Research On High Performance Gas Sensor Based On One-dimensional Nanostructural Tin Dioxide

With the rapid development of our economy and society,the pollution of atmospheric and micro environment has become one of the most concerned topics.Accurate and real-time detection of toxic,harmful,flammable and explosive gases in the environment is of great significance to environmental governance,human health and life safety.As a device or system for detecting gas types and concentrations,gas sensors are widely used in the fields of atmospheric and micro environment monitoring,industrial and home safety monitoring,medical and health diagnosis due to their advantages of small size,low cost,easy fabrication,integration and online measurement.Among the gas sensors based on various principles,oxide semiconductor gas sensors have the advantages of all-solid state,high sensitivity and high reliability.How to improve the sensitivity,selectivity and stability of oxide semiconductor gas sensors is the core scientific problem in this field and the key to its application.As for oxide semiconductor gas sensors,their performance is closely related to the structure and composition of sensing materials.With the development of nano science and micro-nano processing technology,people found oxide semiconductor materials has unique mechanical,optical,electrical,and catalytic properties in the nanoscale.In addition,specific surface area of the oxide semiconductor nanomaterials will increase with the decrease of the grain size,and the movement of the carriers is also affected by the grain size.In order to further improve the performance of oxide semiconductor gas sensors and meet the needs of practical applications,the design and fabrication of high-performance oxide semiconductor nanomaterials has become the core part of the research.With the development of electrospinning technology,it has been found that one-dimensional oxide semiconductor nanomaterials are very suitable for gas sensing materials due to their large length-diameter ratio and special porous nanoparticles accumulation structure.Therefore,in this paper,one-dimensional tin dioxide nanofibers were used as the matrix sensing materials,and the receptor function,transducer function and utility factor of the sensing materials were optimized through the modification technology of heterogeneous cation in situ doping,so as to improve the performance of the gas sensors.Specific research contents are as follows:1.Pure and 1,3,5 mol%Co doped SnO₂ nanofibers were prepared by electrospinning method.SEM and TEM images showed that the synthesized samples were uniform nanofibrous structures with diameters of about 100 nm.Through analyzing the XRD characterization results,it was found that with the increase of doping amount,the width of the diffraction peaks widened and the diffraction peaks were shifted to higher angle,indicating that the grain size of the nanofibers was gradually reduced and the Co ion was successfully incorporated into the lattice of SnO₂,and the growth of SnO₂ grain was effectively inhibited.The obtained sensing materials were imprinted on the planar electrode substrate by hot pressing technology.The results showed that compared with the pure SnO₂ nanofibers,the SnO₂ nanofibers doped with 3 mol%Co showed good selectivity to ethanol gas and the highest improvement of response.At the optimum operating temperature of 300?,the response value of 100 ppm ethanol gas was 40.1,which was 4 times higher than that of pure SnO₂ nanofibers.At the same time,the gas sensors showed good repeatability and stability.The small size effect of the structure unit,the regulation of the carrier concentration of SnO₂ nanofibers by Co ion doping and the formation of p-n heterostructure between Co₃O₄ and SnO₂ were the main reasons for the improvement of gas sensing characteristics.2.RhCl₃ was used as the starting source,and Rh³⁺in-situ doped SnO₂ nanofibers were prepared by electrospinning and subsequent annealing process.The influence of doping amount on gas sensing characteristics was studied and the optimal doping amount was determined.Various characterization results of morphology,structure and composition showed that the Rh-SnO₂ nanomaterials had a nanofibrous structure with a diameter of about 150 nm,which was composed of nanoparticles.The grain size decreased from the 9.9 nm?pure SnO₂?to 4.4 nm?1 mol%Ru-SnO₂?with the increase of doping amount.The synthesized samples were uniformly coated on the surface of the planar electrode substrate and made into a planar sensor.The gas sensing test results showed that Rh³⁺doping could significantly improved the selectivity and sensitivity of SnO₂ to acetone gas.Among all samples,0.5 mol%Rh-SnO₂ nanofibers had the largest increase in sensitivity to acetone gas.At the optimal operating temperature of 200?,its response value to 50 ppm acetone gas was 60.6,which was 9.6 times higher than that of undoped SnO₂ nanofibers.However,the response values of other test gases were not improved as much as that of acetone,indicating that the sensor has a good selectivity to acetone.Meanwhile,the sensor also showed a low detection limit?1 ppm?,fast response and recovery characteristics?response time is 2 s,recovery time is 64 s?and good repeatability.The sensitization mechanism of Rh ion doping was explained as follows:the decrease of grain size of SnO₂ caused by Rh ion doping,the change of carrier concentration and the electron sensitization effect of Rh₂O₃ were the main reasons for improving gas sensitivity.In addition,according to the characterization results of XPS,the increase of chemisorbed oxygen concentration and vacancy oxygen concentration caused by the addition of Rh ion also played an important role in the improvement of sensing characteristics.3.Ru ion was selected as the dopant,and Ru⁴⁺in-situ doped SnO₂ nanofibers were synthesized by electrospinning technology and annealing treatment.The results of SEM and TEM characterizations showed that the diameter of the nanofibers were mainly distributed in the range of 120 nm-150 nm and had a porous surface.The XRD pattern showed that the diffraction peaks of SnO₂ had obvious high-angle migration and broadening with the incorporation of Ru ion,which indicated that the lattice of Ru⁴⁺incorporation reduced the grain size.The undoped and 1,2,3 mol%Ru-SnO₂nanofibers were coated on the planar electrode substrate to produce the gas sensors and the gas sensitivity of the sensors was systematically tested.Compared with pure SnO₂ nanofibers,the sensitivity and selectivity of Ru doped nanofibers to acetone gas were significantly improved,especially 2 mol%Ru-SnO₂ nanofibers.At the optimum operating temperature of 200?,its response value to 100 ppm acetone gas was 118.8,which was 12 times higher than that of pure SnO₂ nanofibers.It was noteworthy that the gas sensors have a fast response?response time of 1 s?and the detection threshold was reduced to the order of ppb?500 ppb?,indicating its potential application in the detection of diabetes expiratory markers.The main reasons for the significant increase in acetone gas sensitivity were that Ru ion incorporation regulated the size of structural units and the concentration of chemisorbed oxygen and vacancy oxygen on the surface.The decrease in grain size led to the increase in the proportion of electron depletion layer,and the increase of vacancy oxygen concentration would provide more active sites for gas sensing reactions,promoting the adsorption of gases on the surface of the sensing materials,while the increase of chemisorbed oxygen made more electrons participate in the transfer.