Synthesis Of Pure And Doped Cobalt Oxide Nanomaterials And Their Applications In Gas Sensing Properties

Co3O4 is a promising material to detect VOCs,due to its highly active surface elements states,which shows the relatively low working temperature and fast response and recovery time as gas sensor.In this paper,Co3O4 nanomaterials with four different morphologies were synthesized and their gas sensing properties were systematically studied for the aim of obtaining a high-performance VOCs gas sensor.Co3O4 nanowires were found to show excellent properties.In order to further improve the gas sensing properties of Co3O4 nanowires,the experimental conditions of hydrothermal temperature,the amount reactants and the calcination temperature were optimized,the influence of K doping on the gas sensing properties were also studied.A series of methods were used to analysis the difference,such as the morphology,the surface states and the crystal defects,to obtain a detailed explanation of the gas sensing mechanism.The main contents are summarized as follows:(1)Co3O4 with four kinds of morphologies were synthesized by using different cobalt salts:nanowires,nanosheets,nanoflowers and sea urchin-like Co3O4.The gas sensing properties of these four Co3O4 products were also studied,which showed that Co3O4 nanowires have the best sensing performance at the working temperature of 185?.The response of the sensor based on the nanowires reached 60 to 100 ppm ethanol,which was at least 4 times higher than the other Co3O4 products.The reason for the high performance of Co3O4 nanowires was due to its unique one-dimensional structure,abundant micro and mesoporous pores and the fast charge carrier mobility(2)The effects of the hydrothermal temperature,the ratio of the reactant and the calcining temperature of the precursor were systematic investigated on the morphology,the crystal structure and the gas sensitivity of Co3O4 nanowires.The relationship of calcination temperature with the structure and properties of nanowires were investigated through analyzing the microstructure and surface properties of Co3O4 nanowires.Based on the theory of hole accumulation layer,the gas sensing mechanism of Co3O4 nanowires was proposed.(3)The study of modification Co3O4 nano wires with K doping was carried out in our experiments.It was found that the gas sensitivity of the material was greatly improved by doping K,and the response was 305 to 100 ppm ethanol,which was more than twice of the pure Co3O4,and the working temperature was reduced from 185 to 165?.The doping of K has great influence on the crystal defects and surface oxygen of the Co3O4 nanowires,thus affects the gas sensing properties of the materials.