Effect of V-UV-radiation on VOCs-saturated zeolites

Abstract

The combination of adsorption on zeolites and vacuum ultraviolet (V-UV) irradiation was applied to the treatment of gaseous effluents containing volatile organic compounds (VOCs). A xenon-excimer (Xe 2*) radiation source emitting at 172 nm was employed and two types of zeolites (faujasite Y (DAY) and ZMS-5 (DAZ)) were tested in adsorption/irradiation cycles of three model VOC pollutants (1-butanol, benzene and toluene). A specific diffusion cell was used in dynamic experiments for producing air streams containing each VOC at chosen and stable concentrations. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) analyses were performed on the solids after VOC saturation and irradiation. Important changes were detected in the properties of the DAY zeolite when using toluene as a pollutant. In particular, the Si/Al ratio was modified at the surface and in the framework of the zeolite, as a consequence of a rearrangement of the Al and Si atoms in the solid. In contrast, the DAZ zeolite retained its superficial and structural properties after V-UV treatment. In the case of 1-butanol, changes in the zeolite structure were negligible, and no change was observed in the zeolite in the case of benzene. Solid state NMR analysis confirmed these results and revealed that when the DAY zeolite saturated with toluene was irradiated at 172 nm, changes in the shifts of Si and Al atoms took place, suggesting a possible interaction/reaction between the zeolite framework and the benzyl radical produced as a consequence of the toluene oxidation.