Dynamic Diffraction Studies on the Crystallization, Phase Transformation, and Activation Energies in Anodized Titania Nanotubes.

Hani Albetran,Victor Vega,Victor Prida,It-Meng Low

doi:10.3390/nano8020122

Abstract

The influence of calcination time on the phase transformation and crystallization kinetics of anodized titania nanotube arrays was studied using in-situ isothermal and non-isothermal synchrotron radiation diffraction from room temperature to 900 °C. Anatase first crystallized at 400 °C, while rutile crystallized at 550 °C. Isothermal heating of the anodized titania nanotubes by an increase in the calcination time at 400, 450, 500, 550, 600, and 650 °C resulted in a slight reduction in anatase abundance, but an increase in the abundance of rutile because of an anatase-to-rutile transformation. The Avrami equation was used to model the titania crystallization mechanism and the Arrhenius equation was used to estimate the activation energies of the titania phase transformation. Activation energies of 22 (10) kJ/mol for the titanium-to-anatase transformation, and 207 (17) kJ/mol for the anatase-to-rutile transformation were estimated.

Highlights

Titania is a promising and attractive raw material for its use in various applications such as hydrogen production, gas sensors, photoelectrochemical cells, and dye-sensitized solar cells because of its stability, nontoxicity, photo-durability, affordability, and excellent photocatalytic activity [1,2,3,4,5].Anatase, rutile, and brookite are three common naturally occurring titania crystal structures [6,7,8,9]
Isothermal heating of the anodized titania nanotubes by an increase in the calcination time at 400, 450, 500, 550, 600, and 650 ◦C resulted in a slight reduction in anatase abundance, but an increase in the abundance of rutile because of an anatase-to-rutile transformation
The effect of calcination time on the titania phase transformation has not been investigated intensively and is not yet clear and fully understood. Some studies of this effect exist in the literature, for example, titanium dioxide nanotube arrays have been heated at 500 ◦C/min and 10 ◦C/min with a calcination time of 1, 2, 4, 8, and 12 h [18]

Summary

Introduction

Titania is a promising and attractive raw material for its use in various applications such as hydrogen production, gas sensors, photoelectrochemical cells, and dye-sensitized solar cells because of its stability, nontoxicity, photo-durability, affordability, and excellent photocatalytic activity [1,2,3,4,5]. The effect of calcination time on the titania phase transformation has not been investigated intensively and is not yet clear and fully understood Some studies of this effect exist in the literature, for example, titanium dioxide nanotube arrays have been heated at 500 ◦C/min and 10 ◦C/min with a calcination time of 1, 2, 4, 8, and 12 h [18]. The crystalline phase transformation process of amorphous-to-anatase in the titania nanotubes arrays can be observed by using a hydrothermal treatment method under various reaction times, and at low temperature experimental conditions (~180 ◦C) [26,29]. The effect of calcination time on phase transformations, crystallization kinetics, and activation energies of anodized titania nanotube arrays was investigated using isothermal in-situ synchrotron radiation diffraction (SRD) from room temperature to 900 ◦C. The sample was characterized using field emission scanning electron microscopy (FESEM), and associated energy dispersive spectroscopy (EDS)

Sample Preparation

Field Emission Scanning Electron Microscopy

Quantitative Analysis

Crystallization Activation Energies

Conclusions