ELECTRON-PARAMAGNETIC RESONANCE AND ELECTRON-SPIN ECHO MODULATION ANALYSIS OF THE SILVER ATOM ENVIRONMENT IN GAMMA-IRRADIATED SILVER-EXCHANGED SODIUM MONTMORILLONITE AND ITS AL-13 PILLARED DERIVATIVE

Silver atoms are formed by radiolytic reduction at 77 K of Ag+-exchanged montomorillonite and Al13 pillared montmorillonite clays. EPR shows that the Ag-atom hyperfine constant is about the same as for Ag(o) generated in glassy aqueous solutions and distinctly different from Ag(o) generated in polycrystalline aqueous solutions. This indicates that the water environment in the clay interlayer region is rather disordered as in a glassy matrix. Electron spin echo modulation analysis shows that Ag(o) in the fully hydrated clay is coordinated by four water molecules in its first solvation shell as in bulk solution and that this number decreases as the montmorillonite is dehydrated. For solvation of Ag(o) by methanol and ethanol, however, the Ag(o) is solvated by fewer alcohol molecules in the clay interlayer than in bulk solution. No Al-27 modulation is observed for Ag(o) in montmorillonite even when partially dehydrated, indicating that Ag(o) does not interact with Al-27 in the octahedral sheet of a clay layer. However, Al-27 modulation is detected in Al13 pillared montmorillonite, showing Ag(o) interaction with Al-27 in the pillar. No paramagnetic Ag clusters are observed in the clays in contrast to their ready formation in zeolites and in frozen solutions.