ESR characterization of vanadium centers supported on Al-containing mesoporous silica

The properties of Al-substituted mesoporous silicas modified with VO2+, ion s in a one-step exchange reaction in aqueous medium have been investigated by means of ESR. The vanadium centers exist at the surface in a well disper sed form. ESR identifies two types of vanadyl ions: (a) fully hydrated VO2 ions, retaining motional freedom at room temperature, and (b) species firm ly bound to the surface due to the formation of inner-sphere complexes. The contribution of the latter increases with Al substitution. The phenomenon is discussed in terms of a gradual modification of the surface properties a s a result of Al incorporation. (C) 2001 Elsevier Science B.V. All rights r eserved.