Controllable Synthesis Of Fe₂O₃ Based Composites And Their Room-Temperature H₂S Sensing Properties

Nowadays,people benifit from the advancement of the industrialization of human society,and also suffer from the problem of air pollution at same time.Hydrogen sulfide is one of the culprit causing air pollution,who damages human health and causes environmental problems such as acid rain.In addition,hydrogen sulfide gas is flammable and explosive gas under certain conditions,so it is important to realize the detection of hydrogen sulfide gas at room temperature.So far,metal oxide semiconductor is still the main force of sensing materials in gas detecting field.Among them,iron oxide-based materials have stood out due to their abundant source,convenient preparation,and low cost.However,iron oxide based materials have poor response to H2S at room temperature,which limits their further application.Therefore,attentions have been paid to realize iron oxide-based gas sensors with high response at room temperature.This paper is mainly based on the preparation modification of a-Fe2O3 materials derived from Prussian blue.The Prussian blue template is synthesized with different particle size.The defect structure of their thermal induced oxidation product,iron oxide,were further influenced by these templates with thermal induced oxidation.Loading SnO2 quantum dots give rise to the chemically adsorbed oxygen,and adjust mobility and concentration of carrier.Further loading of Pt quantum dots will take advantages of electronic sensitization and chemical sensitization.By combining different methods,we try to obtain iron oxide-based gas sensing materials with varied surface properties.The relationship between surface properties and the corresponding gas sensing properties is also investigated,which might have a certain guiding significance for related research.First,we present a dual anion source(DAS)method to prepare Prussian blue materials with different particle size.The DAS method adjusts the size of the products by simply adjusting the proportion of Fe(II)reactant.The particle size of Prussian blue products can be tuned from 100 nm to 1624 nn as the Fe(II)reactant proportion rises.Further characterization analysis show that the Fe(II)content in Prussian blue products are positively correlated with Fe(II)reactant proportion.We believe that the crystallization process of Prussian blue crystals is closely related to the composition of the product.Through in-situ UV spectroscopy and analysis of the morphology of intermediate products,we found that in the nucleation period,the nucleation rate of Prussian blue decreases with the increasing of Fe(II)reactant proportion,while the particle size of intermediate product will rise,indicating that the nucleus number will decrease with Fe(II)reactant proportion rise.During the following growth of the nucleus,with the assistant of PVP?the nucleus will follow the mesocrystal growth mechanism,and grow up by orderly agglomeration.When the PVP concentration is sufficient,products with less nucleus are more likely to form a highly ordered agglomerate with larger particle size.Subsequently,we prepared the ?-Fe2O3 with different sizes,through theraml induced oxidation of Prussian blue with different particle size.It is found that at 600 ?,Prussian blue will turn into iron oxide with cavity.However,smaller particles can be converted into?-Fe2O3 hollow microbox,while the largest particles are converted into a hollow structrue,which consist of a-Fe2O3 and y-Fe2O3.Further investigation suggests that Prussian blue will be first converted to O-Fe2O3 and ?-Fe2O3 during the heating process,and then gradually converted to the most stable a-Fe2O3.XPS and PL analysis confirm that the oxygen vacancy content will rise with the particle size increasing.Thermal analysis method prove that the increasing Prussian blue template give rise to the decompotion temperature.However,as the particle size increase,the heat release will first rise to a maximum and then decrease,indicating that the oversize Prussian blue template particles might result in insufficient oxidation,which further leads to an increase in the oxygen vacancy concentration.We also test the gas sensing performances of pure phase ?-Fe2O3 microboxes with different size.It was found that gas sensing properties also increased,as a result of growing oxygen vacancy concentration.As the particle size further increased,the gas sensing performances will decrease due to the descending specific surface areaThen,the ?-Fe2O3 microbox are modified with different concentrations of SnO2 quantum dots.It was found that when the loading was 10 wt%,the gas sensing performance of ?-Fe2O3/SnO2 reached the optimum value,about 2.5 times that of pristine ?-Fe2O3.Further analysis indicated that the gas-solid reactions on the surface of the material do not show obvious differences after loading the SnO2 quantum dots,but the chemical adsorbed oxygen concentration was significantly enhanced on the material surface.Therefore,this improvement in performance should be attributed to the heterojunction structure formed by?-Fe2O3 and SnO2.Further analysis shows that the formation of heterojunction structure not only promotes the adsorption and ionization process of oxygen moleculas,but also effectively regulates the concentration and mobility of carriers,and thus promotes the gas sensing properties of H2S at room temperature..Finally,Pt quantum dots are successfully modified on the surface of ?-Fe2O3/SnO2 composites by UV irradiation.The loaded Pt quantum dot are charaterized to be 3 nm,with good activity.The modification of Pt quantum dots significantly improves the gas sensing performances.The DRIFTS analysis indicated that the Pt loading did not change the products of the reaction,but the strong catalytic Pt quantum dots promoted the O2 adsorption and further ionized to form more active chemically adsorbed oxygen species on the surface.The chemisorbed oxygen generated on the surface of Pt will migrate to the surface of the surrounding oxide.As a resul,high-speed and rapid electron depletion will take place in the?-Fe2O3/SnO2/Pt sensor,and the chemical adsorption oxygen concentration on the surface of the material increases,which will significantly improve the H2S gas sensing performances under room temperature.