| Metal oxide semiconductors have good gas sensing properties.However,high working temperature(200?600?)hinders its development and also brings security risks.Quantum dots are a kind of quasi-zero-dimensional material,and they have become one of the ideal gas sensing materials for room temperature detection by virtue of their small size,large specific surface area and high activity.However,due to its poor carrier transmission capacity,it cannot play its advantages of high surface activity,resulting in poor sensor performance.Two-dimensional graphene with large specific surface area and high carrier mobility is used to adsorb gas and as carrier transport materials in gas sensors.3D porous structure has been widely used in gas sensors recently due to its larger specific surface area and good porous structure.Accordingly,in this paper,three-dimensional graphene was prepared by electrostatic adsorption using positively charged polystyrene microspheres(PAS microspheres)as template,and tin oxide quantum dots were prepared by solvothermal method.The main research contents and conclusions of this paper are as follows:(1)Graphene oxide was prepared by the optimized Hummers method with natural graphite flakes as the precursor.The positively charged microspheres(PAS microspheres)were prepared by the amination of polystyrene microspheres(PS microspheres).Based on the electrostatic adsorption mechanism,a negatively charged graphene oxide(GO)dispersion with a concentration of 72 mg/mL was selected to enwrap on the surface of the three-dimensional template PAS microspheres.Finally,the PAS template was removed to obtain pure three-dimensional porous graphene(3D rGO).When 3D rGO was applied to the methylene blue(MB)adsorption experiment,the MB degradation rate could reach 98%at 60 min,which was 18%higher than that of reduced graphene oxide(rGO).When 3D rGO was applied to the detection of nitrogen dioxide(NO2)gas,the sensitivity of 3D rGO to NO2 gas at 50 ppmincreased from 3.5 to 8.0,the response time decreased from 56 s to 12 s,and the recovery time decreased from 132 s to 80 s.(2)SnO2 quantum dots were prepared by solvothermal method,and the synthesis conditions of SnO2 quantum dots were studied.Transmission electron microscope(TEM)analysis results showed that the size of 2-3 nm controlled withen the ideal exciton Bohr radius were obtained when the reaction temperature was 180? and the growth time was 180 min.x-ray photoelectron spectroscopy(XPS)results showed that there was only the binding energy of Sn(?)and O-Sn(VI)in the sample,which proved that the sample was pure SnO2.SnO2 quantum dot solution and 3D graphene solution were mixed in a magnetic stirrer for 24 h to obtain SnO2 quantum dot/3D graphene composite.TEM showed that SnO2 particles were uniformly distributed on the surface of graphene,and no SnO2 agglomeration was observed.Three elements C,Sn and O were found in EDS spectra,which confirmed the successful preparation of the composites.(3)SnO2 quantum dot monomer material and SnO2/3D rGO composite gas sensor were prepared by spin coating at room temperature.Scanning electron microscope(SEM)showed that the morphology of SnO2/3D rGO composite film became loose and porous compared with SnO2 quantum dot monomer film.The gas sensing properties of the two materials were studied.The results showed that when the concentration of NO2 is 50 ppm,the response value of SnO2 quantum dot monomer material is 12.02,the response value of composite material is 66.03,and the performance of the latter is improved by 54.01.The response-recovery time of SnO2/3D rGO composite to 3 ppm NO2 decreased from 49 s and 85 s of SnO2 monomer material to 5 s and 7 s.In addition,the two gas sensors had good gas sensing selectivity for NO2 in the detection of SO2?NH3?CH4 and NO2 gases,and showed excellent performance in the repeatability and stability detection of 50 ppm NO2. |
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