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

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 (SBET, 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.

Proposed adsorption mechanism of TCDD-T into the micro- and meso-porosities of NORIT-AC and low-polar MTS. Adsorption is negligible on EVN.2 carbon surface due to pore closure by graphitic layers.Figure optionsDownload as PowerPoint slideResearch highlights
► Computer aided EPR informs about TCDD-T vapour adsorption on porous solids.
► Adsorption is measured in EPR cavity over N2 flow rate, time, solvent, temperature.
► Quantitative adsorption is achieved for low polar MTS in 1 min at high flow rates.
► 100 mg NORIT-lpMTS adsorb 70–60 μg TCDD-T in 5 s at flow rate of 1400 dm3/h.
► WI-plant EVN.2 poorly adsorbs TCDD-T due to pore size distribution and graphitization.