Low-temperature solution synthesis of a ZnO nanorod array with a mesoporous surface mediated by cadmium ions

Abstract

A ZnO nanorod (NR) array grown on a substrate by a wet chemical method usually exhibits a single crystalline nature and smooth surface which cannot adsorb a large amount of dye molecules. Thus, surface modification is necessary for a ZnO NR array in its photocatalysis application. In this work, a mesoporous structure has been introduced into the surface of a ZnO NR array via a facile chemical bath method mediated by cadmium (Cd) ions at 80 °C and subsequent calcination. During the growth process of the ZnO NR array, Cd ions can react with NH₃ molecules and OH⁻ ions in the growth solution to form Cd complexes and prefer to adsorb on the neutral {10-10} surface of ZnO NRs rather than on the positive (0001) facets due to face-selective electrostatic interactions. This will probably cause the formation of Zn(C₂H₃O₂)₂(C₂H₈N₂) which can be decomposed into ZnO nanoparticles after calcination, leading to the production of mesopores on the {10-10} surface of ZnO NRs. Also, the pore density and aspect ratio of the ZnO NR array with mesoporous surface are controlled by adjusting the Cd ion concentration and reaction temperature. The mesoporous ZnO NR array exhibits enhanced photocatalytic properties for the degradation of a methylene blue (MB) aqueous solution compared with the pristine ZnO NR array. Therefore, our finding indicates that this method may be employed to synthesize porous nanostructures on devices.