Preparation of a La/N co-doped TiO2 film electrode with visible light response and its photoelectrocatalytic activity on a Ni substrate

To prevent the recombination of photoelectron–hole pairs and to extend the adsorption in the visible-light region, a TiO₂ coating co-doped with lanthanum and nitrogen on nickel foam was successfully prepared through sol–gel and dip coating methods using the precursors butyl titanate (TBOT) for Ti, lanthanum trioxide for La and urea for nitrogen. The photoelectrocatalytic properties of the prepared samples in the degradation of malachite green were examined under visible light. The phase composition, crystalline structure and optical properties of the La/N co-doped TiO₂(Ni) photo-electrodes were studied using different measurement methods, including XRD, SEM, UV–vis DRS, Raman and FTIR. The results indicated that the co-doped TiO₂(Ni) photo-electrode not only effectively restrained the growth of the TiO₂ grains, but also inhibited the transformation of the titania phase from anatase to rutile. The photo-response of the modified samples was substantially extended from 400 nm to 480 nm, and the band gap narrowed from 3.2 eV to 2.79 eV. The co-doped TiO₂(Ni) samples exhibited higher photocatalytic activity as a result of the synergistic effects of the La and N co-doping. The degradation rate of malachite green by the La_0.2%N_20%/TiO₂(Ni) photo-electrode was 23.5% higher than that of the un-doped sample; this result indicated that the extended range of responsive wavelengths greatly expanded the possible applications of the modified electrode. When a low bias voltage was applied to the La_0.2%N_20%/TiO₂(Ni) photo-electrodes, the electrodes exhibited even better photoelectrochemical properties and photoelectrocatalytic activity than a La_0.2%N_20%/TiO₂(Ni) film under visible light irradiation.