Study On Gas Sensing Properties Based On Metal Organic Framework And MXene

As people living standard gradually improve,the state environmental protection more and more attention,accordingly in the field of environmental protection,household,food,the safety of all kinds of poisonous and harmful gas detection are put forward higher requirements,especially the volatile and a pungent smell of hydrogen sulfide（H₂S）,formaldehyde（HCHO）and ammonia（NH₃）,and other gases.In recent years,metal-organic framework materials（MOF）have become the focus of gas sensor research because of their advantages of large specific surface area,adjustable pore size,diverse structure and surface modification,etc.Indium based organic framework materials CPP-3（In）is one of the representative.Existing studies have shown that In₂O₃prepared by roasting has good gas sensitivity to H₂S at low temperature.How to improve material sensitivity by doping and modifying MOF derived materials,including the formation of p-n,n-n heterojunction and other methods is a main research idea of this paper.In this paper,cobalt ion(Co²⁺)and cerium ion(Ce⁴⁺)were selected,respectively indium-based MOF material CPP-3（In）was doped,and then the p-n type Co₃O₄/In₂O₃and n-n type CeO₂/In₂O₃composites were prepared by high temperature roasting,and their gas sensitive properties were investigated in detail.In addition,as the research of room temperature gas sensor becomes a research trend,we also try to select new MXene material to reduce the working temperature and explore its gas sensitive performance.This paper mainly includes the following three parts:（1）A simple one-pot oil bath method was used to synthesize indium based MOF material containing cobalt ions Co²⁺/CPP-3（In）.The Co₃O₄/In₂O₃composite material was obtained by roasting it at 450℃for 1 h.The composition and morphology of samples before and after roasting were characterized by XRD,SEM and EDS.The Co₃O₄/In₂O₃composite material was uniformly coated on the ceramic tube and welded on the base for 7 days to test its gas sensitivity.The results show that the response value of the optimal ratio Co₃O₄/In₂O₃-2 sample to 5 ppm H₂S gas detection at 70℃is about 5 times that of pure In₂O₃,and it has good selectivity and repeatability.Finally,the mechanism of increasing gas sensitivity of Co₃O₄/In₂O₃composite gas sensor was explored from the structural characteristics of MOF material and the formation of p-n heterojunction.（2）A simple one-pot oil bath method was used to synthesize indium based MOF material Ce⁴⁺/CPP-3（In）containing cerium ions.The CeO₂/In₂O₃composite material was obtained after roasting at 450℃for 1 h.The composition,morphology and elemental state of the sample were characterized and analyzed by XRD,SEM and EDS.Finally,the sample was evenly coated on the ceramic tube for aging for 7 days to test the gas sensitive properties of CeO₂/In₂O₃composites.The results show that the response value of CeO₂/In₂O₃-3 sample to 50 ppm formaldehyde at the optimum temperature（160℃）is 59,about three times that of pure In₂O₃under the same conditions,and the detection limit is 1 ppm.The sensor also has excellent selectivity and repeatability.After that,the sensitivity mechanism of CeO₂/In₂O₃composite based gas sensor was explored from the structural characteristics of Indium-based MOF and the formation of n-n heterojunction.（3）Nano particles indium oxide（In₂O₃）were prepared by water bath method,and V₂CT_XMXene was etched by sodium fluoride（NaF）and hydrochloric acid（HCl）.Nano particles In₂O₃and V₂CT_XMXene were dissolved in deionized water and ultrasonic for 6hours,and finally dried by centrifugation.A series of V₂CT_X/In₂O₃gas sensing materials are obtained.The composition,morphology and element distribution of the sample were analyzed by XRD,SEM and EDS respectively.Finally,the sample was evenly coated on the ceramic tube and stood for 24 hours.Finally,the gas sensitivity of the sample was evaluated.The results showed that the optimum proportion of V₂CT_X/In₂O₃gas sensor at room temperature is38%for 50 ppm NH3(|R_g-R_a|/R_a（100%）of the response.In addition,the best ratio of V₂CT_X/In₂O₃gas sensor has excellent selectivity,good stability and repeatability.Finally,the mechanism of V₂CT_X/In₂O₃gas sensor sensitivity increase is explored from the structural characteristics of materials.