Effect of annealing temperature on morphology, structure and photocatalytic behavior of nanotubed H2Ti2O4(OH)2

TL;DR

This study investigates how annealing temperature affects the morphology, structure, and photocatalytic activity of nanotubed H2Ti2O4(OH)2, revealing thermal instability and changes in photocatalytic efficiency related to dehydration and defect formation.

Contribution

It provides new insights into the thermal behavior and photocatalytic properties of nanotubed H2Ti2O4(OH)2, highlighting the effects of annealing on its structure and performance.

Findings

Nanotubed H2Ti2O4(OH)2 is thermally unstable.

Dehydration occurs in two steps involving SETOV formation.

Higher annealing temperatures reduce photocatalytic activity due to defect interactions.

Abstract

Nanotubed titanic acid (H2Ti2O4(OH)2) was prepared from nanotubed sodium titanate (Na2Ti2O4(OH)2) by an ion exchange reaction in a pH=1 HCl solution. The effect of annealing temperature on the morphology, structure and photocatalytic behavior of nanotubed H2Ti2O4(OH)2 was studied by means of TEM, XRD, DTG, DSC, BET and ESR. The results showed that nanotubed H2Ti2O4(OH)2 is thermally unstable. Its dehydration consists of two steps. In the first-step dehydration, single-electron-trapped oxygen vacancies (SETOVs) were generated. Accompanying the second-step dehydration, the transition of crystal form from orthorhombic system to anatase took place, at the same time the nanotubes broke. At T>300 {\deg}C, when the SETOV concentration greatly increased, the interaction between SETOV happened. (VOo)x formed could play the role of recombination center of photogenerated e--h+ and make the photocatalytic behavior of TiO2 (anatase, obtained from 500 {\deg}C-treated nanotubed H2Ti2O4(OH)2) to become bad.