Preparation, characterization and photocatalytic performance of noble metals (Ag, Pd, Pt, Rh) deposited on sponge-like ZnO microcuboids

• Novel sponge-like ZnO microcuboids were synthesized via an alcoholic thermal process.
• ZnO microcuboids have a hierarchical structure and a high surface area.
• The effect of noble metals on the photocatalytic activity of ZnO decreased in the order Pd>Ag>Pt>Rh.

Novel sponge-like ZnO microcuboids with a hierarchical structure were fabricated via an alcoholic thermal process. Then a series of noble metals (Ag, Pd, Pt, Rh) was loaded onto the microcuboids. The samples obtained were characterized by nitrogen physical adsorption, powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectroscopy (DRS), and X-ray photoelectron spectroscopy (XPS). The results show that the ZnO microcuboids have a high surface area and a sponge-like hierarchical structure. Activity tests for the degradation of acid orange II dye showed that the noble metals enhanced the activity of ZnO to different extents. For loading of 0.5 wt.%, the activity enhancement decreased in the order Pd>Ag>Pt>Rh. Co-loading of Pd and Ag had a detrimental effect on activity compared to single loading. The enhanced photocatalytic performance can be attributed to an increase in the rate of separation of photogenerated e–/h+ pairs induced by the noble metals.