Low-Temperature NO ₂ Sensor Based on ZnO/MWCNT Heterostructures for Intelligent Agriculture

Developing miniaturized portable sensors for detecting NO 2 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 NO 2 under both room and lower temperature conditions. The sensor demonstrates a 4-fold enhancement response to 10 ppm of NO 2 compared to pristine ZnO sensors and exhibits a response of 98% to 1 ppm of NO 2 at room temperature with a detection limit of 30 ppb. Even at −20 °C, it maintains a 5.1% response to 1 ppm of NO 2 . 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 NO 2 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.