Hierarchical nanostructures of K-birnessite nanoplates on anatase nanofibers and their application for decoloration of dye solution

This paper reports a simple method for fabricating hierarchical nanostructures consisting of K-birnessite (K_xMnO₂) nanoplates on anatase (TiO₂) nanofibers. The nanofibers were prepared in the form of a composite by electrospinning, followed by calcination at 500°C in air for 2 h. The nanofibers were then immersed in a sulfuric acid solution containing KMnO₄ at 90°C for 20 min to deposit the K_xMnO₂ nanoplates. The nanoplates had a thickness of ∼5 nm and an edge length of ∼150 nm, and were oriented perpendicular to the nanofibers. They were confirmed as K-birnessite by XRD and EDX measurements. The density of the K_xMnO₂ nanoplates could be controlled by simply adjusting the concentration of KMnO₄ and/or the deposition time. We also investigated the growth mechanism in light of surface roughness for the nanofibers and spatial confinement for the plates. We further demonstrated the potential use of these hierarchical nanostructures for waste water treatment by removing congo red from an aqueous solution. They exhibited good performance in both batch and continuous flow studies.