The Role of In-Plane Oxygen Vacancy Defects in SnO₂ Nanoparticles for CH₄ Sensing.

The utility of different types of surface defects in SnO₂ nanoparticles (NPs) for the detection of low concentration (50 ppm) of methane (CH₄) at relatively low temperature of 50 °C is established. Chemically synthesized SnO₂ quantum dots are annealed in air and Ar environments at 800 °C to make two different sets of SnO₂ NPs. Variation in dimension, morphology and optical properties due to the annealing conditions are elaborated using X-ray diffraction, transmission electron microscopy and UV Visible spectroscopy respectively. Electron energy loss spectroscopy provides an insight of defect distribution in NPs. Detailed temperature dependent photoluminescence and the Raman studies allow understanding the interplay of in-plane oxygen and bridging oxygen vacancies in above two samples for low concentration CH₄ detection at low temperature. The sensor response was about 1-2% due to low operating temperature. The decisive role of in-plane oxygen vacancy to detect low concentrations of gas and utility of bridging oxygen vacancy for improved response at high temperature are further corroborated from the analysis of sensor response and Arrhenius type plots.