Two-dimensional Cd-doped porous Co3O4 nanosheets for enhanced room-temperature NO2 sensing performance

P-type Co3O4 has received ever-growing interest as a promising gas-sensing material due to the unique advantages of low-cost, earth abundance and considerable electrical conductivity at relatively low temperature. Herein, we designed and fabricated two-dimensional (2D) Cd-doped porous Co3O4 nanosheets through a microwave-assisted solvothermal method and subsequently in-situ annealing process. It is found that as-prepared 5 %-Cd-Co3O4-based gas sensor shows a significantly improved response value of 3.38 (Ra/Rg) and a relatively lower recovery time of 620 s for NO2 detection at room temperature (25 °C). Additionally, the sensor displays a wide detection range for NO2 detection low to 154 ppb (low theoretical limit of detection), outstanding selectivity compared with some volatile organic compounds, and excellent long-term stability for 6 months. The results of experiments and the corresponding Lewis acid-base theory reveal that the excellent room-temperature sensing performance is mainly promoted by the Cd dopant through a combined set of factors, including enhanced electronic conductivity, increased oxygen vacancy concentration and formed Co2+−O2− to improve NO2 adsorption. However, the further increased concentration of Cd2+ as Lewis acid sites will decrease the adsorption of NO2 that can benefit for improving recovery performance. Thus, the demonstration of such 2D Cd-doped porous Co3O4 nanosheets provides valuable insights for the p-type metal oxide semiconductor-based room-temperature gas sensors.