Ionic liquid assisted synthesis of snowflake ZnO for detection of NOx and sensing mechanism

Ionic liquid [Bmim] [BF4] is used as a templating agent to synthesize ZnO with snowflake morphology by hydrothermal method. Different calcination temperatures make snowflake ZnO retain different content of ionic liquid residual which results in different gas response. The mesoporous ZnO material obtained after calcination at 650 degrees C shows the best gas response to NOx,. The sensor not only has excellent gas selectivity, but also exhibits an optimal response to NOx (S = 73.4) at 170 degrees C with a response range of 0.05 similar to 10 ppm. In addition, the sensor has good repeatability and long-term stability and also exhibits good moisture resistance at different humidity levels which may be attributed to an appropriate amount of residual ionic liquid after high temperature calcination. The reaction mechanism of the sensor to NOx is also discussed in detail based on XPS analysis, GC-MS measurement and DFT calculations.