Mechanism enhancing gas sensing and first-principle calculations of Al-doped ZnO nanostructures

Al-doped flower-like ZnO nanostructures have been synthesized by a facile hydrothermal method at 95 °C for 7 h. The structure and morphology of the product were characterized by XRD, FTIR and SEM analysis. The sensing tests reveal that the response is significantly enhanced by Al doping, and the 0.3 wt% Al-doped sample exhibits the highest response of 464 to 10 ppm CO at an operating temperature of 155 °C. A change of the structural defects in Al-doped ZnO is responsible for the enhancement of the sensing properties, which has been confirmed by the room temperature photoluminescence (PL) spectra and X-ray photoelectron spectroscopy (XPS). The response time is reduced disproportionately with the increase in CO concentration by modeling the transient responses of the sensor using the Langmuir–Hinshelwood reaction mechanism. The band structures and density of states for pure ZnO and Al-doped supercells have been calculated using first principles based on density functional theory (DFT). The calculated results show that the band gap is narrowed and the conductance is increased by Al doping, which coincides with the experimental results of gas sensing.