Sonochemical synthesis of ZnO nanoparticles and its use as photocatalyst in H2 generation

ZnO was synthesized by a sonochemical method and it was used as photocatalyst for hydrogen generation. The physical properties of ZnO that had a major influence in the H-2 production were high surface area and low particle size. Furthermore, the effect of the oxygen vacancies in H-2 production was evaluated through the analysis of the ratio of the intensities of the (0 0 2) and (1 0 0) planes, and it was observed that when this ratio was higher than 1, a low photocatalytic activity was obtained. This fact was evidenced by the analysis of HRTEM images, which showed that ZnO sample with the highest H-2 production presented a higher amount of (1 0 0) crystal planes and a lower amount of (0 0 2), which confirms the relation observed by XRD. A lower amount of (0 0 2) planes was related to a higher amount of oxygen vacancies on ZnO surface. Thus, when ZnO was used as a photocatalyst in H-2 production, the presence of oxygen vacancies in its surface had a detrimental effect in the activity due to the photocorrosion phenomenon in ZnO. The highest photocatalytic hydrogen production was 107 mu mol g(-1) h(-1). The solar-to-hydrogen efficiencies obtained were higher (0.65%) than the reported values for ZnO and other simple oxides in these applications.