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.