Trace-level detection of nitric oxide triggered by the heterojunction synergy and mixed valence Co2+/Co3+ in Co3O4/NiTiO3

Accurate detection of nitric oxide (NO) at parts-per-billion (ppb) levels is critical due to its adverse effects on human health, even at trace concentrations. This study presents the design and evaluation of Co 3 O 4 -loaded NiTiO 3 nanostructures for ultra-low concentration NO sensing. The nanostructures were synthesized via microwave-assisted hydrothermal method, yielding a hierarchical architecture of Co 3 O 4 nanoflowers uniformly distributed on NiTiO 3 rods. The optimized 2 wt% Co 3 O 4 /NiTiO 3 sensor displayed high sensitivity to NO in the 5–100 ppb range, at an optimal operating temperature of 200 °C, with a low detection limit (LoD) of ∼0.22 ppb, and rapid response/recovery times. The sensor displayed a remarkable stability over 90 days with only ∼15 % deviation in response and demonstrated robust performance under humid conditions (10–75 % RH). NiTiO 3 serves as a chemically stable backbone of the sensor, offering a high-resistance baseline and abundant active sites for oxygen adsorption. Co 3 O 4 modification significantly enhanced gas response by forming p–n heterojunctions, reducing resistance, and facilitating charge transfer. Additionally, mixed valence Co 2+ /Co 3+ and Ti 3+ /Ti 4+ , along with increased oxygen vacancy concentration, significantly improved surface catalytic activity. These structural and electronic features synergistically promoted efficient NO oxidation, contributing to superior sensing performance. • Co 3 O 4 loaded NiTiO 3 perovskites synthesized via a two-step microwave-assisted hydrothermal method. • Mixed valence Co 2+ /Co 3+ and Ti 3+ /Ti 4+ and oxygen vacancies, improved the surface catalytic activity. • Synergistic Co 3 O 4 /NiTiO 3 heterojunction improves charge transfer efficiency. • Sensitivity to NO in the 5–100 ppb range. • Remarkable repeatability and long-term stability over 90 days.