| Ethanol is a common volatile organic solvent,which can bring health problems and environmental problems to people when it is wildly used.Therefore,it is particularly important to detect and effectively monitor low-concentration ethanol.Various types of ethanol sensors are widely studied for use in many fields,such as disease diagnosis,drunk driving detection,environmental monitoring,and food industry.Among them,resistance-based gas sensors constructed by metal oxide semiconductors have the advantages of high sensitivity,short response time and low cost.Therefore,they are widely used in the detection of ethanol.Among numerous metal oxide sensing-materials,TiO2 exhibits excellent electrical properties,low cost and excellent stability,and shows wonderful sensing performance to ethanol,which is considered to be one of the most promising gas-sensing materials at present.Although researchers have made some progress in the research of TiO2 ethanol sensors,the sensing performance of these materials to ethanol still needs to be further improved.Studies have shown that the metal oxide nanostructures derived from metal-organic frameworks(MOF)have high specific surface area and high porosity.This structure is conducive to improve the gas-sensing performance of nanomaterials.Therefore,TiO2-based nanomaterials prepared based on MOF are expected to improve the sensing properties to ethanol.In addition,the construction of heterojunction can improve the resistance modulation ability of nanomaterials,so as to achieve the purpose of improving the gas-sensing performance.Based on the above background,in this thesis,MOF-based TiO2 porous nanosheets were prepared by solvothermal method.The ethanol gas-sensing properties of MOF-based TiO2 nanosheets and commercial TiO2 powder sensors were compared.The sensing mechanism of MOF-based TiO2 nanosheets was revealed.On this basis,MOF-based Co3O4-TiO2 heterojunction porous nanosheets were prepared by a two-step solvothermal method,and the mechanism of enhanced ethanol gas-sensing properties was studied.Specific research contents are as follows:Porous TiO2 nanosheets were further prepared by calcining the solvothermal prepared MOF precursor(MIL-125).The sensing results showed that the MOF-based TiO2 nanosheets exhibited lower optimum operating temperature and higher response.The response of MOF-based TiO2 nanosheets to 500 ppm ethanol at the optimum operating temperature(250?)was 46.12,which was 4.18 times that of the commercial TiO2 powder sensor at the optimum operating temperature(275?).In addition,MOF-based TiO2 nanosheet sensor also showed a lower detection limit,better ethanol selectivity and long-term stability.MOF-based TiO2 nanosheet sensor still showed a high response to ethanol in relatively high humidity environment.Studies showed that MOF-based TiO2 nanosheets have a special porous structure,which improved the adsorption and diffusion capacity of O2-and ethanol molecules,and enhanced the resistance modulation ability of the material.At the same time,the high-value state of adsorbed oxygen and the formation of rutile-anatase n-n junction were also the reasons for the enhanced sensing properties of TiO2 nanosheets.Porous Co3O4-TiO2 nanosheets with different molar ratios(8 mol%,12 mol%and 16 mol%)were prepared by calcination of MOF precursors(MIL-125 and ZIF-67)prepared via a two-step solvothermal method.Compared with pure TiO2 nanosheets,the porous Co3O4-TiO2 nanosheets had higher specific surface area and lower resistance.The gas sensing results showed that all Co3O4-TiO2 nanosheets sensors showed better ethanol sensing performance than pure TiO2 nanosheets sensor.Among all composite samples,12 mol%Co3O4-TiO2 nanosheets exhibited the highest response to ethanol.At the optimal operating temperature of 250?,the response of 12 mol%Co3O4-TiO2 sensor to 50 ppm ethanol(41.72)was 20.76 times that of pure TiO2 nanosheet sensor(2.01).In addition,the selectivity coefficient of 12 mol%Co3O4-TiO2 nanosheet sensor to ethanol(85.29%)is 3.06 times that of pure TiO2 nanosheet sensor(27.91%),exhibiting much better ethanol selectivity.The enhancement of ethanol sensing performance of Co3O4-TiO2 nanosheets was mainly attributed to the formation of p-n heterojunction,the increase of specific surface area and the enhancement of oxygen adsorption capacity. |
PDF Full Text Request