,PA and DNT decreases of responses are less than 7.9%after 2000 bends of 40^o.In addition,the spraying method is suitable for economical,efficient and large-scale preparation of paper-based flexible sensors.（2）Cotton fibers/polyaniline（PANI）composites were prepared acting as flexible sensors in order to avoid the waste brought by traditional sensing substrates.The uniform coating of PANI endowed the cotton strip loaded with PANI sensor（CSPS）and cotton yarn loaded with PANI sensor（CYPS）with good mechanical,electromagnetic shielding and gas sensing properties.Both CSPS and CYPS show high selectivity to NH₃,high resistance to humidity and good repeatability between sensors.Quasi-one-dimensional CYPS has a higher surface exposure rate.The response of CYPS to 100 ppm NH₃increased from CSPS（-32.1%）to-92.1%,and the recovery time was shortened from CSPS（30.1 s）to 20.1 s.The research has expanded cotton fibers application field.（3）Inspired by the enhanced gas sensing performances by the one-dimensional hierarchical,one-dimensional hierarchical polyaniline/multi-walled carbon nanotubes（PANI/CNT）fibers were prepared.Interestingly,the simple heating changed the sensing characteristics of PANI from p-type to n-type.The p-type PANI/CNT（p-PANI/CNT）and n-type PANI/CNT（n-PANI/CNT）performed the higher sensitivity to NO₂and NH₃,respectively.The response times of p-PANI/CNT and n-PANI/CNT to 50 ppm of NO₂and NH₃are only 5.2 and 1.8s,respectively,showing the real-time response.The estimated limit of detection for NO₂and NH₃is as low as to 16.7 and 6.4 ppb,respectively.After three months,the responses of p-PANI/CNT and n-PANI/CNT decreased by 19.1%and 11.3%,respectively.This work also looks forward to the development prospects of cost-effective,high-performance PANI/CNT-based sensors.