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

Abstract

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.