Ehanced Gas Sensing Performances Of ZnO And Mechanism By Doping

Flower-like ZnO nanocrystals were successfully synthesized by a simple hydrothermal method in aquatic medium. The crystal structure was characterized by X-ray Diffraction (XRD) analysis. Fourier Transform infrared spectroscopy (FTIR) was used to further analyze the crystal structure. The morphology was observed by scanning electron microscopy (SEM). Furthermore, gas sensing performances of sensors based on flower-like ZnO were measured, the influence of annealing temperature and operating temperature on responses to different gases in different concentrations were measured. The intrinsic defects of ZnO annealed at different temperature were studied by room temperature photoluminescence (PL) analysis. Besides, the X-ray photoelectron spectroscopy (XPS) was used to analyze nonstoichiometry of ZnO crystals.In order to improve gas sensing performance of ZnO, ZnO was modified by doping using hydrothermal method. Al-doped flower-like ZnO nanocrystals and Fe-doped ZnO microflowers were synthesized. The changes in properties of the materials after doping were analyzed by a variety of characterization methods. The effect of metal doping amount on gas sensing performances was investigated by gas sensing measurement. Furthermore, the transient responses for different gas concentrations were simulated using Langmuir-Hinshelwood (L-H) reaction mechanism. The mechanism of enhanced gas sensing performances by doping was studied by means of adsorption and desorption of the gas on materials surface (chemical sensitization), PL and XPS analysis (electronic sensitization). The changes in band structures and densities of states for undoped and doped ZnO have been calculated using the first-principles based on the density functional theory (DFT).Cd-doped ZnO nanofibers were successfully synthesized by electrospinning followed by thermal treatment. The changes in crystal structure and morphology after doping were investigated by a variety of characterization methods. Besides, the influence of annealing temperature on particle size and specific surface were also analyzed using XRD and Brunauer-Emmett-Teller (BET). The gas sensing performances of ZnO annealed at different temperature and doped ZnO to CO were measured. Optimal Cd doping amount was obtained by gas sensing measurement. The change in band gap of ZnO with Cd doping amount were analyzed by UV-visible absorption spectrum (UV-Vis). The formation energy of undoped and doped ZnO was calculated using the first-principles.SnO2-CuO heteroj unction nanostructures were prepared by electrospinning technology. N-type semiconductor SnO2was modified by p-type semiconductor CuO.Optimal CuO amount was obtained by gas sensing measurement and the mechanism of enhanced gas sensing performances was also discussed in detail by p-n heterojunction.