Surface modification of sol-gel synthesized TiO2 nanoparticles induced by La-doping

The influence of La-doping in the range of 0.5-6.0 mol% on structural and morphological properties of TiO2 nanopowders synthesized by sol-gel routine has been investigated by XRPD, AFM, EDS and BET measurements, as well as Raman spectroscopy. The XRPD and Raman measurements have revealed the anatase phase as dominant in all nanopowders, with crystallite size decreasing from ~ 15 nm in pure TiO2 to ~ 12 nm in La-doped samples. The BET data suggest that all samples are fully mesoporous, with mean pore diameters in the range of ~ 6-8 nm. The specific surface area and the complexity of pore structure are greater in doped samples than in pure TiO2 sample. The spectroscopic ellipsometry has apparently shown that the band gap has been gradually increased with the increase of La content. The STM and STS techniques have been used successfully to evaluate the surface morphology and electronic properties of La-doped nanopowders. All investigated properties have been related to photocatalytic activity, tested in degradation of a metoprolol tartrate salt (0.05 mM), and induced by UV-radiation. All doped samples showed increased photocatalytic activity compared to pure TiO2, among which the 0.65 mol% La-doped sample appeared to be the most efficient.