Interactions of 4-Chlorophenol with TiO2 Polycrystalline Surfaces: A Study of Environmental Interfaces by NEXAFS, XPS, and UPS

ALEXANDER ORLOV; DAVID J. WATSON; FEDERICO J. WILLIAMS; MINTCHO TIKHOV; RICHARD M. LAMBERT

LANGMUIR

AMER CHEMICAL SOC

Año: 2007 vol. 23 p. 9551 - 9554

0743-7463

Despite a significant body of literature on the photocatalytic decomposition of 4-chlorophenol by TiO2 at liquid/solid and gas/solid interfaces, a fundamental understanding of the interaction of 4-chlorophenol with TiO2 is lacking. We present the first study of this interaction under well-defined UHV conditions by means of NEXAFS, time-dependent XPS, and UPS. XPS data show that the molecule adsorbs with the carbon framework intact and no scission of the C-Cl bond. The NEXAFS results indicate a coverage-dependent tilted geometry for the adsorbed molecule that is attached to the surface via a phenolate link. In contrast, because of the absence of an OH functionality, 1,2,4- trichlorobenzene lies flat. The adsorption of 4-chlorophenol is accompanied by a decrease in the TiO2 work function pointing to adsorbate f substrate charge transfer. Interestingly, the UPS data suggest that 4-chlorophenol adsorption leads to the photosensitization of TiO2, thus providing a basis for understanding recent results on the visible light photocatalytic activity of TiO2 for 4-chlorophenol decomposition. It is also found that the molecule is stable against thermal decomposition at temperatures of up to ∼473 K, which is well above the temperature range used for photocatalytic decomposition studies.