SURFACE-CHEMISTRY OF PERFLUORO ETHERS - AN INFRARED STUDY OF THE THERMAL-DECOMPOSITION OF (C2F5)(2)O ON AL2O(3)

The adsorption and thermal decomposition of a model polyperfluorinated ether on high surface area Al2O3 has been studied using transmission infrared spectroscopy. It has been found that (C2F5)(2)O interacts with the isolated OH groups on the Al2O3 surface, forming an increasing number of associated OH groups from 150 to 600 K. Surface fluoroacetate and surface fluoroformate species are also formed from the thermal decomposition of the (C2F5)(2)O layer. At temperatures higher than 300 K, the surface fluoroacetate converts to surface fluoroformate. Oxidation of the (C2F5)(2)O molecules also occurs on a surface preadsorbed with pyridine, indicating that Lewis acid Al3+ sites, blocked by pyridine adsorption, are not involved in fluoroacetate and fluoroformate production. The absence of a chemical reaction between the (C2F5)(2)O adlayer and a (CH3)(3)SiCl-treated Al2O3 surface indicates that the presence of available surface hydroxyl groups is necessary for the oxidation of the perfluoro ether by Al2O3. A mechanism for the thermal decomposition of(C2F5)(2)O on Al2O3 is proposed.