Pentylcyanobiphenyl as Test Molecule for the Acid Sites of Powdered Titanium(IV) Oxides: Sensitivity of Core Levels to the Local Structure

Abstract

Pentylcyanobiphenyl was used successfully as a test molecule to show the acid sites upon some commercial nanoscaled titanium dioxide materials. The surface interactions were investigated in detail using methods sensitive to the surface or to the bulk material, e.g., X-ray photoelectron spectroscopy (XPS), infrared spectroscopy, and thermal analysis. Different oxidation states of surface Ti ions were revealed. Several species were found: the majority were bonded through the nitrogen lone pair of the cyano group, but bonding to the surface OH groups by benzene π electrons might also appear. The N 1s lines of adsorbed 5CB were able to distinguish between Lewis acid and relatively weak Brønsted acid sites.

Keywords:

• Infrared spectra
• pentylcyanobiphenyl
• size dependence
• titanium dioxide
• XPS

Acknowledgments

The authors thank the Romanian Ministry of Education and Research for financial support by the Project COMAFI of the CORE Program. Valuable discussions with M. F. Lazarescu (NIMP) and the BET measurements performed by B. Cojocaru (Bucharest University) are highly appreciated.