Study On Structure Regulation And Room-Temperature NO₂ Sensing Performances Of Tin Oxide Modified Reduced Graphene Oxide Hybrids

As a common poisonous pollutant,NO₂not only has detrimental impact on human health,but it is also one of the main causes of severe environmental problems such as acid rain,photochemical smog.Therefore,it is crucial for determining the accurate concentration of NO₂in the atmosphere.In recent years,graphene-based resistive room-temperature NO₂sensors have developed rapidly,providing a new platform for detecting NO₂.Although the use of semiconductor oxides to regulate the surface structure of graphene has to some extent improved the sensitivity of graphene-based room-temperature NO₂sensors.The low sensitivity is still the bottleneck hindering the development of this kind gas sensors.Because the number of adsorption sites on the surface of sensing materials is fewer and the activity of adsorption sites is weak.In order to improve the sensitivity of graphene-based room-temperature NO₂sensors,this work has employed SnO₂modified reduced graphene oxide hybrids（SnO₂-RGO）as a research objective to develop surface/interface structure regulating methods for improving the sensitivity of the NO₂sensors.In this work,systematic investigations are carried out from the design and regulation of graphene-based gas sensing materials,fabrication and performance test of sensors,the analysis and discussion of gas sensing mechanism.And some meaningful results have been achieved.The main research contents of this dissertation include:1.An organic amine etching method is applied to regulate the surface structure of SnO₂-RGO,thereby improving the sensitivity of graphene-based room-temperature NO₂sensors.SnO₂-RGO with abundant oxygen vacancies（EA-SnO₂-RGO）is prepared via ethanolamine liquid phase etching method.After ethanolamine etching,not only the particle size of SnO₂in the composite material is reduced,but also oxygen vacancies are introduced on the surface of SnO₂particles.SnO₂in EA-SnO₂-RGO exhibits higher surface defects and smaller particle sizes after ethanolamine etching.The response value of the gas sensor to 1 ppm NO₂is increased to 5.8 at room temperature.2.A sensitized strategy combining noble metal sensitization and oxygen vacancy regulation has been developed to improve the sensitivity of graphene-based room-temperature NO₂sensors.Pd NPs modified SnO₂-RGO with abundant oxygen vacancies（Pd-SnO₂-RGO-V_O）is prepared through simultaneously loading palladium nanoparticles（Pd NPs）and introducing oxygen vacancies on the surface of the SnO₂-RGO served as matrix material by using wet chemical surface deposition and in-situ chemical reduction methods.The response value of Pd-SnO₂-RGO-V_Otowards 1 ppm NO₂is increased from 3.3 to 9.8 at room temperature,which is mainly due to the synergistic effects of heterojunction structure formed between Pd NPs and SnO₂,the catalytic activity of Pd NPs,and the activation of oxygen vacancies.3.A method for improving the sensitivity of graphene-based room-temperature NO₂sensors by using dual semiconductor oxide co-modification strategy is proposed.GO and simple inorganic salts are applied as precursors,SnO₂NPs andα-Fe₂O₃NPs co-modified graphene composites（α-Fe₂O₃/SnO₂-RGO）are prepared by adopting one-step hydrothermal method.The formation of multiple heterostructures in ternary composite systems not only optimizes the surface structure of sensing materials,but also reduces the band gap width of sensing materials.Compared to SnO₂-RGO,the response ofα-Fe₂O₃/SnO₂-RGO has a 2.5-fold increase towards 1 ppm NO₂at room temperature.4.A sensitized method based on the synergistic effect of noble metal sensitization and dual semiconductor oxides co-modification strategy has been developed to improve the sensitivity of graphene-based room-temperature NO₂sensors.Based on the work in the previous chapter,α-Fe₂O₃/SnO₂-RGO is used as the matrix material,and noble metals such as gold（Au）,palladium（Pd）and platinum（Pt）are used to modify its surface to further regulate the microstructures of the composite materials.The response value of Pt NPs loadα-Fe₂O₃/SnO₂-RGO（Pt-FSR）to 5 ppm NO₂reaches to 21.3 with the contribution of the excellent catalytic activity of Pt NPs.