| The gas sensor is effective combination of gas detection and sensor,it can convert the concentration of target gases into electronic signal and output the result.The gas sensor possesses the advantage of easy integration and real-time detection,which make it plays a crucial part in the fields of environmental monitoring,guiding saft in industrial manufacturing and medical diagnosis.Currently,the most widely used metal oxide semiconductor gas sensor has caused extensive concern since its stable physical and chemical properties,high sensitivity and simple manufacturing.As the core piece of gas sensor,improving the utilization,recognition function and transformation function of gas sensor material will play significant role in gas sensing performance.Herein,the metal oxide（MOS）derived from metal-organic-framework（MOF）not only inherit the higher specific surface area of MOF,but also easier to form the hollow multi-shelled structure.Meanwhile,using bimetallic MOF as template,the metal oxide composite that containing heterojunction can be synthesized.This work was divided into the following parts:（1）Bimetal-organic frameworks of Ni-Co-BTC solid microspheres synthesized through hydrothermal method were acted as template to induce multishelled Ni O/Ni Co2O4 hollow microspheres by annealing treatment.When evaluated as gas sensing material,the optimal hybrid of Ni O/Ni Co2O4（the molar ration of Ni Co=1.5）multi-shelled hollow microspheres endowed a high sensitivity（17.86）to 100 ppm acetone with rapid response/recovery time（11/13s）under low working temperature（160℃）and the low detection limit reached 25 ppb.The enhanced mechanism was originated from the following aspects:the multishelled hollow architecture provided efficient diffusion path for gas molecules and sufficient active site for gas sensing reaction;the nanoscale p-p heterojunction created at Ni O and Ni Co2O4 nanoparticles interface amplified the resistance variation by tuning the potential barrier;the potent combination of the“chemical catalytic”effect of Ni O and the“electrical catalytic”effect of Ni Co2O4 improved the selective acetone detection.（2）By the method of coprecipitation,the Fe-Zn-PBA precursors were synthesized.After annealing treatment,multishelled Zn O/Zn Fe2O4 microspheres and multishelled Zn O/Zn Fe2O4octahedrons were obtained.The morphology evolution was originated from the increase of Fe/Zn molar ration of the Fe-Zn-PBA.After the gas sensing test,the multishelled Zn O/Zn Fe2O4octahedrons exhibited enhanced sensitivity（52.9）to 100 ppm ammonia with rapid response time（1s）under the working temperature of 190℃.The improved gas sensing performance can be explained as the following aspect:the unique multishelled octahedral structure possesses provided higher specific surface area which provided more active sites for gas sensing reaction;the higher percentage of Oc means the superior chemisorbed ability to oxygen species and ammonia,which is beneficial for sensing performance;the n-n heterojunction between Zn O and Zn Fe2O4 effectively modulated the electrical conductivity of sensing material,which improved the transformation function of gas sensor. |
