It is therefore highly likely that Cu(I) formed during the photocatalytic cycle at a-TiO2-Cu SA can be re-oxidized to Cu(II) by H2O2, which explains the increased photodegradation activity of a-TiO2-Cu SA as compared to the Cu-free benchmark TiO2 material (Figure ). It is noted that also Cu(II) can be reduced upon reaction with H2O2, albeit with a relatively much lower rate constant (k = 4.6 × 10 2 M -1 s -1 ), hence Cu(I) can be, in the presence of H2O2 intermediate, formed also via a non-photochemical pathway