Evolution of Hollow TiO2 Nanostructures via the Kirkendall Effect Driven by Cation Exchange with Enhanced Photoelectrochemical Performance

• Published in: Nano letters Vol. 14; no. 5; pp. 2528 - 2535
• Main Authors: Yu, Yanhao, Yin, Xin, Kvit, Alexander, Wang, Xudong
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 14-05-2014
• Subjects: Catalytic methods; Chemical synthesis methods; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Diffusion in nanoscale solids; Diffusion in solids; Exact sciences and technology; Low-dimensional structures (superlattices, quantum well structures, multilayers): structure, and nonelectronic properties; Materials science; Methods of nanofabrication; Physics; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Transport properties of condensed matter (nonelectronic); vapor−solid deposition; Kirkendall effect; Hollow TiO2 nanostructure; photoelectrochemical water splitting; cation exchange; DNA replication; Catalysts; Nanotubes; Template reaction; Crystal growth from vapors; Nanostructures; Vapor deposition; Vapor phase; Morphology; Growth mechanism; Illumination; Surface area; Diffusion; Ion exchange; Nanostructured materials; Nanomaterial synthesis
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/nl5002907

Hollow nanostructures are promising building blocks for electrode scaffolds and catalyst carriers in energy-related systems. In this paper, we report a discovery of hollow TiO2 nanostructure evolution in a vapor–solid deposition system. By introducing TiCl4 vapor pulses to ZnO nanowire templates, we obtained TiO2 tubular nanostructures with well-preserved dimensions and morphology. This process involved the cation exchange reaction between TiCl4 vapor and ZnO solid and the diffusion of reactants and products in their vapor or solid phases, which was likely a manifestation of the Kirkendall effect. The characteristic morphologies and the evolution phenomena of the hollow nanostructures from this vapor–solid system were in a good agreement with the Kirkendall effect discovered in solution systems. Complex hollow TiO2 nanostructures were successfully acquired by replicating various ZnO nanomorphologies, suggesting that this unique cation exchange process could also be a versatile tool for nanostructure replication in vapor–solid growth systems. The evolution of TiO2 nanotubes from ZnO NW scaffolds was seamlessly integrated with TiO2 NR branch growth and thus realized a pure TiO2-phased 3D NW architecture. Because of the significantly enlarged surface area and the trace amount of Zn left in the TiO2 crystals, such 3D TiO2 nanoforests demonstrated enhanced photoelectrochemical performance particularly under AM (air mass) 1.5G illumination, offering a new route for hierarchical functional nanomaterial assembly and application.