Investigation of Pristine and Thermal Treated Sepiolite as Chemiresistive Gas Sensing Materials

Sepiolite has the potential to be a gas-sensing material due to a unique layered structure and functional group on the surface of the material. Sepiolite was tailored to its structural shape and composition by thermal treatment. Sepiolite was thermally treated at 450 ºC and 700 ºC for 12 hours, respectively. Pristine and thermally treated sepiolite were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HR-TEM), energy dispersive x-ray (EDS), UV-Vis reflectance, Fourier transform infrared spectroscopy (FT-IR), and thermogravimetric analysis (TGA). XRD and SEM demonstrated morphological analysis, such as crystallinity and shapes of the materials, depending on the thermally treated temperature. FT-IR and TGA results showed the departure of the water molecule and hydroxyl group when increasing the temperature. Seven different concentrations of an oxidizing analyte (nitrogen dioxide) and reducing agents (acetone and ethanol) were measured by sepiolite driven chemiresistive gas sensors at three different operating temperatures. Normalized sensing responses for each analyte showed that differences in the sensing materials' structure and composition had an effect on their sensing abilities (selectivity and selectivity). The power law fitting based on sensing responses showed how an increase in the thermally treated temperature, operating temperature, and analyte concentration influenced not only the sensitivity but also the transition from the n-type semiconductor response to the p-type response.