NO₂-Sensitive SnO₂ Nanoparticles Prepared Using a Freeze-Drying Method

The n-type semiconductor SnO₂ with a wide band gap (3.6 eV) is massively used in gas-sensitive materials, but pure SnO₂ still suffers from a high operating temperature, low response, and tardy responding speed. To solve these problems, we prepared small-sized pure SnO₂ using hydrothermal and freeze-drying methods (SnO₂-FD) and compared it with SnO₂ prepared using a normal drying method (SnO₂-AD). The sensor of SnO₂-FD had an ultra-high sensitivity to NO₂ at 100 °C with excellent selectivity and humidity stability. The outstanding gas sensing properties are attributed to the modulation of energy band structure and the increased carrier concentration, making it more accessible for electron exchange with NO₂. The excellent gas sensing properties of SnO₂-FD indicate its tremendous potential as a NO₂ sensor.