Rational fabrication of a g-C3N4/NiO hierarchical nanocomposite with a large surface area for the effective detection of NO2 gas at room temperature

High-performance and cost-effective NO2-based gas sensors of metal oxides that operate at room temperature (RT) are of immense importance. A design strategy of a three-dimensional hierarchical nanostructure formed by the combination of two-dimensional (2D) graphitic carbon nitride (g-C3N4) nanosheets that are decorated with nickel oxide (NiO) nanosheets (NSs) via a facile hydrothermal method has been investigated here. The as-fabricated nanocomposite (g-C3N4/NiO, NiCN) sensor showed high sensing performance toward NO2 gas with a maximal sensitivity of 25.4 to 50 ppm, fast response time (0.53 s) and quick recovery time (25.06 s). Furthermore, the optimized nanocomposite structure (NiCN-2) showed long-term stability (12 weeks), a low detection limit (10 ppb) and higher selectivity toward NO2 gas at RT. This exceptional sensing performance of the NiCN-2 sensor toward NO2 might be attributed to the unique 3D hierarchical structures with a large specific surface area (146.8 m2·g−1), highly porous surface, abundant defect sites, extended internal charge transfer between the p-n heterojunction and high adsorption and transportation rates in the nanocomposite sensor. This study provides a new strategy for the formation of heterostructures between metal oxides and g-C3N4 for excellent gas sensitivity and addresses the fabrication of highly potent gas sensors.