Electric field driven fast fabrication of 3D ordered Nano-micro hierarchical ammonium oxofluorotitanates towards mesocrystalline anatase TiO2

Hui Li; Zixue Su

doi:10.1016/j.jcis.2022.03.016

Electric field driven fast fabrication of 3D ordered Nano-micro hierarchical ammonium oxofluorotitanates towards mesocrystalline anatase TiO₂

J Colloid Interface Sci. 2022 Jul:617:267-273. doi: 10.1016/j.jcis.2022.03.016. Epub 2022 Mar 7.

Authors

Hui Li¹, Zixue Su²

Affiliations

¹ School of Environment and Energy, South China University of Technology, Guangzhou 510006, China. Electronic address: lih_37@163.com.
² School of Environment and Energy, South China University of Technology, Guangzhou 510006, China; Guangdong Provincial Key Laboratory of Atmospheric Environment and Pollution Control, Guangzhou 510006, China; Guangdong Provincial Key Laboratory of Solid Wastes Pollution Control and Recycling, Guangzhou, Guangdong 510006, China. Electronic address: zixuesu@scut.edu.cn.

PMID: 35278864
DOI: 10.1016/j.jcis.2022.03.016

Abstract

In this work, 3D ordered nano-micro hierarchical ammonium oxofluorotitanates are synthesized by in-situ dissolution of anodically grown TiO₂ nanotubes and subsequent hydrolysis of (NH₄)₂TiF₆ in an electrochemical cell via a nonclassical crystallization process by external electric field driven oriented particle attachment. The obtained ammonium oxofluorotitanate products are of mesocrystalline structure consisting of nanocrystalline building units oriented aligned at atomic level. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) characterizations are applied to reveal the morphology, structure and crystal phase of grown samples. By controlling the current density or/and content of ammonium fluoride, it is able to grow well-defined (NH₄)₃TiOF₅ octahedrons and truncated octahedrons, (NH₄)₂TiOF₄ nanorods and NH₄TiOF₃ disks. The transformation from (NH₄)₃TiOF₅ octahedrons to truncated octahedrons is ascribed to the different ratios of growth rate for {111} planes and {100} planes. While the decrease of concentration of ammonium fluoride accounts for the crystal phase changes from (NH₄)₃TiOF₅ to (NH₄)₂TiOF₄ and finally to NH₄TiOF₃ disks. Upon thermal annealing, all these ammonium oxofluorotitanates could be converted to mesoporous hierarchical anatase TiO₂ retaining their exterior morphology and keeping the orientation ordering of subunit nanoparticles, which could exhibit excellent photocatalytic activity when acting as photocatalyst in the photo-degradation of methylene blue.

Keywords: Ammonium oxofluorotitanate; External electric field; Mesocrystal; Morphology control; Non-classical crystal growth; Oriented particle attachment; TiO(2).