Study On The Preparation And Gas Sensing Performance Of Zinc-Based VOC Sensitive Materials

Volatile organic compound（VOC）is a one kind of air pollutes and its highly efficient detection is great important for public safety and life’s healthy protection.As an advanced gas-detection technique,gas sensor based on metal oxide semiconductor（MOS）has stimulated much interest owing to its merits of low cost,simple manipulation,easy integration,and so on.To upgrade the sensitivity,selectivity and response-recovery speed of MOS sensor and meet the needs of some newly appeared fields,such as intelligent housing system and exhalation detection,designed synthesis of MOS nanomaterials with high gas sensing performance has been one of hotspots currently.In this thesis,with the expect of improving the VOC sensing performance of ZnO and Zn₂SnO₄,some zinc-based gas sensing materials were prepared based on our thought of combining the sensitization effect of porous structure with that of element doping,noble metals surface modification and heterojunction,respectively.The influence of material’s composition and microstructure on the VOC sensing performance were investigated,and their gas sensing mechanism was discussed.（1）By using the hydrothermally prepared Zn₅（CO₃）₂（OH）₆as sacrificial template,flower-like ZnO hierarchical structures assembled with single-crystalline porous nanoplates of 30～40 nm in thickness were prepared.At the optimal working temperature of 270℃,the ZnO sensor showed good selectivity to TEA.Its response to100 ppm TEA was as high as 360 and its LOD was as low as 5 ppb.The unique hierarchical structure should be responsible for its superior TEA sensing performance.（2）Bi-doped ZnO porous nanoplates were prepared via an“immersion-freeze drying-calcination”method by using the self-made Zn₅（CO₃）₂（OH）₆as precursor.In our Bi-doped ZnO,Bi replaced Znin ZnO lattice as the form of Bi³⁺.After doping with Bi,the ZnO sensor showed obvious enhancements in TEA sensing performance,such as lower optimal working temperature（230℃vs 270℃）and much higher sensitivity（130.95/ppm vs 16.16/ppm for 1-100 ppm TEA）.Such results indicate that doping with Bi is an effective method to improve the gas sensing performance of ZnO.（3）Porous ZnO polyhedrons assembled with 40～70 nm nanoparticles were prepared by using self-made zinc oxalate as sacrificial template.ZnS nanoparticles about 5～10 nm in size were modified on the ZnO porous polyhedrons via a hydrothermal sulfurization process.After introduction of ZnS-ZnO heterojunctions,the ZnO porous polyhedrons showed apparent improvements in TEA sensing performance,such as higher sensitivity（14 vs 7.6 for 50 ppm TEA）,faster response-recovery speed（5/119 s vs 7/147 s for 50 ppm TEA）and better selectivity.These improvements should be mainly attributed to the sensitization effects of ZnS-ZnO heterojunctions.（4）Nest-like ZnO hierarchical structure was prepared via a solvothermal method,on which Au nanoparticles was decorated by an immersion-calcination method.After decoration with Au nanoparticles,the ZnO sensor showed a decrease of 30^oC in its working temperature for sensing TEA,and its sensitivity to 1-500 ppm TEA was increased from 0.49 to 3.10/ppm.In addition,the Au-decoration also endows the nest-like ZnO sensor a faster response speed,whose response-recovery time decrease from 9/35 to 4/26s.These improvements should be attributed to the electron sensitization and chemical sensitization effects of Au on nest-like ZnO.（5）Zn₂SnO₄/RGO nanocomposite was prepared via a reliable solvothermal-calcination method by using self-made oxide graphene（GO）as precursor.The prepared Zn₂SnO₄/RGO composite features the in-situ modification of～20 nm Zn₂SnO₄nanoparticles on RGO with good dispersion.The obtained Zn₂SnO₄/RGO composite showed an enhanced ethanol sensing performance.Its response to 100 ppm ethanol increased from 6 to 38,and its response-recovery speed for 5-1200 ppm was also increased.These improvements were attributed to the good conductivity of RGO and the sensitization of RGO-Zn₂SnO₄heterojunction.（6）Porous and hollow porous Zn₂SnO₄/SnO₂microspheres were prepared by directly calcinating and etching-calcinating the hydrothermally prepared ZnSn（OH）₆microspheres,respectively.After the structural evolution from porous microsphere to porous hollow microsphere,the sensitivity and response-recovery speed of Zn₂SnO₄/SnO₂for sensing TEA was increased,indicating that the porous hollow microsphere structure is more favorable for gas sensing performance of MOS.This thesis includes 90 figures,16 tables and 195 references.