Dehydration-rehydration processes in zeolites A: crystal-chemical characterization and possible application to improve the selectivity of gas sensors

The efficiency of hydrophilic zeolite A in its Na-, Na,K- and Na,Ca-form (4A, 3A and 5A, respectively) as an absorbing water molecules filter was tested after repeated thermal rigeneration cycles. The zeolite samples were characterized by means of thermogravimetric (TG) and X-ray diffraction (XRD) analyses. Water absorption capacity for all samples remains approximately the same after repeated dehydration-rehydration cycles and even if the process is accelerated. Rietveld structure refinements revealed no significant structural changes as a function of the number of regeneration cycles; slight variations of framework T-O distances and T-O-T angle were only recorded after the thermal activation