Hybrid ZnO:Graphene Nanostructures for Selective NO Detection under UV Illumination at Room Temperature

Abstract

This study investigates the development of ZnO:graphene (ZnO:Gr) hybrid nanostructures for high-performance gas sensing at room temperature under 365 nm UV illumination. The graphene content was systematically varied to elucidate its synergistic role in modulating both sensing response and selectivity. Structural and spectroscopic analyses (XRD, SEM, and Raman) confirm the formation of a robust 0D/2D heterostructure characterized by strong interfacial coupling and induced lattice strain, while preserving the hexagonal wurtzite ZnO phase. Electrical characterization reveals a percolation-driven transition in charge transport, where the transition from ZnO-dominated to graphene-dominated conduction occurs near the 1.0–2.5 wt% threshold. Intriguingly, the ZnO:Gr hybrids exhibit a unique p-type-like sensing response, characterized by a resistance increase upon exposure to both reducing and oxidizing gases. This anomalous behavior is attributed to an interface-controlled mechanism, where the ZnO nanoparticles act as "molecular gates" that modulate the hole-carrier density and scattering effects within the graphene network. The optimized ZnO:Gr-1.0% sensor demonstrates exceptional performance toward NO gas, achieving a remarkable response of 1120% at 14.3 ppm – a 20-fold enhancement over pristine ZnO – along with an ultra-low detection limit of ∼14 ppb. These findings offer significant insights into interfacial engineering for designing high-sensitivity, low-power, room-temperature gas sensors for advanced environmental monitoring.