Ozone Differentiated Sensitization of TMO-SnO ₂ Sensors for Indoor Air Pollution Monitoring

Metal oxide semiconductor (MOS) gas sensors are promising in indoor air pollution monitoring, which however are still struggling to balance sensitivity and selectivity. In this study, transition metal oxide (TMO) modified SnO2 sensing materials are synthesized through a simple coprecipitation method. The sensitivity and selectivity are both modulated by ozone toward the typical indoor air pollutants, such as p-xylene and formaldehyde as analytes and ethanol as an interferent. The TMO modification enriches surface active sites, resulting in a nearly 5-fold performance enhancement versus pristine SnO2. Ozone thickens the electron depletion layer (EDL) to amplify the change of conductivity signal and deeply oxidizes the residual intermediates on the surface, making the electron transfer more significant compared to that in air. All of these contribute to lowering the optimal operating temperature for p-xylene, doubling the response to 5 ppm from 7.18 (300 °C, air) to 16.73 (260 °C, ozone) with a limit of detection (LOD) of 35.98 ppb, while the performance in formaldehyde detection is the opposite. The differentiated amplification between various analytes and interferents improves the accuracy of the array for p-xylene with a relative mean absolute error (RMAE) of less than 5%. This optimization strategy offers new insights into material regulation and gas interaction.