Effect of pH on the Formation of Amorphous TiO2 Complexes and TiO2 Anatase during the Pyrolysis of an Aqueous TiCl4 Solution

Huyen Duong Ngoc,Dung Mai Xuan,Tuan Mai Van

doi:10.3390/catal10101187

Abstract

The titanium dioxide (TiO2) nanostructures resulted by the pyrolysis of titanium tetrachloride (TiCl4) at a low temperature of 80 °C were found to be a mixture of amorphous TiO2 complexes and anatase nanostructures, whose ratio depends on the pH of the pyrolysis medium. At a low pH level, the resulting TiO2 nanostructures are predominantly anatase and gradually shift to amorphous TiO2 complexes as the pH level increases. Moreover, the amorphous TiO2 complexes can convert back to anatase nanostructures by a post-heating treatment, and can then transform to rutile with elevating temperature. Amongst the TiO2 nanostructures recovered from the amorphous TiO2 complexes, anatase appears to be the most effective photocatalyst in the decomposition of methylene blue.

Highlights

Titanium dioxide (TiO2 ), a typical metal oxide with a high refractive index, chemical stability, long durability, and nontoxicity, has been widely used for many applications, such as white pigments, textiles, papers, cosmetics, medicines, and ceramics
The pyrolysis of an aqueous TiCl4 solution generally results in a mixture of anatase nanostructures and amorphous TiO2 complexes
The ratio of TiO2 anatase nanostructures to amorphous TiO2 complexes can be controlled by changing the pH of the pyrolysis medium

Summary

Introduction

Titanium dioxide (TiO2 ), a typical metal oxide with a high refractive index, chemical stability, long durability, and nontoxicity, has been widely used for many applications, such as white pigments, textiles, papers, cosmetics, medicines, and ceramics. From the viewpoint of chemical thermodynamics, before decomposing into TiO2 either in the form of anatase, brookite, or rutile, the titanium precursor undergoes a series of amorphous TiO2 complexes (or intermediates) such as Tix Oy Clz (OH)w , resulting from the pyrolysis of. The pH levels evolving to correlations between H, Cl, and OH radicals in the reaction media were assumed to be the crucial factors to modify and control the resulting TiO2 nanostructures Based on these considerations, in this study, an experiment was carried out to further investigate the effect of an elevated pH level (or OH radical) of the reaction media on the formation of amorphous TiO2 complexes, as well as of the final anatase nanostructures obtained from the pyrolysis of an aqueous TiCl4 solution

Results and Discussion

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Methods

Conclusions