POSITRON-ANNIHILATION SPECTROSCOPIC INVESTIGATION OF AL-PILLARED MONTMORILLONITES

We report, for the first time, our result on characterisation of Al-pi llared clay using positron annihilation spectroscopy (PAS) along with XRD and BET techniques. Positron life-time spectra for Al-pillared mon tmorillonite, as received and calcined at different temperature (100-5 00 degrees C), along with the parent natural clay are measured. The an nihilation rate of ortho-positronium (o-Ps) increases monotonically wi th calcination temperature up to 300 degrees C and falls subsequently. Similar behaviour is seen for the fraction of o-Ps formed. We interpr et the initial rise in annihilation rate of o-Ps to be due to the incr ease in Bronsted acidity with dehydroxylation of pillars. The reductio n in annihilation rate on calcination at higher temperatures could be due to loss of acidity and/or due to mesopore formation following dela mination of clay structure.