Antimony Doping in SnO2 Nanoparticles for Sensitive NO2 Sensors

Developing cost-effective NO2 sensors with ppb-level limit of detection (LOD) is crucial for effectively monitoring this widespread toxic gas. SnO2, a promising candidate, suffers from limitations including poor selectivity, high operating temperature, and sensitivity to moisture. To address these challenges, we synthesized high-performance Sb-doped SnO2 sensors via a hydrothermal method. All SnO2 products exhibit rutile tetragonal crystalline structures and consist of fine nanoparticles, primarily in the several-nanometer range. It is found that dopant activation in the SnO2 lattice is dependent on both temperature and doping concentration with minimum resistivity achieved at optimal annealing temperature. For sensor fabrication, an annealing condition at 300 °C in ambient air for 2 h was chosen. All sensors demonstrated prominent selectivity toward NO2. The sensor response follows a volcano-shaped curve, with the 1.0 and 2.0 atom % Sb-doped sensors exhibiting the highest responses at room temperature (∼25 °C). This peak response shifts to the 0.1 and 1.0 atom % Sb-doped sensors at 75 °C. The optimal operating temperature for achieving the highest response progressively decreases with increasing Sb doping, while moisture resistance also improves. The SnO2:0.1%Sb sensor demonstrates the most impressive overall performance, exhibiting a higher response stability against temperature variation. It boasts an ultrahigh response of 2.65 × 104, rapid response/recovery times of 153 s/11 s to 1 ppm of NO2 at 75 °C, and a LOD down to 20 ppb. Density functional theory calculations suggest that moderate Sb doping level leads to stronger NO2 adsorption, explaining the observed optimal performance at moderate doping concentrations.