Phosphorus doped TiO2 as oxygen sensor with low operating temperature and sensing mechanism

Nano-scale TiO2 powders doped with phosphorus were prepared by sol–gel method. The characterization of the materials was performed by XRD, BET, FT-IR spectroscopy, Zeta potential measurement and XPS analysis. The results indicate that the phosphorus suppresses the crystal growth and phase transformation and, at the same time, increases the surface area and enhances the sensitivity and selectivity for the P-doped TiO2 oxygen sensors. In this system, the operating temperature is low, only 116 °C, and the response time is short. The spectra of FT-IR and XPS show that the phosphorus dopant presents as the pentavalent-oxidation state in TiO2, further phosphorus can connect with Ti4+ through the bond of Tisingle bondOsingle bondP. The positive shifts of XPS peaks indicate that electron depleted layer of P-doped TiO2 is narrowed compared with that of pure TiO2, and the results of Zeta potential illuminate that the density of surface charge carrier is intensified. The adsorptive active site and Lewis acid characteristics of the surface are reinforced by phosphorus doping, where phosphorus ions act as a new active site. Thus, the sensitivity of P-doped TiO2 is improved, and the 5 mol% P-doped sample has the optimal oxygen sensing properties.