Figure 2. Hydrogen production from water using photocatalysts with two different PBG positions under UV light with flux about 1–1.2 mW/cm² and under direct sun light with UV flux of about 0.3–0.4 mW/cm².

It is to be noted that the Au/TiO₂ with the PBG position close to its electronic band gap is 2 to 3 times more active than an exactly similar material in all respects (except macroporosity and PBG properties) and where the PBG is far from the electronic band gap. Under direct sun light PBG materials are very active despite the lower UV flux. The highest performance was found for the Au-Pd/TiO₂ PBG 360 nm. (B). SEM images of the two PBG Au/TiO₂ photo-catalysts. Hydrogen production rates are given in (C).