Direct growth of ZnO nanorods on biogenic hierarchical rice husk SiO₂ and their application to dye degradation

ZnO nanorods/hierarchical SiO₂ porous composites are successfully obtained from biogenic-template method with ZnCl₂ and rice husks as raw material by a simple double-step annealing process. The structure and optical properties were characterized by XRD, SEM, TEM, XPS and UV–Vis spectra to understand the growth mechanism of ZnO nanorods on biogenic hierarchical SiO₂. Vertically aligned with high regularity and density ZnO nanorods were developed on porous SiO₂ when the treated temperature was 600 °C under N₂ gas and post-treating in muffle furnace at 450 °C in the air. The results showed that ZnCl₂ played an important role in acting as the zinc source and morphology director during the formation of ZnO nanostructures. At initial stage, ZnCl₂ melted from the raw material and diffused onto the rice husk surface to formed flake structure ZnOCl₂·H₂O when the treated temperature was lower than 500 °C under N₂ gas. The former was responsible for proto-nanorods (template) formation of ZnO nanorods. The as-prepared samples displayed high photocatalytic activity for the degradation of rhodamine B under ultraviolet (UV) irradiation.