Structural role of polyethylene glycol in the formation of anatase nanocrystalline titania at low temperature

Abstract

AbstractAnatase nanocrystalline TiO2 thin films were obtained by a sol–gel dip‐coating method, in which the nanocrystallization is effected by a simple hot water treatment of the deposited films at temperatures below 90 °C under atmospheric pressure for 1 h. The dip‐coating sol was prepared by reacting titanium tetra‐n‐butoxide [Ti(OnBu)4] with polyethylene glycol (PEG) in ethanol. Films obtained from a sol that do not contain PEG show no sign of crystallization, demonstrating the importance of PEG in the crystallization process. Raman studies of reaction dynamics show that PEG undergoes a nucleophilic substitution reaction replacing butoxy groups in Ti(OnBu)4. Stoichiometric reactions of Ti(OnBu)4 with PEG in polar and nonpolar solvents were performed, and they yielded different titanium–PEG hybrid polymers, which were isolated and characterized by various spectroscopic techniques such as IR, Raman, solid‐state NMR and MALDI‐TOF‐MS. NMR studies evidenced the location and the way in which PEG is bonded with titanium atoms in the titanium–PEG hybrid polymers. On the basis of these studies, we have proposed structures for these polymers. It is demonstrated that the structure of the obtained polymers plays an important role in the formation of anatase TiO2 nanoparticles in hot water at temperatures below 90 °C under atmospheric pressure. Copyright © 2009 John Wiley & Sons, Ltd.