Supercritical CO ₂ ‐Induced Defect Engineering in 2D SnO ₂ /rGO Heterojunction for Enhanced Ethanol Sensing at Room Temperature

ABSTRACT In response to the growing demands for social development and environmental monitoring, there is an urgent need for next‐generation miniaturized wireless volatile organic compounds (VOCs) sensors capable of detecting trace VOCs at parts‐per‐billion (ppb) levels under low‐temperature conditions. This work employed supercritical CO ₂ technology to fabricate a tin dioxide/reduced graphene oxide (SC‐SnO ₂ /rGO) heterojunction for developing a highly selective chemical sensor operable at room temperature. At 23°C, the sensor exhibits response/recovery times of (27.1 s/37.2 s @ 6 ppm) for ethanol and (18.7 s/20.3 s @ 6 ppm) for methanol at 6 ppm concentration, with theoretical detection limits of 9.85 ppb and 42.29 ppb, respectively. The enhanced performance is primarily attributed to the p‐n heterojunction between SnO ₂ and rGO, which facilitates efficient charge carrier migration. Additionally, supercritical processing modified the material's surface chemistry by increasing oxygen vacancy concentration, thereby significantly enhancing responsiveness to ethanol and methanol. DFT calculations provide a mechanistic explanation for the stronger ethanol adsorption energy (−1.077 eV) and enhanced charge transfer at the SC‐SnO ₂ /rGO interface. This study presents a viable material strategy and technical pathway for developing scalable, low‐cost VOC sensors capable of high‐selectivity operation at room temperature.