Dual-defect enhanced NO₂ sensing performance at low power consumption of ZnO-ZnTe core-shell nanorods via one-step controllable assembly

Surface defect engineering is considered as an effective strategy to improve the gas-sensitive properties of sensing materials. In this work, a dual-defective ZnO-ZnTe nanorod composite without calcination is prepared via a one-step hydrothermal method. The nanorods are assembled by ZnTe coated ZnO with the diameter of ∼24 nm and the ZnTe shell thickness of ∼3 nm. The ZnO-ZnTe composite exhibits the response of 8.78–10 ppm NO₂ at 133 °C. Compared to the pure phase of ZnO and ZnTe, the composite exhibits a substantially improved response to NO₂ and it is able to recover within 70 s. The lowest detection limit of the sensor is 50 ppb. The composite has a significant advantage in terms of operating temperature and the lowest detectable concentration among similar sensors. The improved response of the composite is resulted from the presence of Zn defect (V_Zn) and O defect (V_O) in the composite, which increase the electron concentration of conduction band and expose more active sites for NO₂ surface adsorption. The effect of defect kinds on the response of the composite is also investigated in depth with the aid of DFT theoretical calculations combined with other characterization results.