Evaluating the doping effect of Fe, Ti and Sn on gas sensing property of ZnO

Fe-, Ti-, Sn-doped (1.8, 7.4 and 3.4 mol% respectively) and pure ZnO are prepared by hydrothermal method using 10 mol% precursors, whose gas sensing property is studied using formaldehyde as the probe. The results show that the maximum response of pure ZnO to 205 ppm formaldehyde is ∼43 (at relative humidity 70 ± 10%) at 400 °C. But the gas response maxima shift to 300 °C for Fe–ZnO (∼52–205 ppm) and Sn–ZnO (∼140–205 ppm), and to 200 °C for Ti–ZnO (∼26–205 ppm). Beyond the maxima, the response of Fe–ZnO is lower than that of pure ZnO, while that of Sn–ZnO is always higher. The morphology, crystal structure, vibration modes, bandgap and crystal defects are studied to investigate the different doping effects on gas sensing property of ZnO. The results show that the secondary phase identified by X-ray diffraction and Raman spectra, and the crystal defects detected by photoluminescence might account for the different sensing behaviors.