Photocatalytic activity of one step flame-made fluorine doped TiO2

• Fluorine doped TiO2 nanopowders are produced by Flame Spray Pyrolysis (FSP).
• Residual surface fluorine on TiO2 surface inhibits formic acid oxidation at pH 3.7.
• F-doping of TiO2 produces a beneficial effects in OH radicals formation at basic pH.
• Photocurrent performance of slightly F-doped TiO2 exceeds that of pure TiO2.
• Best photocurrent response is attained in KOH aqueous solution containing methanol.

The photocatalytic performance of a series of fluorinated TiO2 samples (F for O molar substitution ranging from 0 to 1.5 at.%) synthesized by flame spray pyrolysis (FSP) in single step is examined in relation to the results of several complementary characterization techniques, including BET, XRD, XPS and UV–vis analyses. While the rate of photocatalytic hydroxyl radicals production increased when the photocatalyst contained small amounts of fluorine, the rate of formic acid mineralization was maximum with flame-made pure TiO2, showing an activity even better than that of P25 TiO2 in experiments performed in the presence of the same photocatalyst amount. However, the reaction rate decreased with increasing the nominal fluorine content of the materials, as expected for reactions occurring by direct interaction of the substrate with photoproduced holes. On the other hand, incident photon to current efficiency measurements evidenced that the presence of fluorine in the photocatalyst is beneficial, 0.29 at.% effective F for O substitution in TiO2 leading to the best performing photocatalyst powder, in line with previous results obtained in photocatalytic hydrogen production from methanol steam reforming with similarly FSP-prepared TiO2-based materials also containing platinum nanoparticles.

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