Synthesis,Morphology Controllable Of Au Nanoparticles Modified Metal Oxide Nanostructures And Their Gas Sensing Properties

Recently,people living qualities have greatly improved with the rapid growth of industrialization and social economy,accompanied serious environmental pollution problems.Especially the emission of hazardous gases may cause severe threat to our health and property safety.Therefore,great efforts have been focused on development high performance efficient methods for detection of toxic and harmful gases.Gas sensor has been widely used gas detection field because of the advantages of simple preparation,low cost,small size and so on.Additionally,the sensing properties of gas sensors are significant affected by the sensing material,so the development of sensing materials with high properties are important aspect for gas sensors.At present,metal oxide semiconductor（MOS）gas sensors have been widely used for hazardous gases detection because of their high sensitivity and good stability.While,MOS-based gas sensors still face many problems including poor selectivity,slow response and recovery speed due to the limitation of the inherent properties.Meanwhile,MetalOrganic Frameworks（MOFs）have become one of the most popular materials due to the properties of large specific surface area,high porosity,adjustable pore size and structural diversity.However,most of MOFs present the shortcomings of poor electrical conductivity and few redox active,which block their application as gas sensitive materials.The previous experiments demonstrated that MOFs derivatives not only keep the advantages of MOFs material but also greatly improve the electrical conductivity,stability and gas sensing properties,which have been widely used as gas sensitive material.What’s more,considering the limitations of sensitivity and limit of detection,the different methods have been adopted for improvement the gas sensing properties including morphological control,heterojunction construction and noble metals（Au,Pd,Pt,etc.）modification.Therefore,it is promising to develop the noble metals modified MOFs-based gas sensors for practical application.The detail results in this paper are as follows:（1）In order to study the effect of Au content on the performance ofα-Fe₂O₃ sensor,the different concentrations（0,0.25 mol%,0.5 mol%,1 mol%）of Au NPs modifiedα-Fe₂O₃nanodisk structure-based gas sensors were prepared by hydrothermal method.The obtained gas sensitivity test results demonstrated that 0.5 mol%Au NPs modifiedα-Fe₂O₃sensor exhibits the best gas sensing properties,and the measured response could reach to 19.5 toward 100 ppm acetone at the optimum working temperature of 275℃.Meanwhile,the gas sensor also showed the fastest response and recovery time.（2）The dodecahedral ZIF-8/ZIF-67 precursor template was prepared by solvothermal method,and the（0,1 mol%,2 mol%,3 mol%,4 mol%）Au@ZnO/Co₃O₄ hollow dodecahedron composite structures were synthesized by subsequent controlled pyrolysis.The results of gas sensing properties detection showed that the response of ZnO/Co₃O₄ hollow dodecahedron gas sensor can reach to 17.8 toward 50 ppm n-butanol under the optimum working temperature of240℃.At the same time,the introduce of Au NPs could significantly improve the gas sensing properties and reduced the optimum working temperature to 200℃.Particularly the 2 mol%Au@ZnO/Co₃O₄ gas sensor exhibited the highest response（95.5）to 50 ppm n-butanol,the fastest response/recovery time（11 s/16 s）and the lowest limit of detection（1 ppb）.（3）In order to study the influence of different morphologies on the gas sensitivity of sensitive materials,the ZnO/Co₃O₄ polyhedrons were synthesized with（0,0.25 mol%,0.5 mol%and 1 mol%）of Au NPs by adjusting the proportion of metal ions（Zn,Co）and organic ligand.The gas sensing experiments displayed that the measured response of ZnO/Co₃O₄ polyhedrons sensor was 102.9 toward 100 ppm triethylamine gas under the optimum working temperature（260℃）,which was much higher than other tested gases.And the 0.5 mol%Au NPs modified cubic ZnO/Co₃O₄sensor exhibited the best sensing performance:the measured response could reach to 628.84 to 100 ppm triethylamine at 240℃,the response/recovery time was as soon as2 s/7 s,showed good selectivity and repeatability.（4）The surface charge model was used to analyze the gas sensing mechanism Au@α-Fe2O3of nanodisks and Au@ZnO/Co₃O₄ composites gas sensors.The oxygen molecules in the air will become the adsorbed oxygen ions on the surface of the sensitive materials by capturing free electrons,then the chemical reaction will be produced between adsorbed oxygen ions and tested gas molecules.The responses can be obtained by measuring the resistance change of gas sensors.For ZnO/Co₃O₄sensor,the formation of p-n heterojunctions at the interface of ZnO and Co₃O₄ intensifies the electron flow in the sensitive material and increases the initial resistance of the sensor.In addition,the synergism of electronic sensitization and chemical sensitization of Au NPs improves the gas sensitivity of the sensor.