Light-Enhanced Gas Selectivity in SnO2–xFy Nanocrystals: Competitive Adsorption Driven by Carbon Chain Length, Isomerism, and Functional Groups

An attempt was made to explore the essence of gas selectivity and the miscellaneous reactive sites of stannic oxide, which were obtained by combining oxygen reduction with increasing fluorine and activated by light irradiation. The microstructure and gas-sensing performance of stannic oxide were analyzed using X-ray diffraction, Raman spectroscopy, atomic force microscopy, ultraviolet spectrophotometry, and an electrochemical testing system. The results show that the carbon chain length, functional group position, and functional group species of the measured gas determine the gas-sensing performance of the nanocrystalline SnO2–xFy precipitated from quaternary Zn–O–F–Sn amorphous films by designing the injection sequence of gas in time and space. For 100 ppm gas molecules, the gas response sequences of the SnO2–xFy films are methanol (42.57) > ethanol (30.14) > 1-propanol (15.63) > 2-propanol (12.36) > acetone (10.32). The alcohol gases are apt to be adsorbed on oxygen vacancies to reflect the higher response value and higher optimal temperatures (280 °C), while ketone gases prefer to be adsorbed at the active site produced by fluorine to reflect fast response/recovery speed and lower working temperatures (260 °C).