Design Of ZnFe₂O₄?NiO Nanostructures And Their Gas Sensing Properties

With the rapid development of the world industrialization level,there are irritation,harmful and toxic gas emissions and leakage is also increasing,seriously endangering the health of people.Therefore,the production and manufacture of high performance real-time monitoring gas sensors to monitor the surrounding gas environment is becoming more and more urgent.In general,gas sensor is the component that outputs the corresponding electrical signal with the change of gas type and concentration,and it is the sensitive material that determines the performance of gas sensor.Nanomaterials with microstructures are widely used in energy storage,catalysis and integrated circuits due to their unique properties.Among them,metal oxide semiconductor nanomaterials have been widely used in gas sensors because of their stable chemical properties,cheap and easy to obtain,and have shown satisfactory performance.However,with the increasing demand,gas sensors have good performance in sensitivity,response/recovery time and selectivity.How to improve the comprehensive properties of nanomaterials by controlling the microstructure and composition of nanomaterials is the direction of our research.The main contents of this thesis are as follows:1.Preparation of porous ZnFe2O4 nanorods with reticular pore structure by in-situ decomposition of ZnFe2(C2O4)3 as precursor and their gas-sensing propertiesFor the n-type semiconductor material ZnFe2O4,in order to keep the size of small nanoparticles and good pore structure at the same time,the sensitivity of the sensor is improved,and the fast response/recovery rate is obtained.Porous ZnFe2O4 nanorods were prepared by non-surfactant assisted hydrothermal method and in situ calcination conversion.The gas-sensing properties of the nanorods were tested.The results show that the sensitivity of porous ZnFe2O4 nanorod gas sensor to 100 ppm acetone is 52.8,and its response/recovery time is shortened to 1/11 s.It is concluded that well-dispersed pores and small interlinked nanoparticles can not only provide a through gas transport channel,but also guarantee a larger specific surface area and corresponding active sites.This makes the gas sensor have faster response/recovery rate and higher sensitivity.2.Hollow graded NiO nanorods fabricated by conversion of NiC2O4 as precursor to ultrathin Nanochips and their Iron-doped Gas-Sensitive PropertiesFirst,based on the work of others,we further synthesized NiC2O4 nanorods by a simple hydrothermal method.Porous NiC2O4 nanorods with reticular pore structure were prepared by in situ calcination of NiO nanorods.Then,by the precursor conversion method of Kokendal effect,the simple NiC2O4 nanorods with uniform one-dimensional structure reacted with naoh solution to form hollow graded NiO nanorods assembled from ultrathin nanowires.In addition,the product obtained by the method keeps the geometric shape of the NiC2O4 nanorod precursor perfectly,and the resulting nano-pore structure not only forms a porous hollow-out structure,It also makes the conversion of the nickel oxalate precursor in the inner layer more thorough.The hollow graded NiO nanorods formed by the evolution of ultrathin nanocrystals have the characteristics of open hollow tubular structure and special "nanofilm-sodium rice bar" composite structure.We tested the gas sensor properties of nio nanocrystals without nanostructures,porous nio nanorods and nio nanorods assembled from ultrathin nanorods,as the nanostructures changed.The response/recovery time to 100 ppm ethanol was shorter and shorter:3.1/15,1 s?1.8/10.5 s and 0.4/1.5 s,respectively.But their sensitivities were low,4.72?4.58 and 5.58,respectively.In order to improve the comprehensive properties of the NiO nanorods,we doped the nanocrystalline nio nanorods with small amounts of iron.It was found that the doping sensitivity of 3 at%was the highest(206.2),and the response and recovery rate was very fast(0.5/1.4 s).