The Preparation Of Copper Oxide/Tungsten Oxide Nanomaterials And Its Application In Gas Sensors

With the rapid development of social economy and the continuous improvement of industrialization and urbanization,the problem of air pollution is becoming more and more serious.The efficient gas sensors attach more and more peoples’s interesting.Hydrogen sulfide（H₂S）and ammonia（NH₃）are both malodorous gases and could cause damage to human organs at low concentrations.Therefore,effective detection of trace amounts of H₂S and NH₃ gases in the environment is significant for humanbeing’s healthy.Metal oxide gas sensors have been widely used due to the low cost,stable operation and portability.However,high energy consumption,poor stability and short life limit their practical applications.In order to solve the above problems,in this paper,we use p-type semiconductor CuO and n-type semiconductor WO₃ as the main sensitive materials to prepare effective gas-sensors.The detection of H₂S gas at low temperature/room temperature was achieved by doping and recombination.The metal oxide was successfully combined with the flexible substrates and NH₃ gas could be detected at room temperature.The gas sensing mechanism was also studied in detail.The main research contents of this paper are as follows:（1）Pure CuO and Au,Ag and Cr doped CuO micro-nanostructures were prepared by a simple water bath heating method.The composition and structure of the sample were analyzed by XRD,SEM and ICP.Then the above samples were prepared into gas sensor,and the gas sensitivity of 10 ppm H₂S at different temperatures was tested.The results show that the CuO sensor dopped with 1.25 wt%Au exhibited the best sensing properties for H₂S,and the response value reached 128 at the optimum operating temperature（40 ^oC）,which is 25.8times higher than that of the pure CuO gas sensor（4.96）.At the same time,the detection limit of Au droped CuO gas sensor is 100 ppb,and it has good selectivity and stability.（2）Flower-like WO₃ microspheres and flower-like WO₃/CuO microspheres were prepared by a simple hydrothermal method.The morphology,structure and composition of the samples were characterized by XRD,SEM,TEM and BET.The above samples were prepared into gas sensors and exposed to H₂S,NO₂,NH₃,NO,CO,toluene,xylene,benzene,methanol,ethanol and acetone for measuring sensing properties.The results show that the gas sensor based on the flower-like WO₃ microsphere has the best gas sensitivity to 5 ppm H₂S at an operating temperature of 80°C,and the detection limit is 500 ppb.Gas sensor based on flower-like WO₃/CuO microspheres with n（WO₃）:n（CuO）=7:1,the response value of 5 ppm H₂S gas at the optimal working temperature（80 ^oC）reached 105,the detection limit was reduced to 300ppb,the selectivity was enhanced,stability and repeatability was excellent and response time was fast.We also discussed the mechanism of the flower-like WO₃/CuO microsphere gas sensor from the aspects of the formation of p-n heterostructure.（3）Flower-like WO₃ microspheres were prepared by a simple hydrothermal method,and then mixed with aniline to prepare PANI/WO₃ composite material and PANI/WO₃ thread by in-situ polymerization.The morphology,structure and composition of the samples were characterized by XRD,SEM and EDX.The above thread is clamped on both ends of the self-made fixture for gas sensitivity test.The results show that the PANI/WO₃ thread has a response value of 7 to 100 ppm NH₃ gas at room temperature,which is more than twice that of pure PANI thread（2.6）.The response（¹65 s）and recovery（³40 s）of the PANI/WO₃cotton are fast,and it has good selectivity,repeatability and stability.Moreover,we discuss the formation of p-n heterojunction and the improvement of gas sensitivity of fiber structure.