Heterojunction-Enhanced MOF-Derived Co ₃ O ₄ /In ₂ O ₃ Composite Material for a High-Selectivity and High-Sensitivity Gas Sensor of Low-Concentration <i>n-</i> Butanol Gas

By ball milling, In2O3 derived from calcined In MOF was combined with ZIF-67 to prepare a composite material x at% ZIF-67/In2O3 (x represents the atomic ratio of Co to In). x at% ZIF-67/In2O3 was coated on an Ag–Pd electrode, and after aging at 300 °C, a heterojunction Co3O4/ In2O3 gas-sensing material was obtained in situ. The sensor of 1.89 at% Co3O4/In2O3 exhibited the high response of 5334 to 10 ppm n-butanol gas at 240 °C, which is much higher than the responses of the sensors reported in the literature to 100 ppm n-butanol, and it is also significantly higher than the sensing properties of other Volatile Organic Compounds (VOCs) at 100 ppm, indicating that the sensor has good selectivity and sensitivity. Especially, the sensor has excellent antihumidity, with a response of up to 1529 even under the relative humidity of 80%. The enhanced performance of the gas sensor is attributed to the heterojunction formed by uniformly attaching Co3O4 nanoparticles to the surface of In2O3 through ball milling, as well as the large specific surface area of the Co3O4/In2O3 composite material derived from MOFs, which contain a large number of regularly arranged pores with pore sizes suitable for n-butanol gas. The p-n heterojunction promotes charge-transfer and carrier separation, improving electron transport efficiency. The larger the surface area, the more active sites there are, which is more conducive to generating more reactive species.