Characterisation, phase-stability and surface chemical properties of photocatalytic active Zr and Y co-doped anatase TiO2 nanoparticles

摘要

We report on the characterization, phase stability, surface chemical andphotocatalytic properties of Zr and Y co-doped anatase TiO2 nanoparticles prepared by homogenous hydrolysis methods using urea as precipitating agent. The materials were analyzed by scanning electron microscopy, X-ray diffraction, Raman spectroscopy, BET isotherm and BJH pore size distribution measurements. It is shown that Y and Zr ions replace Ti ions in the anatase TiO2 structures up to a critical total dopant concentration of approximately 13 wt%. The co-doped particles show increased phase stability compared to pure anatase TiO2nanoparticles. The anatase to rutile phase transformation is shown to be preceded by cation segregation and dissolution with concomitant precipitation of Y2Ti2-xZrxO7 and ZrTiO4. Co-doping modifies the optical absorption edge with a resulting attenuation of the Urbach tail. The band gap is slightly blue-shifted at high doping concentrations, and red shifted at lower doping concentrations. Formic acid adsorption was used as a probe molecule to investigate surfacechemical properties and adsorbate structures. It was found that the relative abundance ofmonodentate formate compared to bidentate coordinated formate decreases with increasing doping concentration. This is attributed to an increased surface acidity with increasing dopant concentration. Photodegradation of formic acid occurred on all samples. With mode-resolved in situ FTIR spectroscopy it is shown that the rate of photodegradation of monodentate formate species are higher than for bidentate formate species. Thus our results show that the trend ofdecreasing photo-degradation rate with increasing dopant concentration can be explained by the adsorbate structure, which is controlled by the acidity of the surface.