Fabrication, characterization and performance evaluation of zinc oxide doped nanographite material as a humidity sensor

Introduction. The growing demand for real-time environmental monitoring technologies has led to increased interest in high-performance humidity sensors with rapid response, high sensitivity, and long-term stability. Zinc oxide (ZnO) is a widely used semiconducting oxide material for such applications due to its chemical stability and sensitivity to humidity variations. However, its performance can be further enhanced through material engineering. This study investigates the doping of ZnO nanoparticles with nanographite material (NGM) to improve humidity-sensing characteristics. The purpose of the work is to develop ZnO–NGM nanocomposite-based capacitive humidity sensors with improved response/recovery time and sensitivity by modifying the electronic and surface properties of ZnO through NGM doping. Research methods. ZnO–NGM nanocomposites with varying NGM content (1 wt.%, 2 wt.%, 4 wt.%, 5 wt.%, and 10 wt.%) were synthesized via a chemical precipitation route. The optical behavior of pure ZnO was analyzed using UV–Vis spectroscopy, which revealed a sharp absorption edge at 367 nm, indicating a bandgap near 3.3 eV. Structural and morphological properties were examined using X-ray diffraction (XRD) and scanning electron microscopy (SEM), confirming NGM integration and enhanced surface porosity. The composite sensing films were deposited onto FTO-coated glass substrates using the ‘doctor blade’ method to fabricate the capacitive sensors. The sensing performance was evaluated in a nitrogen-controlled chamber over a relative humidity (RH) range of 10% to 95%, with capacitance measurements recorded across a frequency range of 10 kHz to 1 MHz. Results and discussion. Among all tested compositions, the 4 wt.% NGM-doped ZnO sensor demonstrated the best performance, with a rapid response time of 4.0 s, a recovery time of 6.2 s, and excellent sensitivity. These improvements are attributed to enhanced surface conductivity and more active adsorption-desorption kinetics due to NGM. The developed sensors show strong potential for integration in real-time environmental monitoring systems, industrial automation, and smart home humidity control applications. The incorporation of nanographite into ZnO matrices significantly enhances humidity-sensing capabilities. The ZnO–NGM composite, particularly at 4 wt.% doping, offers a promising pathway for the development of next-generation, high-efficiency humidity sensors.