Research On Noble Metal Modified Bismuth Vanadate Gas-Sensing Materials And Sensing Mechanism

Wireless Sensor Networks,the technology support of the Internet of Things,have been widely used in military security,industrial control,environmental monitoring,smart home and other fields.Gas sensor is an important member of Wireless Sensor Networks,which can monitor and provide the information of gas composition and concentration in the environment,and is also the core basis of environmental Internet of things.Among all kinds of gas sensors,metal oxide semiconductor gas sensor has the advantages of high sensitivity,wide detection range,low cost and easy integration,and have been the research hotspot in the field of gas sensing.Researchers have been committed to develop metal oxide semiconductor gas-sensing materials and design sensitization strategies to obtain high performance gas sensor.Among various sensitization strategies of sensing materials,noble metal sensitizer modification method is the simplest and most effective,which can significantly change the carrier concentration/mobility,construct defect and heterojunction,and adjust the energy band of sensing materials.Whereas,the mechanism of noble metal sensitization needs to be further understood.On this basis,this dissertation selects the multi-element inorganic metal oxide bismuth vanadate（Bi VO₄）as the research object,which is modified by Pt and Ru O₂,respectively.The material structure and gas-sensing performance are tested and analyzed systematically,so that a better understanding of the general sensitization mechanism can be made.The main contents of this dissertation are as follows:1.A low content of Pt is modified onto the Bi VO₄ nanosheets by an in-situ reduction step of H₂Pt Cl₆,and the structure characterization and gas-sensing performance of Pt-modified Bi VO₄nanosheets and pristine Bi VO₄ are tested.The Pt-modified Bi VO₄ nanosheets show a good selectivity to acetone,with a response value of 12.5 to 100 ppm acetone,which is 3.2 times higher than that of Bi VO₄.The response time is as short as 2 s,and the theoretical detection limit is test to be 0.2 ppm.After storage of 60 days,the gas senser retains 98.9%of its initial response value.Based on the experimental data and the density functional calculation theory,the improvement on gas-sensing performance of Pt-Bi VO₄ is attributed to the synergism of electronic sensitization and chemical sensitization of Pt.2.A low content of Ru O₂ is modified onto the Bi VO₄ nanosheets by calcination,and both the pristine and Ru O₂ modified Bi VO₄ nanosheets are tested for structure characterization and gas-sensing performance.It is found that Ru O₂ modification can not only enhance the sensing response of the Bi VO₄ nanosheets,but also change the selectivity.The Ru O₂-modified Bi VO₄ nanosheets show much higher selectivity for xylene than acetone,the response value to 5 ppm xylene is increased by about 5 times（from 4.0 to 19.0）.The operating working temperature of Ru O₂-modified Bi VO₄ nanosheets decreases from 300℃to 260℃,and the theoretical detection limit is determined to be 15 ppb.The sensing device also shows a good long-term stability with only a 5%loss in response value.The gas sensing enhancement mechanism of Ru O₂-modified Bi VO₄nanosheets is attributed to the electronic sensitization from the p-n heterojunction formed at the interface between Ru O₂ and Bi VO₄,and the catalysis of RuO₂.