Synthesis And H₂S Sensing Properties Of RGO/NiO Based Composite Nanofibers

With the rapid development of industry and economy,the emission of noxious gases such as H₂S,NO_X is obviously increasing.Therefore,the demand for high efficiency and rapid detection of toxic and harmful gases is becoming increasingly urgent.Metal oxide semiconductor gas sensing materials such as SnO_2,NiO have attracted much attention due to their advantages of low price and fast response-recovery speed.However,the single gas sensing material?NiO as an example?also has the disadvantages of poor selectivity and high working temperature,which restricts the practical application of NiO gas sensor in industrial production.Metal element doping and gas sensing material composite are the common methods to improve the gas sensing properties of metal oxide semiconductor materials.Graphene has been widely used in electrochemical energy storage,gas sensors and other fields because of its large specific surface area,strong electron transport ability and excellent gas adsorption ability.In order to improve the gas sensitivity of NiO based gas sensors to H₂S,this paper will study the composite of micro reduced graphene oxide?rGO?and NiO based on NiO nanofibers,and improve the gas sensing properties of NiO nanofibers by the synergistic effect of two components.On the basis of rGO/NiO composites,we further study the doping of NiO elements in the composites,and explore the improvement of the gas-sensing properties of rGO/NiO nanofibers by doping metal elements.The specific research work is as follows:1.The ratio of raw materials and reagents in the precursors for electrospinning and the influence of sintering process on the morphology are discussed.Among them,when the ratio of nickel acetate and PVP is close to 1:1 and the morphology of the NiO nanofibers is fine and uniform.The results showed that the sensitivity of NiO nanofibers to 10 ppm H₂S gas at 75?and 125?is2.52 and 1.58.2.The preparation and gas sensing properties of rGO/NiO nanofibers with different ratio?0,0.5 wt%,1 wt%,1.5 wt%?rGO compositions were studied.The results showed that there was no obvious effect on the morphology and crystal structure of NiO nanofibers.However,the gas sensing properties of composite nanofibers to H₂S have been improved significantly.Especially 1 wt%rGO/NiO composite nanofibers,its best sensitivity to 10 ppm H₂S gas at room temperature is up to 167.11,is 23.8 times that of pure NiO nanofibers.However,the recombination of rGO did not significantly improve the response time of NiO nanomaterials to H₂S gas.3.In order to further improve the gas sensing properties of NiO based nanofibers,NiO in the composites was doped with Al,Sn,and its morphology,structure,composition and gas sensing properties were studied.In this paper,an appropriate amount of aluminum salts?0,1 at%,2 at%,4 at%?and Sn salts?0,1 at%,3 at%,5at%?were added to the nanofiber precursor of 1 wt%rGO/NiO by electrostatic spinning,after the same spinning and sintering,The required 1 wt%rGO/Al-doped NiO nanofibers and 1 wt%rGO/Sn-doped NiO composite nanofibers were obtained.The composite nanofibers were characterized by SEM and XRD,and the gas sensing properties were tested and analyzed,it showed that although the morphology and structure of NiO based nanofibers doped with a spot of Al,Sn did not significantly alter compared with pure NiO nanofibers,However,the gas sensing properties of H₂S were improved obviously by doping with Al,Sn.The optimum doping molar ratio of Al is 2 at%and the best doping molar ratio of Sn is 3 at%.the optimum working temperature of both is 125?,The responsivity of 1 wt%rGO/2 at%Al-doped NiO nanofibers to 5 ppm H₂S gas reached 4.86,which is 3.07 times that of pure NiO nanofibers,and 2.08 times that of 1 wt%rGO/NiO composite nanofibers.Under the same conditions?125?,5 ppm H₂S?,the response of 3 at%Sn metal to 1 wt%rGO/NiO nanofibers to H₂S is 28.74,which is 18.19 times that of pure NiO nanofibers,and 12.25 times that of 1 wt%rGO/NiO composite nanofibers.For 1 wt%rGO/NiO composite nanofibers doped with Al,Sn,the gas sensitivity test results show that,Sn doping is more favorable to the improvement of gas-sensing properties of 1wt%rGO/NiO composites.4.In order to further improve the responsivity and response-recovery time of NiO based nanofibers at low temperature,Cu doping in the 1wt%rGO/NiO nanofibers were studied,after spinning and sintering,The 1 wt%rGO/Cu-doped NiO composite nanofibers were obtained.The results of SEM,TEM and XRD showed that there was no significant change in microstructure and morphology with the incorporation of Cu element.The gas sensing results showed that the Cu-doping greatly enhanced the gas sensitivity of the composite nanofibers to H₂S,The optimum working temperature is also reduced from 125?t o 75?,The responsivity of 1 wt%rGO/Cu-doped NiO nanofibers to 5 ppm H₂S gas reached 85.69,which is 34 times that of pure NiO nanofibers,and 13.69 times that of 1 wt%rGO/NiO composite nanofibers.Compared with the doping of Al and Sn,The Cu doping of 1wt%rGO/NiO composite nanofibers increases the responsivity obviously,decreases the working temperature,and decreases the corresponding-recovery time.