The Influence of Carboxyl-Functionalized Carbon Dots on Ethanol Selectivity in Gas Sensing

Abstract

For semiconductor tin dioxide (SnO2) materials, the oxygen adsorption theory often struggles to explain their selectivity towards specific gases. Therefore, it is worth considering altering the surface functional groups of SnO2 to modify its surface state and enhance its selectivity towards specific gases. Due to the rich functional groups on the surfaces of carbon dots, this study employed a hydrothermal method to prepare three types of carbon dots with varying carboxyl functional group contents by adjusting the hydrothermal time. These carbon dots were then used as dopants and combined with SnO2 to create composite gas-sensitive devices. The gas-sensing test results indicate that the introduction of carboxyl functional groups can enhance the selectivity of SnO2 towards ethanol. Furthermore, at any operating temperature within the range of 150–300 °C, the higher the carboxyl functional group content on the surface of carbon dot-doped SnO2, the higher the sensitivity towards ethanol. By employing density functional theory (DFT), the interaction energies between the surfaces of carbon dots and surface carboxyl groups with the target gas were calculated. These calculations validated the gas-sensing test results, confirming that the presence of carboxyl functional groups enhances the selectivity towards ethanol. The results of this study can provide new insights into the research on the selective mechanism of gas-sensitive materials.