Photocatalytic performance of Au/ZnO nanocatalysts for hydrogen production from ethanol

• H2 was photocatalytically produced at a constant rate, from a water–ethanol mixture, using ZnO and Au/ZnO catalysts.
• Loading ZnO materials with gold increased the photoefficiency towards H2 production.
• Au/ZnO materials with variable morphology are obtained by a double impregnation method for gold loading.
• Gold nanoparticles size plays a major role in the photoefficiency of Au/ZnO materials.

Gold was loaded on several ZnO samples with different morphologies: needle-like (ZnO-n), flower-like (ZnO-f), rods (ZnO-r), and prepared by a thermal calcination process (ZnO-t). A commercial ZnO sample (ZnO-c) was also used for comparison. Bare ZnO and Au/ZnO materials were used for the photocatalytic production of H2 from a water–ethanol solution under UV–vis irradiation (λ > 300 nm). During the photocatalytic runs, hydrogen was generated at a constant rate for all samples, as well as CH4 and CO. The obtained results show that bare ZnO materials were able to promote H2 photogeneration, being ZnO-f the most efficient in terms of H2 generation. Loading with Au, in general, increased the photoefficiency for all materials. The most active gold loaded photocatalysts were the ones with the lowest gold nanoparticle sizes: Au/ZnO-f (427 μmol h−1 gcat−1; 5.4 nm) and Au/ZnO-n (280 μmol h−1 gcat−1; 5.8 nm). The samples with largest size (Au/ZnO-r and Au/ZnO-t with 6.2 nm, and Au/ZnO-c with 12.5 nm) were not so efficient (values below 230 μmol h−1 gcat−1). Au/ZnO-f seems to be the most promising photocatalyst, generating the highest amount of H2 and the lowest quantities of CH4 and CO. It is also possible that the intricate morphology of ZnO-f may scatter the incoming light, enhancing light absorption efficiency and increasing the photoefficiency of this material.

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