| Metal oxide semiconductor gas sensor has become an important tool for gas detection and monitoring due to its advantages of fast response,small size and low cost.In recent years,a new type of material,metal organic framework,presents adjustable three-dimensional pore structure,which can form a porous and hollow structure while retaining the frame structure of the material,and is more conducive to gas absorption and electron transfer.Due to its special structure and excellent performance,metal-organic framework has attracted wide attention and provided a new research idea for gas sensing field.In this paper,Zn-Fe bimetallic-organic framework material,Au supported Zn-Fe bimetallic-organic framework material and Zn-Ni metal organic frame material were respectively prepared based on Zn-containing materials by introducing different organic ligands and simple solvent thermal/hydrothermal method.Then as the precursor,derivative materials were obtained by removing organic ligands through aerobic calcining.Then the morphology,crystal structure,element composition and valence state of the samples were systematically analyzed by means of various characterization methods?XRD,SEM,TEM,EDS and XPS,etc.?.Finally,the sensitive materials were made into gas sensing elements to test their gas sensitivity to toxic gases,and the corresponding gas sensitivity mechanism was described.The results of this paper are summarized as follows:?1?solvent hot method is used to synthesis of Zn-Fe bimetallic-organic framework materials and different content of Au load?load 1 mol%,respectively,2 mol%,3 mol%,4 mol%?of Zn-Fe bimetallic-organic framework materials.XRD,SEM,TEM and XPS characterization analysis shows that the size of synthesised Au-loaded Zn-Fe bimetallic-organic framework is about 200 nm.With this as the precursor,Au/ZnFe2O4/Fe2O3composite is formed after high-temperature aerobic calcining.?2?The influence of Au load on the gas sensitivity of Zn-Fe bimetallic-organic framework was studied.Results show that under the best working temperature 220?,2 mol%Au load after gas sensor in testing the concentration of 200 ppm of n-butyl alcohol in the response value can reach27.6,the response value is significantly higher than the same condition of pure phase sensor,response and recovery time for 6 s and 16 s respectively,the minimum detection limit up to 50 ppb,and significantly improve the selectivity of the sensor.The mechanism was analyzed:after 2 mol%Au loading,more active sites were provided for the sensitive material,and the electron transfer efficiency was improved,resulting in lower resistance.At the same time,the surface of the sensitive material absorbs more oxygen molecules,increases the depletion layer and resistance,reacts with more gases to be tested,and improves its gas sensitivity.?3?Zn-Ni bimetallic-organic framework structure?Zn:Ni=5:1,2:1,1:1,1:2,1:5?containing different proportions of Zn/Ni?molar ratio?was prepared by one-step hydrothermal method,and 3D flower-shaped ZnO/NiO derivative material was obtained by further high-temperature aerobic calcination.The gas sensitivity characteristics of Zn-Ni metal organic framework with different proportions were studied.The results showed that the best gas sensitivity effect was achieved when the molar ratio of Zn and Ni was 1:2,and the response value to 200 ppm ammonia gas was up to 34,which was significantly better than that of other proportions.When the molar ratio of Zn and Ni is 1:5,the resistance of ammonia gas is increased,which shows the opposite characteristics with other proportion contents.This is because the sensor is p-type due to the excessive Ni content.At the same time,the mechanism of ZnO/NiO composite structure with a molar ratio of 1:2 between Zn and Ni to improve the gas sensitivity of the sensor was analyzed,and the reasons for this result were as follows:?1?the high p-n junction content between ZnO/NiO,?2?a large number of NiO enhanced oxygen adsorption,?3?the number of oxygen vacancies increased by the replacement of Ni2+and Zn2+. |
PDF Full Text Request