EPR study of the adsorption of dioxin vapours onto microporous carbons and mesoporous silica

Abstract

Computer aided analysis of electron paramagnetic resonance (EPR) spectra of tetrachloro-dibenzodioxin labelled with a nitroxide radical (TCDD-T) was employed to investigate the adsorption of dioxin vapours onto two carbons, the activated carbon (AC) NORIT GL50 and a carbon directly taken from a waste incinerator (WI) plant, termed EVN.2, and a low-polar micelle-templated mesoporous silica, termed lpMTS. Several experimental conditions were varied to optimize the adsorption process and to mimic dioxin adsorption occurring in a WI plant. Solvent vapours did not perturb dioxin adsorption. EPR analysis suggested that the nitroxide labelled-dioxin interacted (dipole–dipole interactions) with oxygenated groups, mainly C–O–C groups of the carbon and siloxane groups of lpMTS. The kinetics of adsorption was analyzed at different flow rates. The adsorption was large for NORIT and lpMTS already after few seconds, but a complete adsorption was achieved with a slow kinetics, whereas the EVN.2 sample showed a negligible adsorption even after 1 min. The results are interpreted in terms of the surface characterization ( S BET, pore volume and pore size distribution) of the adsorbents. The EPR method described in this study can provide useful and unique information on the adsorption process of dioxins onto microporous carbons and mesoporous MTSs. Moreover, this method may be applied to different adsorbates and porous adsorbents.