Preparation Of ZnO And Bi₂MoO₆-Based Composites And Their Gas-Sensitive Properties

The rapid development of industry and the improvement of human quality of life will bring a series of environmental pollution problems,natural and industrial NO₂and H₂S gases are also very harmful to humans.NO₂mainly comes from some common high temperature combustion process in life,inhalation of NO₂will cause damage to the human respiratory tract,when exposed to an average concentration of 82 ppb NO₂for more than one hour will be directly endangered life safety.H₂S is a colorless but strong-smelling toxic gas,which is closely related to human life,and low concentrations of H₂S can induce a series of neurological and Respiratory system diseases.The gas sensor relies on its many advantages and has been explored and discovered by many researchers and used to monitor some toxic and harmful gases in real time to protect our health.This paper focuses on two n-type oxide semiconductor materials,binary metal oxide zinc oxide（ZnO）and ternary metal oxide bismuth molybdate（Bi₂MoO₆）.We have successfully synthesized NO₂and H₂S gas sensors with excellent sensing performance by doping precious metals and building heterostructures to enhance the sensitivity of the native materials to the target gases.The specific research work is as follows:（1）The first work in this paper is based on the synthesis of noble metal Rh-doped ZnO nanofibers by electrostatic spinning method.The successful synthesis of Rh-doped ZnO nanofibers was confirmed by XRD,SEM and XPS in terms of crystal structure as well as surface morphology,and the detectable lower limit of the sensor is 50 ppb of NO₂,which is sufficient for the daily needs of human beings.By comparing the different molar ratios of Rh doped into the lattice of ZnO,it was founded that the sensor achieved the best sensing performance for NO₂at the optimum operating temperature of 150℃with the response of36.17 and 1.04 for 10 ppm and 50 ppb NO₂,respectively,and the sensor has good gas selectivity,repeatability and long-term stability.The improved gas-sensitive performance after Rh doping is attributed to the abundant oxygen vacancy defects on the material surface and the catalytic activity of Rh for H₂O and NO₂.（2）The second work,namely,the synthesis of Bi₂MoO₆-CuO heterostructure films by sol-gel method,XRD results showed that both Bi₂MoO₆and CuO were present in the samples,and TEM obviously found the formation of Bi₂MoO₆and CuO heterostructures.The results of gas-sensitive tests showed that the Bi₂MoO₆-CuO composite had the highest sensitivity to H₂S at the optimum operating temperature of 70°C and the lower detection limit was up to 100 ppb.The response of the sensor to H₂S at 1 ppm and 100 ppb is 7.96 and 1.12 respectively.In addition,a series of concentration gradient tests,repeatability tests and gas selectivity tests have demonstrated the good sensing performance of the sensor for H₂S gas,the improved gas-sensitive performance is attributed to the successful construction of Bi₂MoO₆-CuO heterostructures.