Mesoporous ZnO nanorods array with a controllable area density for enhanced photocatalytic properties

Usually, a ZnO nanorods array exhibits a relatively small effective surface area due to its smooth surface and large area density (the number of ZnO nanorods per unit area). In this work, a mesoporous ZnO nanorods array with a small area density and a large effective surface area was successfully synthesized on the surface of fluorine-doped tin dioxide (FTO) glass using a facile solution process, with ethylene glycol (EG) and water serving as the mixed solvent and cadmium ions serving as an additives. The area density, aspect ratio and specific surface area of mesoporous ZnO nanorods array can be controlled by adjusting the concentration of cadmium ions in the EG-H₂O mixed solution. The obtained ZnO nanorods array was applied as the photocatalyst for the photodegradation of methylene blue (MB) and showed a good catalytic performance that was dependent on the area density, rather than the specific surface area. This may be because a smaller area density of nanorods array can facilitate the diffusion of MB molecules and thus provide a larger effective surface area for MB adsorption, despite a large difference in their specific surface area. Therefore, this work can provide a guidance for synthesizing nanostructures with good photocatalytic activity on the devices.