Study On Zinc Cobalt Oxide Materials And Its Gas Sensing Properties Toward Formaldehyde Gas

The continuous progress of human society benefits from the rapid development of science and technology,in the meantime environmental pollution has become an increasingly prominent problem.Among them,formaldehyde gas has wide range of sources and harmful aspects,and even can directly cause malignant tumors or cancer.Therefore,in order to avoid the harm of formaldehyde gas to human health,it is necessary to monitor formaldehyde gas in real time.And the monitoring method with excellent performance and economic benefits is conducive to wide application.Gas sensor method has the advantages of high sensitivity,small detection device and low cost,so it is an ideal method for monitoring toxic and harmful gases.In this paper,different morphologies of ZnCo₂O₄ and different ZnCo₂O₄ matrix composites were synthesized by microwave-assisted method,with their morphology,structure and gas sensing properties were studied,and the main results are as follows.（1）The samples of micron flower-like ZnCo₂O₄ assembled on nanosheets,Micron flowers/bouquets ZnCo₂O₄ and micron flower-like ZnCo₂O₄ assembled by nanowires have the highest response to formaldehyde gas.Among them,nanowires assembled with micron flower-like ZnCo₂O₄ samples have the best gas sensing performance to formaldehyde gas.In particular,the response of 4 h @ 120℃ ZnCo₂O₄ to 100 ppm formaldehyde gas is 9.24 at the optimal operating temperature of 120℃,and it has high selectivity.The response time and recovery time are 178 s and 196 s,respectively,and the detection limit is about 9 ppb.The gas sensing response behavior is mainly caused by the change of conductivity due to target gas adsorbed on the surface of the gas sensing material and reacted with chemisorbed oxygen,for a resistive gas sensor.（2）Ag loading can improve the gas sensing performance of ZnCo₂O₄ to formaldehyde gas.In particular,the response of 5 wt%Ag/ZnCo₂O₄ sample to 100 ppm formaldehyde gas is 15.36 at the optimal operating temperature of 120℃,which showed high selectivity.The response time is 160 s,the recovery time is 210 s,and the detection limit is about 2 ppb.The main reasons for the improvement of gas sensing performance of Ag/ZnCo₂O₄ samples include the improvement of conductivity of ZnCo₂O₄ by Ag loading and the catalysis of Ag monomer.（3）ZnO composite can improve the gas sensing performance of ZnCo₂O₄ toward formaldehyde gas.Especially,the response of 8 wt%ZnO/ZnCo₂O₄ sample to 100 ppm formaldehyde is 16.4 at the optimal operating temperature of 120℃,which has higher selectivity.The response time is 180 s,the recovery time is 240 s,and the detection limit is about 3 ppb.Since the close contact between ZnO and ZnCo₂O₄ and the formation of heterojunction,the gas sensing performance of ZnO/ZnCo₂O₄ samples can be improved by the heterojunction effect.The innovation of this paper is mainly reflected in the construction of ZnCo₂O₄ with special morphology to optimize its gas sensing performance to formaldehyde gas,and use of microwave-assisted method shortened the reaction time.Finally,the formaldehyde gas sensing material based on ZnCo₂O₄ with very low detection limit,low optimal operating temperature and high selectivity was obtained.