| The rapid development of science and technology updated chemical production equipment and production methods,raw materials used in the industrial process gas,solvent raw material and produce the types of gas are also numerous,most of these chemicals are flammable and explosive,or even poisonous and harmful.On the one hand,their leakage will cause serious environmental pollution problems such as greenhouse effect,ozone layer damage and air pollution.On the other hand,the explosion and fire caused by the leakage of these materials will endanger people's lives and national property security.In industrial production,if dangerous raw materials,intermediate products and products are not monitored in real time,they may also cause explosion,industrial poisoning and fire accidents.At the same time,as people living standard rise,liquefied petroleum gas,coal gas and natural gas as a family in the city of fuel is rapidly popularization,improper use or about these gases is caused by poor management are the dead injury news reports.Ethylene and carbon dioxide concentrations are also often controlled in the production and storage of agricultural products.The presence of CO2 could create a "greenhouse effect",namely the atmospheric CO2 gas can like a glass or plastic film in the greenhouse,absorb heat from the solar radiation,together,is not easy to disperse,leading to raise the temperature of the earths surface.The rise of the earth's temperature will bring a lot serious negative effects,such as polar ice dissolved rapidly,that makes the ocean surface increases,many coastal cities and some island was the first to suffer from the dangers of flood waters.The greenhouse effect will also lead to land desertification and reduced agricultural production.Therefore,the monitoring and control of CO2 gas is urgent.In addition,carbon dioxide gas sensors can be used in air quality monitoring,agricultural production,chemical materials,clean energy engineering and other fields.Acetone can easily change from a liquid to a gas in an air environment,volatilize into the atmosphere,and is a relatively toxic gas.So if acetone leaks into the air,there's a safety risk.Acetone does a lot of harm to human health.Normal human serum contains trace amounts of ketones because the body's fat produces ketones during metabolism.Due to a lack of insulin and insulin resistance hormone increase,people with diabetes can't normal use glucose,lipid metabolic disorder and existence,ketone body generated rapidly,oxidation is not complete,not in time to gather in the body,thus become ketonemia.Most of them adopt the traditional invasive method of lossy detection,i.e.,venous blood sampling.In recent years,the damage detection of diabetes and its complications diagnosis breakthrough tradition,non-invasive noninvasive NDT-breathing acetone in the gas into the line of sight of people,the study found,collection and analysis of patients with diabetes can breath gas to determine the patient's illness condition,acetone in diabetes patient breath gas content and healthy people out of acetone content,level of acetone in the healthy people out within the scope of 0.3 to 0.9 ppm,but usually acetone content in diabetes patients breathe out more than 1.8 ppm.Therefore,it is very promising to develop high sensitivity and selective acetone sensors suitable for the detection of low concentration acetone.Therefore,the effective detection and alarm of these toxic,dangerous and polluting gases are the necessary preconditions to solve the problem of environmental pollution and protect the safety of people's lives and property.Therefore,the research and development of gas sensor is not only in the past but also one of the international research hotspots and important fields for a long time to come.The research on gas sensor should take finding the right material as the starting point,which is also the most important work.The first broad-spectrum semiconductor gas-sensitive materials have been widely used in gas-sensitive sensors such as Sn02 and ZnO,but the understanding of their gas-sensitive mechanism is not very clear.The past researchers are keen to study metal oxide semiconductor gas sensitive material,and now researchers put much energy into the study of perovskite nanomaterials,ABO3 perovskite oxide has some unique advantages,first of all,the working stability of abnormal high;Secondly,it shows good selectivity and sensitivity to gas.Finally,the selectivity,sensitivity and working stability of gas-sensitive materials can be controlled by changing A and B elements or partially replacing A and B sites.The gas-sensitive properties of pure perovskite nanocrystals and doped perovskite nanocrystals are studied in this paper.Research work of this paper includes the following results:1.We studied the pure PrFeO3 in 120 ??300 ? temperature range of acetone gas sensitive and PrFeO3 doped with different proportion of graphene perovskite oxide gas sensitive characteristics of acetone.X-ray diffraction(XRD)results showed that we adopt the method of sol-gel preparation PrFeO3 powder orthogonal perovskite structure is single,obtained by the method of thermal diffusion doped graphene PrFeO3 powder material also has the same structure.The gas sensitive response of PrFeO3 nanocrystalline material gas sensor to acetone decreases with the increase of environmental humidity.In the best working temperature(200 ?),3 h under750? temperature annealing PrFeO3 nanocrystalline powders of gas sensors,and exposure to air dry relative humidity of 38%,48%and 62%when response to 1 ppm acetone gas respectively 1.95,1.57,1.45 and 1.37.When we increase the oxygen concentration in the atmosphere of the experimental environment,the gas sensitive response of PrFeO3 gas sensor to acetone will also increase.When working temperature is 200 ?,750 ? temperature annealing of 3 h PrFeO3 nanocrystalline powders exposed to oxygen concentration in the atmosphere gas sensor for the volume of 22%,33%and 44%when the response to 1 ppm acetone gas were 2.17,2.22 and 2.53.Our study found that doping a moderate amount of graphene can greatly improve the gas-sensitive response of gas sensors to acetone gas.Doped graphene ratio of 0 wt%,0.1 wt%,0.5 wt%,1 wt%,2 wt%and 3 wt%PrFeO3 gas sensor to 0.5 ppm acetone gas sensitive response of the gas were 1.51,1.78,2.08,2.49,2.15 and 1.44,the best working temperature is 200 ?,On the PrFeO3 gas sensor doped with 1 wt%graphene,we found that it has a high gas sensitivity response to 3ppm gas(acetone)to be measured,with a response value of 3.45.To 0.1 ppm,meanwhile,the trace of acetone,the gas sensor also showed particularly obvious response,the response value is 1.29.So we see the graphene doped PrFeO3 nanocrystalline materials used as a kind of acetone the potential value of the test material.2.We studied the pure PrFeO3,doped with different proportion of carbon nanotube(CNT)PrFeO3 perovskite nanocrystalline materials on gas-sensing properties of acetone gas sensor,control the temperature range 120 ? to 300?.X-ray diffraction(XRD)results showed that we adopt the method of sol-gel preparation PrFeO3 perovskite structure of powder material is single orthogonal,by thermal diffusion doping carbon nanotubes(CNT)PrFeO3 powder material also has the same structure.It was found in our study that the addition of appropriate carbon nanotubes(CNT)could significantly increase the gas sensitivity of gas sensors to acetone gas.In the best working temperature,the injection to the glass in the 0.5 ppm acetone gas conditions,carbon nanotubes(CNT)doping ratio of 0 wt%,0.1 wt%,0.5 wt%,1 wt%,2 wt%and 3 wt%PrFeO3 gas sensor for its gas sensitive response were 1.50,1.56,1.65,1.85,1.11 and 1.09.On the PrFeO3 gas sensor doped with carbon nanotubes(CNT),we found that it had very high gas-sensitive responses to 0.1 ppm and lppm acetone,with response values of 1.27 and 2.58 respectively.Therefore,we also see a bright future for carbon nanotube(CNT)doped PrFeO3 nanocrystalline materials to become a new type of acetone detection materials.3.We studied the blended with different proportion of Pd PrFeO3 and doped with different proportion of Ca PrFeO3 perovskite nanocrystalline materials gas-sensing properties of CO2 gas,we control the temperature range of 120 ??120 ?.We use sol-gel PrFeO3 precursor,and then calculate weighing different proportions of Pd and Ca,reoccupy thermal diffusion respectively the different proportion of Pd and Ca PrFeO3 nano material,get the final sample material,X ray diffraction(XRD)results showed that they are orthogonal perovskite structure.With just the right amount of Pd and the right amount of Ca both can improve PrFeO3 nanocrystalline powder material for CO2 gas sensitive response,when PrFeO3 nanocrystalline powder material adding 3 wt%of Pd,its gas sensitive to 2000 ppm CO2 response value is 1.40,the optimum working temperature 200 ?.When increase the relative humidity in the experimental environment,a record of 2000 ppm CO2 gas to the glass,under 200 ?,the pure PrFeO3 and doping of 3 wt%PdCl2 PrFeO3 declining gas sensitive response of the gas sensor.In other words,the presence of H2O molecule reduces the gas sensitivity of PrFeO3 and PrFeO3 gas sensors mixed with 3wt%PdCl2 to carbon dioxide gas.The best working temperature 200 ?,2000 ppm CO2 for gas concentration under test,Pr0.9 Ca0.1 FeO3 gas sensitive response of the gas sensor is 1.38.It can be seen that the addition of a certain amount of precious metal Pd and the partial replacement of Pr position with a certain amount of low price cation Ca can help improve the gas sensitivity performance of PrFeO3 gas sensor respectively.4.The experiment adopts the method of sol-gel preparation SmFeO3 nanocrystalline powder material,at 600 ?,respectively,700 ?,800 ? and 900 ?under the condition of annealing.Annealing temperature is 600 ? respectively,600 ?,800 ? and 900 ? SmFeO3 gas sensor response of 55000 ppmco2 gases were 2.69,3.07,1.73 and 1.60,this is in the best working temperature(240 ?)of gas sensitive performance.Through the contrast can be obtained:SmFeO3 nanocrystalline powder material gas sensor shows the best gas-sensing properties of the annealing temperature is 700 ?.The SmFeO3 precursor was doped with precious metal Pd with a proportion of 1wt%,3wt%,5wt%,7wt%and 9wt%.When working in the best temperature(200 ?)Pd doping amount of 0 wt%,1 wt%,3 wt%,5 wt%,7 wt and 9 wt%SmFeO3 nanocrystalline powder material of 4000 ppm CO2 response are respectively 1.43,1.63,1,76,1.62,1.57 and 1.49.Is obvious:when the Pd doped quality percentage is 3 wt%,SmFeO3 nano powder materials showed the best gas sensitive response,can also say that adding the right amount of Pd can be from a certain extent,improve SmFeO3 nano powder materials preparation and sensor of CO2 gas sensitive response.In addition,with the increase of air relative humidity in the experimental environment,the gas-sensitive response of SmFeO3 nanometer powder gas sensor with the doping amount of precious metal Pd of 3wt%to CO2 decreases. |
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