rGO-WO3 heterostructured sensor for fast and selective NO2 detection with IoT-enabled air quality monitoring

In recent years, rapid advancements in digital connectivity and smart technologies have transformed the way devices interact and share information. The Internet of Things (IoT) plays a crucial role in advancing various fields, including Industry 4.0, Big Data, and machine-to-machine communication technologies. In this regard, a cost-effective approach for NO 2 gas sensor prototype comprising heterostructured rGO-WO 3 films have been developed. The hydrothermal growth of rGO conductive sheets on WO 3 nanoparticles formed a high-surface-area, loosely packed architecture which prevented WO 3 agglomeration and formed efficient charge-transport pathways, as confirmed by FESEM, EDX and XRD. Chemiresistive sensing tests of 1–200 ppm NO 2 at room temperature demonstrated a seven-fold response of rGO-WO 3 than pure WO 3 . The sensor demonstrates stable operation in elevated temperature environments up to 50°C, which can be attributed to enhanced surface reaction kinetics and improved adsorption–desorption dynamics at higher temperatures. At this optimized temperature, the sensor exhibited a significantly higher response of 781% toward NO 2 , compared to 86.3% for WO 3 alone. The selectivity test towards H 2 , NH 3 and CO 2 has shown no cross-sensitivity, proving that there is high selectivity towards NO 2 . After optimizing the sensing parameters, the composite sensor has been integrated into a prototype system with IoT capability. The device is interfaced with an Arduino Uno R3 and a SIM800A GSM Module to enable wireless communication and SMS-based alerts. The system is capable of detecting NO 2 gas in the environment and transmitting real-time data to a smartphone via a mobile hotspot, allowing remote monitoring and immediate notification.