Preparation And Gas Sensing Properties Of SnO₂/rGO Coated Fabric

Industrial and agricultural production and automobile exhaust emissions produce large amounts of NH₃,which,as a toxic and irritating gas,can cause damage to the human respiratory system,skin,and eyes when exposed to NH₃ atmosphere over 25 ppm for a long time;in addition,ammonia is present in human exhaled gas and is an important physiological indicator.With the continuous development of gas sensors and flexible electronic devices,researchers have turned their attention to flexible gas sensors that can detect the gases to be measured in real time at room temperature.SnO₂ is an important component of gas sensing materials due to its high sensitivity response to a variety of gases.To reduce the operating temperature of SnO₂,scholars have conducted research in reducing the grain size,designing low-dimensional nanostructures,and designing SnO₂composite sensing materials.Reduced graphene oxide（rGO）has excellent electrical conductivity and chemical stability,and its composite with SnO₂ can greatly reduce the resistance of the sensor,which can improve the gas sensing performance to a certain extent and realize gas detection at room temperature.Currently,flexible gas sensors are generally prepared by depositing the pre-prepared sensing material on the surface of the flexible substrate in the form of physical adsorption to form a film,which is prone to wear and peeling in the process of use.In this paper,we propose a novel method for the preparation of flexible gas sensors,in which a stable multilayer film is formed on the surface of pretreated polyimide fabric by layer self-assembly with the help of electrostatic attraction between Sn⁴⁺and GO,and then a hydrothermal method is used to nucleate and reduce Sn⁴⁺and GO in situ on the fabric surface to obtain a SnO₂/rGO composite coated fabric,in order to obtain uniformly dispersed small particle size SnO₂（3 nm）,and enhance the interaction between SnO₂ and rGO as well as the solidity of the coating.The main contents and conclusions of the paper are as follows.（1）Sn⁴⁺and GO were coated on the surface of pretreated polyimide（PI）fabric by electrostatic layer-by-layer self-assembly,and the SnO₂/rGO composite coating was obtained by in situ hydrothermal growth on the fabric surface.The morphological structure,electrical conductivity and ammonia sensing properties of the samples under different experimental conditions were characterized by Raman spectroscopy,scanning electron microscopy,X-ray diffractometer and static gas testing system.The results showed that the PI-SnO₂/rGO produced at a Sn⁴⁺/GO concentration ratio of 100(m M/mg·m L^-1)had the highest sensitivity to 200 ppm ammonia gas at room temperature by cyclically coating Sn⁴⁺and GO on the PI surface five times and reacting in a hydrothermal kettle at 180°C for 16 h.The SnO₂ nanoparticles in the composite coating were uniformly dispersed with a particle size of about 3 nm.As the initial GO oxidation decreased,then the SnO₂ nanoparticle particle size increased slightly and the interaction between SnO₂ NPs and rGO weakened.（2）The ammonia sensing performance of the composite coated fabric prepared by optimal process conditions was tested at room temperature.PI-SnO₂/rGO exhibited n-type sensing with a fast response value of 5.16%for 100 ppm NH₃（94 s/57 s）;the sensor showed a good linear response（R~2=0.995）for the detection of 50-400 ppm NH₃.The response value of the sensor for ammonia is also higher than that of the interfering line gas,with good selectivity;the device shows good continuous measurement repeatability and long-term stability;the fabric sensor has good stability with a sensitivity change rate of less than 5%under different humidity conditions（42%～65%）;the sensitivity loss is only 3%after 2000 times of stretching of the composite coated fabric by the micro tensionmeter,showing excellent resistance to mechanical deformation resistance.As the initial GO oxidation level decreases,PI-SnO₂/rGO*shows p-type sensing,with a response value of 11.3%for100 ppm NH₃ and a long response and recovery time（1000 s/267 s）,which is mainly attributed to the change of the NH₃ molecular action site,with NH₃ shifting from the SnO₂ surface to contact with the rGO sheets surface,and a weakened charge transfer between SnO₂ and rGO.The charge transfer between SnO₂ and rGO is weakened.The essay provides a new fabric-based gas sensor preparation method,which is simple and controllable,and the sensor exhibits good stability,and this method can be promoted in the fields of flexible gas sensors and wearable electronic devices.