Hierarchical zeolites as adsorbents for mesosulfuron-methyl removal in aqueous phase

Bulky organic pollutants such as pesticides and pharmaceutical residues are found in wastewater and are difficult to remove by microporous adsorbents because of their large size. Hierarchical zeolites as potential adsorbents for removal of heavy organic pollutants from aqueous phase are investigated. Hierarchical HMOR and HZSM-5 samples were obtained by post-synthesis desilication by alkaline treatment followed or not by acid leaching of the microporous parent zeolites. The obtained materials have been fully characterized by X-ray diffraction, N2 physisorption, elemental analysis, pyridine adsorption followed by FTIR. Alkaline treatments lead to a framework desilication creating mesopores with the preservation of the Brønsted acidity. Material adsorption behaviors are studied in pesticide, mesosulfuron-methyl (MM), removal from aqueous phase. For all the materials, adsorption kinetics are well described by a pseudo-second order model indicating that MM molecules are chemisorbed via acido-basic interaction of the neutral form. Sorption isotherms are S-shape isotherms for the parent samples and evolve to more favorable concave isotherms for highly mesoporous samples. Thus hierarchical zeolites exhibit higher sorption rate and capacities than microporous ones. Soft acid leaching treatments carried out after alkaline one help to clean the zeolite porosity from silica debris and to enhance significantly zeolite adsorption efficiency.