Highly-enhanced toluene gas-sensing behavior of high-valent metal-cations doped Co3O4 nanostructures derived from ZIF-67 MOF

In this paper, the different valent metal-cations (Zn2+, In3+ and Zr4+) doped porous Co3O4 nanostructures were synthesized through the pyrolysis of ZIF-67 metal–organic framework (MOF). The influence of the different valence and doping content of metal-cations on the morphology, microstructures and gas-sensing performance of Co3O4 sensors is discussed in detail. The Zr-doped Co3O4 nanostructures present the higher specific surface area for the smaller average grain size, and the toluene gas-sensing performance of Co3O4 nanostructures is significantly improved with the high-valent Zr-doping. The high valence Zr-doping greatly improves the toluene gas-sensing properties, which Co2.717Zr0.189O4 sensor exhibits the highest response value of 94.58 to 100 ppm toluene gas (3.8-fold of Co3O4 sensor). The donor Zr-doping to p-type Co3O4 nanostructures optimizes the hole distribution and further affects Fermi level. Combining with the more oxygen adsorption from the high specific surface area, the resistance in air greatly decreases and resistance in toluene gas increases.