Li–N doped and codoped TiO2 thin films deposited by dip-coating: Characterization and photocatalytic activity under halogen lamp

•Li and N have a synergetic effect on photocatalytic efficiency of codoped TiO2 under halogen lamp.•(Li, N) dopants decrease the recombination rate of photogenerated e–h.•(Li, N) dopants induce an increase of the energy gap, Eg.•A decrease of crystallinity of the thin films seems to occur for high loadings of co-doping. Li-, N-doped and codoped TiO2 powders and thin films, deposited on glass substrate using dip-coating method and Ti(OBu)4 as precursor, were prepared and their structural properties were investigated using grazing angle X-ray diffraction (GXRD), Raman spectroscopy, time resolved luminescence, X-ray photoelectron spectroscopy (XPS), ground state diffuse reflectance absorption and scanning electron microscopy (SEM). Unlike the powder samples, thin films with the same composition and calcination temperature exhibited lower crystallinity degree along with the prevalence of the anatase phase. Ground state diffuse reflectance absorption studies carried on the nanopowders have shown that both the Li and N dopants led to an increase of the band gap. XPS studies revealed differences in the binding energy of N in the presence and in the absence of Li, which was explained in terms of a modification in the chemical environment of N when Li is introduced. The photocatalytic activity of the ensuing film toward the degradation of aromatic amine pollutant revealed a huge enhancement upon doping with N or codoping with N and Li. This behavior is probably provide by a charge-transfer-complex mechanism in which neither the photocatalyst nor the organic compounds absorbs visible light by itself. The improvement in the photocatalytic properties occurred simultaneously with the increase of the lifetime of the charge carriers whenever N and Li were introduced at a level 2%.