Low-Temperature NO2 Sensor Based on ZnO/MWCNT Heterostructures for Intelligent Agriculture

Developing miniaturized portable sensors for detecting NO2 at low temperatures in agricultural environments is crucial for enhancing nitrogen fertilizer utilization efficiency and preventing environmental pollution. This work successfully synthesized ZnO/MWCNT heterostructures using an in situ 2D electrodeposition method under direct current voltage, which demonstrated exceptional gas-sensing performance toward NO2 under both room and lower temperature conditions. The sensor demonstrates a 4-fold enhancement response to 10 ppm of NO2 compared to pristine ZnO sensors and exhibits a response of 98% to 1 ppm of NO2 at room temperature with a detection limit of 30 ppb. Even at −20 °C, it maintains a 5.1% response to 1 ppm of NO2. Notably, the unique nanosheet structure endows the heterostructure with reversible temperature sensing and high-temperature circuit-breaker characteristics, enabling the sensor to have the ability to alarm for temperatures above 50 °C. The incorporation of MWCNTs and the formation of the p–n heterojunction play a synergistic role in enhancing the gas-sensing performance. Moreover, we successfully detected NO2 emissions from nitrogen fertilizers using the ZnO/MWCNT heterostructure sensor, demonstrating its potential for integration with Internet of Things (IoT) technology to enable intelligent agricultural monitoring.