Synthesis, characterization, and photocatalytic activity of Au-ZnO nanopyramids

Nanocrystalline Au-ZnO heterostructures were synthesized using a wet-chemical process where single-crystalline ZnO grows along the [0001] direction on top of polycrystalline Au seeds. High resolution transmission electron microscopy finds a 3.5% expansion of the ZnO (002) plane at the heterostructure interface. Rietveld analysis of X-ray diffraction patterns from ZnO and Au-ZnO powders find that the crystallographic microstrain in the metal oxide is 0.047% and 0.146%, respectively, illustrating that the crystallographic expansion at the heterostructure interface is detectable by bulk characterization techniques. Broad-band photo-degradation studies with methylene blue find that the Au-ZnO heterostructures decompose the dye 6 times faster than pure ZnO. Wavelength-dependent photodegradation studies illustrate direct gap excitation of the ZnO component of the heterostructure is required to initiate dye decomposition. The mechanistic details leading to this photocatalytic activity are discussed.