Formation of WO3nanotube-based bundles directed by NaHSO4 and its application in water treatment

Abstract

Self-assembly can offer a very powerful tool for the design of novel materials and many different templates have been found to direct the formation of microstructures. In this article, we report a simple method for the self-assembly of three-dimensional (3D) WO₃ nanotube bundles. It is demonstrated that not only can NaHSO₄ act as a reactant, but also, more importantly, it played multiple key roles in the self-assembly processes, while NH₄HSO₄ and KHSO₄ have none of these functions at all. As suggested, at first, WO₃ ordered and layered structures can be generated by the hydrothermal reaction of NaHSO₄ with Na₂WO₄ at 180 °C, and then sodium ions (Na⁺) inserted into the layer cause a continual curl of the WO₃ outer-slice by the repel force of static electricity between Na⁺ ions and H⁺ ions on the surface of the WO₃ slice. Herein, Na⁺ ions can dramatically promote the formation of WO₃ single crystal slices, which are precursors of the self-assembly, and SO₄²⁻ ions can bridge the WO₃ slices as well as the nanotubes. In addition, it is found that the WO₃ nanotube bundles still keep their original aggregation after template removal, and the bundle can be disassembled gradually under a long treatment time of aqueous ultrasonication. Furthermore, the application in wastewater treatment of WO₃ nanotube bundles has been investigated.