Gas Sensing Property And In Situ DRIFITS Analysis Of Gas-solid Interface Of γ-Fe₂O₃-based Gas Sensors

Electrons transfer and acquisition between materials and tested gases, whichleads to resistance variation of materials, is the gas sensing mechanism of metal oxidesemiconductor gas sensors. As we all know, in situ DRIFTS is an effectivecharacterization method of surface interaction process, which is widely used in thegas-solid interaction mechanism research. Moreover, the research of gas-solidinterface reaction process and adsorption on materials is significant to the study of gassensing mechanism. In this paper, in situ DRIFTS was used to the characterization ofthe gas-solid interface reaction process and adsorption on γ-Fe₂O₃-based gas sensingmaterials at various working temperatures. The purpose was trying to build therelationship between the gas-solid interface reaction and gas sensing mechanism. Themain research work is shown in the following.（1） γ-Fe₂O₃films were printed on Al₂O₃ceramic chips by using screen printingtechnique. XRD and FSEM results indicated that porous γ-Fe₂O₃films were consistedof nano-spherical particles. The crystalline structure of the films was cubic γ-Fe₂O₃.The gas-solid interaction process and surface adsorbate species of formaldehyde andethanol on γ-Fe₂O₃films were characterized by in situ DRIFTS in time. The resultsshowed that the main surface adsorption species of ethanol gases on γ-Fe₂O₃wereacetate, formate and ethoxide species. Formate, dioxymethylene and molecularformaldehyde adsorbate were the main surface interaction species of formaldehyde. Inthe end, the gas-solid interface reaction mechanism was put forward in this chapter.（2） High gas sensitive performance double layers γ-Fe₂O₃/ZnO composite filmswere prepared by screen printing process combined with hydrothermal treatment. Gassensitivities to200ppm formaldehyde and200ppm ethanol was measured, the resultsproved that the gas sensitivity of double layers γ-Fe₂O₃/ZnO films was higher thanthat of pure γ-Fe₂O₃. In situ DRIFTS was utilized to detect the surface interaction ofreduced gases formaldehyde and ethanol on γ-Fe₂O₃/ZnO films. Gas sensingmechanism of γ-Fe₂O₃/ZnO to formaldehyde and ethanol was also explained.（3） In order to further improve the gas sensitivities of γ-Fe₂O₃gas sensors, Sn⁴⁺ modified γ-Fe₂O₃films were obtained by micro-injecting technology. Sn⁴⁺dopedγ-Fe₂O₃films possessed the best gas sensing performance to formaldehyde andethanol in the γ-Fe₂O₃-based gas sensors. In situ DRIFTS results showed that the mainsurface adsorption species of200ppm formaldehyde and200ppm ethanol on thedouble films were markedly unchanged. However, the intensity of the peaks related tointerface adsorbate species was varied. According to the analysis, the Debye length ofγ-Fe₂O₃was increased due to the doped Sn⁴⁺, and that the acid sites-(Sn⁴⁺-O2-)-,Br nsted acid, surface adsorbed O-on the surface of Sn⁴⁺doped γ-Fe₂O₃films werealso enriched. These synergistic effects may lead to the improved gas sensitiveperformance of Sn⁴⁺doped γ-Fe₂O₃films and played an important role in thegas-solid interface reaction.