Synthesis and Characterization of Anatase TiO2 Nanorods: Insights from Nanorods’ Formation and Self-Assembly

Seyed Naveed Hosseini,Xiaodan Chen,Arnout Imhof,Alfons Van Blaaderen,Patrick J Baesjou

doi:10.3390/app12031614

Seyed Naveed Hosseini, Xiaodan Chen + Show 3 more

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https://doi.org/10.3390/app12031614

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Journal: Applied Sciences	Publication Date: Feb 3, 2022
Citations: 6	License type: CC BY 4.0

Affiliation: Utrecht University

Abstract

Highly crystalline, organic-solvent-dispersible titanium dioxide (TiO2) nanorods (NRs) present promising chemicophysical properties in many diverse applications. In this paper, based on a modified procedure from literature, TiO2 NRs were synthesized via a ligand-assisted nonhydrolytic sol-gel route using oleic acid as the solvent, reagent, and ligand and titanium (IV) isopropoxide as the titanium precursor. This procedure produced monodisperse TiO2 NRs, as well as some semi-spherical titania nanocrystals (NCs) that could be removed by size-selective precipitation. X-ray diffraction and selected area electron diffraction results showed that the nanorods were anatase, while the semipheres also contained the TiO2(B) phase. By taking samples during the particle growth, it was found that the average length of the initially grown NRs decreased during the synthesis. Possible reasons for this unusual growth path, partially based on high-resolution transmission electron microscopy (HRTEM) observations during the growth, were discussed. The dispersion of anatase TiO2 nanorods was capable of spontaneous formation of lyotropic liquid crystals on the TEM grid and in bulk. Considering high colloidal stability together with the large optical birefringence displayed by these high refractive index liquid crystalline domains, we believe these TiO2 NRs dispersions are promising candidates for application in transparent and switchable optics.

Highlights

Nanocrystalline TiO2 has been receiving increasing attention in many applications such as optoelectronics [1], catalysis and photocatalysis [2,3,4,5,6,7,8], solar energy conversion [9], gas sensing [10], and nanostructured coatings for biomedical implants due to its modified material properties and chemical reactivity at the nanoscale [11]
To effectively separate TiO2 NRs in terms of their length with the desired polydispersity index, a size-selective precipitation process was performed on as-synthesized TiO2 NCs
We found that to achieve a higher yield of monodisperse NRs, it was crucial to separate first the larger NCs from the reaction mixture just through centrifugation prior to the addition of antisolvent in the size-selective precipitation process

Summary

Introduction

Nanocrystalline TiO2 has been receiving increasing attention in many applications such as optoelectronics [1], catalysis and photocatalysis (such as water splitting, air, and water purification) [2,3,4,5,6,7,8], solar energy conversion [9], gas sensing [10], and nanostructured coatings for biomedical implants due to its modified material properties and chemical reactivity at the nanoscale [11]. Anatase and the less common brookite and titanium dioxide bronze phase (TiO2 (B)), are formed commonly at the nanoscale [14,15]. The transformation sequence among anatase, brookite, and rutile is size-dependent and their transformation into each other can be reversed even by slight differences in the surface energies [8]. In the case of TiO2 (B), it can be nucleated directly from the solution as a metastable phase and tends to transform into anatase titania at temperatures above 800◦ K [17]

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