Graphene Dot-ZnO Hybrid Nanostructures as High-Performance Chemiresistive Sensors for H₂S Detection

The development of sensitive, selective, and low-cost gas sensors for hazardous pollutants remains a crucial challenge in environmental monitoring. Among gaseous pollutants, hydrogen sulfide (H₂S) has been shown to negatively influence ecosystem dynamics. The novelty of this study lies in the synergistic integration of graphene dots (GDs) with ZnO, which significantly enhances the sensing performance while enabling efficient operation at a reduced temperature. The synthesized materials were comprehensively characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy, UV-visible spectroscopy, Raman spectroscopy, photoluminescence spectroscopy (PL), dynamic light scattering (DLS), and thermogravimetric analysis, confirming the successful formation of the GD-ZnO hybrid structure. The fabricated thick-film sensors, tested in the 0.125-4 ppm of H₂S concentration range, exhibited an optimal operating temperature of 200 °C and a linear and fast response with a good sensitivity and recovery time. Compared to pure ZnO, the GD-ZnO composite in a 1:1 ratio not only demonstrated higher sensitivity and selectivity toward H₂S but also achieved efficient gas detection at a significantly lower operating temperature. The GD-ZnO (1:1) composition demonstrated the best performance, showing excellent repeatability, stability, and discrimination against interfering gases, such as CO, SO₂, NO₂, and H₂. Overall, the enhanced sensing performance, characterized by a sensitivity of 2.8582 × 10^-3, low operating temperature, and reliable response-recovery behavior, highlights the strong potential of the GD-ZnO nanocomposite for practical implementation in compact, low-power, and cost-effective H₂S monitoring devices for environmental and industrial safety applications.