Controllable growth of “multi-level tower” ZnO for biodiesel production

“Multi-level tower” ZnO with bulk quantity has been grown by a simple aqueous solution technique. Detailed structural characterization revealed that, the “multi-level tower” ZnO showed perfect hexagonal sectional morphology, with the length and diameter being 1–2 μm and 200–300 nm, respectively. When “multi-level tower” ZnO was used as the solid base catalyst to synthesize biodiesel, a biodiesel yield of 73.5% was achieved, much higher than the 46.2% of particle-like ZnO. Preferred nucleation and growth of ZnO nuclei along [0 0 0 1] direction resulted in hexagonal rod-like ZnO, and further layer-by-layer stacking of rod-like ZnO led to “multi-level tower” architectures, which predominantly exposed active O2− on (0 0 0 2), (1 0 1¯ 0), (0 1 1¯ 0) and (1¯ 1 0 0) planes of ZnO, resulting in obvious enhancement of catalytic activity and high yield of biodiesel.