Analysis of Water-Assisted Crystallization Process in Anodically Grown Titania Nanotube Arrays

Sunday, 1 October 2017: 14:10
Maryland 2 (Gaylord National Resort and Convention Center)
I. B. Ahiabu (Universtiy of Houston), M. Paulose, and O. K. Varghese (University of Houston)
Titania nanotube arrays grown using anodic oxidation have exhibited enormous potential as a semiconductor nanoarchitecture beneficial for a wide range of applications including solar energy conversion and storage. High degree of crystallinity is a pre-requisite for several of these applications. While conventional furnace annealing has long been identified as an effective method to crystallize the amorphous as-prepared nanotubes, recent research efforts to reduce the thermal budget revealed that titania nanotube arrays could be crystallized using water at or near room temperature. Crystallization and phase transformation was, however, accompanied by morphological changes. Although several reports on the topic appeared after this finding, most of these papers presented conflicting information on the mechanism of crystallization at room temperature and performance of this material when used for applications such as photocatalysis that exploit semiconducting properties. While some groups believed water as responsible for the crystallization, some others attributed it to electrolyte species such as fluorine. We performed a comprehensive investigation on water-assisted crystallization of nanotubes prepared under different conditions and our study revealed the true process behind crystallization. The quantum efficiency measurements on solar photoelectrochemical fuel generation cells fabricated using the room-temperature water crystallized nanotubes showed almost no improvement in the photocatalytic properties despite having the phase transition from amorphous to anatase. We will discuss the details of our findings in this presentation.