Trace NO₂ Detection in Ambient Air Using Co-Phthalocyanine-Modified Graphene Field-Effect Transistors

The sensitive detection of NO2 in air is crucial for controlling environmental pollution and protecting public health. Therefore, a simple and sensitive method for detecting NO2 must be developed. In this study, we fabricated phthalocyanine (Co, Cu, Ni, and H2)-modified graphene field-effect transistors (FETs) for NO2 detection at the parts-per-billion (ppb) level. Compared with other phthalocyanine-modified devices, the Co-phthalocyanine-modified graphene FET exhibited large voltage shifts in its transfer characteristics following the introduction of NO2 gas at the ppb level. The Dirac-point voltage shifts observed at each NO2 concentration tested were well fitted to the Langmuir adsorption isotherm, indicating that the Co-phthalocyanine-modified graphene FET was capable of quantitatively detecting NO2 at concentrations ranging from a few ppb to the sub-ppm level, corresponding to environmental standards. In addition, the Co-phthalocyanine-modified graphene FET demonstrated high selectivity for NO2 and maintained excellent sensing characteristics even after repeated use. The NO2-sensing performance of the Co-phthalocyanine-modified graphene FET was not significantly degraded in air (0–25% relative humidity (RH)), and the device could quantitatively detect NO2 with high sensitivity even in 40% RH air. Considering these results, the Co-phthalocyanine-modified graphene FET could enable the highly sensitive detection of NO2 at the ppb level in ambient air with humidity.