The effects of gold nanoparticles deposited on titanium dioxide on the photocatalytic oxidative degradation of two organic substrates, i.e.formic acid and the azo dye Acid Red 1, and on the parallel O₂reduction yielding hydrogen peroxide have been investigated under visible light irradiation. The method employed to reduce Au(III) to metallic gold in the preparation of Au/TiO₂ photocatalysts was found to affect their photoactivity, also by modifying the properties of TiO₂. The presence of gold on TiO₂ facilitates both the electron transfer to O₂ and the mineralization of formic acid, which mainly proceeds through direct interaction with photoproduced valence band holes. The so-formed highly reductant CO₂˙⁻ intermediate species may contribute in maintaining gold in metallic form. The controversial results obtained in the photocatalytic degradation of the dye were rationalised by taking into account that with this substrate, which mainly undergoes oxidation through a hydroxyl radical mediated mechanism, the photogenerated holes may partly oxidise gold nanoparticles, which consequently act as recombination centres of photoproduced charge carriers.

Semiconductors crystal facet engineering has become an important strategy for properly tuning and optimizing both the physicochemical properties and the reactivity of photocatalysts. In this review, a concise survey of recent results obtained in the field of specific surface-oriented anatase TiO₂ crystals preparation is presented. The attention is mainly focused on the fluorine-mediated hydrothermal and/or solvothermal processes employed for the synthesis and the assembly of anatase micro/nanostructures with dominant {001} facets. Their peculiar photocatalytic properties and potential applications are also presented, with a particular focus on photocatalysis-based environmental clean up and solar energy conversion applications. Finally, the most promising results obtained in the engineering of TiO₂ anatase crystal facets obtained by employing alternative, possibly more environmentally friendly methods are critically compared.