Highly photocatalytic activity of nanocrystalline TiO2 (anatase, rutile) powders prepared from TiCl4 by sol-gel method in aqueous solutions.

•TiO2 nanopowders were successfully prepared.•The presence of the inorganic precursor in the synthesis of TiO2 improves crystallinity.•The optimum percentage of rutile is 4% in the TiO2 samples.•This study shows the balance between quality and photocatalytic efficiency.•Synthesized TiO2-600 degrades FA more rapidly than TiO2-P25.

In this piece of research, we have synthesized titanium dioxide (TiO2) powders from titanium tetrachloride (TiCl4) as an inorganic precursor by applying the sol-gel method. The effect of the calcination temperature in the range 400-800 °C on the photocatalytic performance of TiO2 nanoparticles was studied. The samples were characterized by TEM, BET surface area measurement, DRS and XRD. They were then used for the photodegradation of two model pollutants - phenol and formic acid - under exposure to UV-A radiation. Despite the fact that the adsorption of both phenol and formic acid on the various TiO2 nanomaterials followed the Langmuir model, their degradation kinetics followed the Langmuir-Hinshelwood model. The results emphasized a strong increase in the adsorption and in the photocatalytic activity with the TiO2 calcined at 600 °C which was nearly 1.5 times higher than that of TiO2-P25 in the case of formic acid. For the degradation of phenol, TiO2-600 had a similar activity as TiO2 P25. This is related to their tendency to degrade the intermediate products than the phenol itself. A formal mechanism scheme of phenol degradation has been proposed. The maximum photocatalytic efficiency was reached with the sample calcined at a temperature of 600 °C, while a further increase in temperature depleted the photocatalytic response.The highest photocatalytic activity of the sample calcined at 600 °C can be attributed to the improvement of the crystallization and the optimal anatase/rutile ratio (96/4).

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