Heterostructures of hollow Co3O4 nanocages wrapped in NiO cilia for conductometric NO2 sensing at room temperature

Metal organic frameworks (MOFs) have drawn the spotlight in the field of gas sensing due to their miraculous geometrical and electronic structures, as well as simple and controllable self-assembly processes. Here, NiO@Co3O4 heterostructures to be synthesized using heating reflux method by vertically wrapping ultra-thin NiO cilia on the surface of hollow ZIF-67 nanocages and applying this as a template for thermal annealing. The unique hollow structure and rich mesoporous structure provide space for gas diffusion and carrier migration. The prepared NiO@Co3O4-350 sensor achieves a high response of 47.4 and exceedingly short response/recovery time (1.3 and 9.6 s) at room temperature, with a minimum detection limit of only 10 ppb and good selectivity, repeatability and long-term stability for NO2 gas. This work highlights the significance of morphology and structure for improving gas sensing performance, which sheds a thought-provoking light on the design and preparation of composite oxide sensors.