Synthesis of Pure Brookite Nanorods in a Nonaqueous Growth Environment

Mahmoud Hezam,Saif M H Qaid,Mohammad Khaja Nazeeruddin,Fahhad Alharbi,Idriss M Bedja,Abdullah Aldwayyan

doi:10.3390/cryst9110562

Abstract

Brookite TiO2 is the most difficult TiO2 polymorph to synthesize. The available methods in the literature to produce brookite nanostructures mostly use water-based techniques for the preparation of water-soluble Ti complexes first, followed by a hydrothermal growth of the brookite nanostructures. Besides its multi-step nature, achieving a single brookite phase and optimizing the aqueous growth environment are all issues to be hardly controlled. In this work, pure brookite TiO2 nanorods are synthesized using tetrabutyl titanate Ti(OBu)4 and Sodium Fluoride (NaF) as precursor materials in a simple non-aqueous one-pot solvothermal process. Alcoholysis of only Ti(OBu)4 in ethanol resulted in pure anatase nanoparticles, while the addition of NaF was essential to promote the growth of highly pure brookite nanorods. The phase purity is confirmed by X-Ray Diffraction, Raman Spectroscopy, and High-Resolution Transmission Electron Microscopy. The growth mechanism is explained according to the Ostwald’s step rule, where Na+ ions are anticipated to have a potential role in driving the growth process towards the brookite phase.

Highlights

Titanium dioxide (TiO2 ) is a far-reaching multi-functional industrial material that has been in wide use for many significant applications such as photocatalysis, solar cells, cosmetics, pigments and protective coatings [1,2,3,4,5,6,7,8]
The sample prepared with NaF could be fully indexed as pure brookite, while the non-NaF sample has a pure anatase phase
Na+ ions are obviously unique in driving the crystallization process into the brookite phase pathway rather than anatase or rutile, a fact that is shown by our results and that has been found to hold, as mentioned above, in water-based environments as well

Summary

Introduction

Titanium dioxide (TiO2 ) is a far-reaching multi-functional industrial material that has been in wide use for many significant applications such as photocatalysis, solar cells, cosmetics, pigments and protective coatings [1,2,3,4,5,6,7,8]. Water-soluble complexes are usually used as titanium precursors, and the effect of growth parameters such as pH, temperature and complex ligands have been well addressed in the literature [12,18,20]. It has been observed by many authors that the brookite phase is promoted under highly basic conditions [12,13]. Buonsanti et al reported a sophisticated surfactant-assisted nonaqueous method for the growth of pure brookite nanocrystals using high-temperature aminolysis of titanium carboxylate complexes [15]. Our method is based on the direct alcoholysis of Ti(OBu) in ethanol in the presence of sodium fluoride (NaF) salt

Materials and Methods

Results and Discussion

Conclusions