Study On Properties Of Noble Metals Decorating On Gas Sensitive Materials Based On In2O₃/SnO₂

Semiconductor metal oxide gas sensing materials are widely used in many fields,such as environmental monitoring,safety alarm,indoor environment and disease diagnosis due to their advantages of simple fabrication,low cost,high response and good stability.The n-type semiconductor metal oxide represented by In₂O₃ and SnO₂ is widely used in gas sensors,photo-catalysis and transformation and magnetics which due to its characteristics of wide band gap,good electric conductivity,strong thermal stability,easy construction of a micro-Catalytic and transformation and magnetism and other applications.In recent years,research results continue to emerge,there are limitations behind the developments:single semiconductor gas sensor in the detection process are less stable,less sensitive,poor selectivity and more difficult to detect the high stability gas molecules.Modification is an effective method to improve the sensitivity,stability and selectivity of the gas sensor.Precious metals has excellent catalytic activity which can greatly accelerate the transition of electrons from the surface layer of sensing materials,and thereby achieving the purpose of improving gas sensing performances.In this thesis,the noble metal modificated of In₂O₃ and SnO₂ semiconductor materials with specific morphology by simple impregnation method were achieved,and the related gas sensitivity properties were systematically studied,resulting in the real-time monitoring of toxic and harmful gases.This thesis contains the following three results:?1?Pt and PtO₂ nanoparticles were successfully modified on nanosheet-assembled In₂O₃ hollow microspheres using a simple impregnation method.The composites showed good sensing properties for ppb formaldehyde.The Pt-doped In₂O₃ composite has a high response?R=172,50 ppm?,low detection limit?60 ppb?,short response-recovery time?1 s,51 s?and excellent cycle stability?30 times?toward formaldehyde at a low operating temperatures?120°C?,and the response value is 3 times of the pure In₂O₃.The enhanced gas sensing properties are mainly due to the Schottky barrier and the catalysis of Pt nanoparticles.?2?The synergetic effect of bimetallic is attracting so much attention.Here,we successfully modificated double noble metal Pt-Au nanocatalyst on In₂O₃ ultrathin nanosheets.The sample Pt_0.3Au_0.7-In₂O₃ composites showed high gas sensitivity to acetone even with ppb level at 160°C and 95%RH.Compared with the pure In₂O₃ and reported literatures of acetone sensors,the composite has the characteristics of low working temperature,high sensitivity,good selectivity and stability.In addition,even at high humidity atmosphere?up to 95%RH?,its response to 1.8 ppm acetone?minimum acetone concentration in exhaled breath of diabetic?is about 44%higher than that of 0.9ppm?maximum acetone concentration in exhaled breath of normal people?,which can be clearly distinguished for the diagnosis of diabetes in more non-invasive and accurate way.The excellent sensing performance indicates that bimetallic Pt–Au decoration is an effect way,improving the acetone sensing ability of In₂O₃.?3?The noble metal Pd is considered as good catalytic activity in gas sensing research,which can effectively reduce the working temperature and increase the gas sensing response.A simple impregnation method was used to modify Pd on the surface of SnO₂ microspheres.Pd-SnO₂ nanospheres composites were successfully prepared for the detection of CO gas at low temperature.In the meanwhile,by adjusting the amount of palladium chloride,sample 4 mol%Pd-SnO₂ was found to exhibit excellent gas sensitivity of 31 to 200 ppm CO with short response time?30 s?at a low temperature of35°C and low detection limit?5 ppm?.Most importantly,it shows good selectivity with little sensitivity to hydrogen and methane gases under the same conditions.