Research On Flexible Humidity Sensor Based On SnO₂/rGO Nanocomposites

Accurate detection and control of humidity has an important impact on both production development and human health.In recent years,researchers have not only continued to explore and develop new materials with higher performance,but also combined with flexible electronics to continuously expand the application range of humidity sensors.Tin dioxide(SnO2)and graphene have excellent physical and chemical properties and have been attracted many researchers to widely research.However,humidity sensors based on pure SnO2 have disadvantages such as high power consumption and poor stability.Graphene materials also have shortcomings such as low sensitivity to water molecules and long response time.In order to make up for the defects of a single material and enhance the sensing performance,the preparation of composites is an effective way.Nevertheless,there are few related studies on the influence of different doping ratios on the surface morphology and humidity sensitivity of composites.In addition,the influence of different sensitive film preparation methods on the application of flexible humidity sensors is also less discussed.Therefore,based on SnO2/rGO nanocomposites,we developed a flexible SnO2/rGO humidity sensor and explored the influence of different rGO doping ratios on humidity-sensitive properties of the nanocomposites.In addition,we analyzed the humidity performance of SnO2/rGO sensitive film which are prepared by the coating method and the electrospinning method,respectively.Finally,the application potential of the sensor in the field of human respiratory monitoring is explored.The main research work of this paper is as follo ws:(1)A one-step hydrothermal method was used to prepare SnO2/rGO nanocomposites with different rGO doping ratios,and the SnO2/rGO sensitive film was prepared by the coating method and the electrospinning method,respectively.Characterization analysis show that SnO2/rGO nanocomposites are prepared successfully and the SnO2 nanoparticles are dispersed on the rGO sheets.The surface of the sensitive film by electrospinning method is more uniform and the particle size formed is smaller.Besides,different rGO doping ratios also have an effect on the morphology.With the increase of doping ratio,SnO2 nanoparticles are gradually wrapped by rGO,forming a laminated structure.(2)The humidity characteristics of sensitive films prepared by the two method were tested respectively.Results show that 2wt%SnO2/rGO has better humidity performance in both methods.The sensitivity and response/recovery time of electrostatic spray SnO2/rGO film are 37491.2%and 80 s/4 s,which is better than that of coated SnO2/rGO film(1129.9%and 150 s/20 s).In addition,the electrostatic spray film has good repeatability and stability as well as greater practical value.Finally,the sensing mechanism was analyzed.The defect structure of SnO2 nanostructure and rGO could not only increase the specific surface area of the film,but also improve the electron transport efficiency,which promoted the sensing properties of the sensitive film.The electrostatic spray sensitive film has better uniformity and smaller particle size which is the key factor for its better performance.(3)The flexible humidity sensor based on electrospinning method was selected for practical application test.Temperature test results show that the sensors in the living environment(<40℃)were almost unaffected by temperature changes.Bending test results show that he sensitivity of the sensor increases with the decrease of the bending radius and bending number.Among them,the 2wt%SnO2/rGO sensor maintains stable humidity sensitivity after bending 1000 times,and its sensitivity and response recovery time have no significant changes.The results of human respiration test show that the flexible humidity sensor can not only accurately reflect the respiratory rate curves of different subjects,but also clearly reflect the different respiratory states of the same subjects before and after exercise,which shows the application potential in real-time respiration monitoring.