Preparation And Gas Sensing Properties Of In₂O₃ Derived From The Template Of Indium-organic Framework

Metal oxide gas sensors attract more attentions due to their advantages such as short response time,low cost,controllable preparation,simple integration and good suitability for the design of portable instruments.However,some deficiencies of traditional metal oxide have impeded the improvement in gas sensing,such as high operating temperature,high energy consumption,long response/recovery time,short shelf-life and so on.In recent years,metal-organic frameworks(MOFs),as a novel class of porous inorganic-organic hybrid materials,have received a great deal of attention due to their fascinating features,such as large specific surface area,tunable pore structures and excellent performance.Metal oxide derived from MOF can form a porous and hollow structure while retaining the original framework,which is attributed to gas absorption and electron transfer.Therefore,MOF can become a multifunctional precursor or template to construct metal oxide with porous micro/nano structure,this provide a new research idea for gas sensing field.Herein,a simple oil bath heating method was used to prepare the In-MOF materials CPP-3(In).The metal ions were impregnated into the porous structure of CPP-3(In)by impregnation.Then as the template,derivative materials were obtained through a simple calcination process.The sensors using above metal oxide composite as sensing materials show the effective detection of H₂S at low temperature,and the sensing mechanism was thoroughly discussed in the paper.The main contents are as follows:(1)In-MOF materials CPP-3(In)were prepared by a simple oil bath heating method.The composition and structure of the sample were analyzed by XRD and SEM.CPP-3(In)powders revealed hexagonal rods with a smooth surface.Most of the rods were homogeneous in size with an average diameter of 2.0?m and length of 10.0?m.After being calcined in the air,CPP-3(In)were completely converted into In₂O₃.Then the above samples were prepared into gas sensor,and the gas responses of 10ppm H₂S at different temperatures was tested.The results showed that the In₂O₃based sensor could reduce the optimized working temperature to 70°C with 26.9 of response.Furthermore,the gas sensor exhibited excellent selectivity and repeatability.(2)In-MOF materials CPP-3(In)were prepared by a simple oil bath heating method.The silver cation were impregnated into the porous structure of CPP-3(In)by impregnation.Then as the template,Ag/In₂O₃were obtained through calcining Ag⁺/CPP-3(In).The composition,structure and morphology of the sample were analyzed by XRD,SEM,TEM,XPS and EDX.The gas sensitivity test results showed that the Ag/In₂O₃(2.5 wt%)based sensor exhibited the highest response of 119 to 5ppm H₂S at 70°C,which is 4 times higher than that of pristine In₂O₃.In addition,the gas sensor based on Ag/In₂O₃(2.5 wt%)has the advantages of short response time,low detection limit,low operating temperature,and excellent selectivity to other interfering gases.Ag play a role as a catalyst to enhance the gas sensitivity.(3)In-MOF materials CPP-3(In)were prepared by a simple oil bath heating method.The copper cation were impregnated into the porous structure of CPP-3(In).After being calcined in the air,Cu²⁺/CPP-3(In)were completely converted into Cu O/In₂O₃.The composition,element state and morphology of the sample were analyzed by XRD,SEM,TEM,EDX,XPS and BET.The gas sensitivity test results showed that the Cu O/In₂O₃(3.5 wt%)based sensor exhibited the highest response of229.3 to 5 ppm H₂S at 70°C,which is 8.5 times higher than that of pristine In₂O₃,the detection limit was reduced to 200 ppb,the response time was reduced to within10 seconds,selectivity,stability and repeatability was excellent.At the same time,the mechanism of enhancing the gas sensitivity of the bamboo-like Cu O/In₂O₃gas sensor was discussed from the aspects of:1)the species and amount of chemisorbed oxygen on the surface;2)chemical reaction between Cu O and H₂S on the surface of grain;3)the unique mesoporous structure and rough surface of Cu O/In₂O₃heterostructure;4)the formation of p-n heterojunction.