NO 2 -Sensitive SnO 2 Nanoparticles Prepared Using a Freeze-Drying Method.

The n-type semiconductor SnO 2 with a wide band gap (3.6 eV) is massively used in gas-sensitive materials, but pure SnO 2 still suffers from a high operating temperature, low response, and tardy responding speed. To solve these problems, we prepared small-sized pure SnO 2 using hydrothermal and freeze-drying methods (SnO 2 -FD) and compared it with SnO 2 prepared using a normal drying method (SnO 2 -AD). The sensor of SnO 2 -FD had an ultra-high sensitivity to NO 2 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 NO 2 . The excellent gas sensing properties of SnO 2 -FD indicate its tremendous potential as a NO 2 sensor.