DIELECTRIC-PROPERTIES AND DYNAMIC SIMULATION OF WATER BOUND TO TITANIA SILICA SURFACES

Water adsorbed on titania/silica (TS) surfaces has been studied by dielectric spectroscopy (DS) in the 3-10 MHz frequency range at T = 120-300 K, thermally stimulated depolarization (TSD) at the same temperatures, H-1 NMR, and quantum chemical methods. The TSD spectra of TS have only one relaxation maximum after sample heating at 400 K. The activation energies of depolarization (TSD) and polarization (DS) decrease at TiO2 content increasing in TS. According to the TSD, DS, and H-1 NMR data, water adsorbed on the TS surfaces essentially in the interface-region forms more weakly bound clusters than on the silica surfaces. Simulation of vibrational-rotational relaxation of the water molecules attached to the TS surfaces shows that the activation energy of rotation is a maximum for the molecules having donor-acceptor bonds, Me<--OH2 (Me = Si, Ti), in the complexes HO-Me<--OH2 + mH(2)O and it is minimum for one water molecule linked to the Ti-O(H)-Si bridge through a hydrogen bond.