Water contaminants adsorption onto micro and mesoporous materials

Many environmental pollutants of emerging concern can escape from remediation in conventional wastewater treatment plants, hence they could be found in surface waters at low concentration levels. The removal of these contaminants requires new technological solutions, an application field where siliceous porous materials seem to be particularly useful thanks to their adsorption properties. In fact, zeolites have been used as adsorbent media for specific classes of chemicals, including hydrocarbons, halocarbons and pharmaceuticals [1,2]. Moreover, due to their high chemical and thermal stabilities, these materials can be considered environmentally compatible. This study has a dual purpose: 1) to measure the sorption capacity of organophilic zeolites (BEA, Y and ZSM-5) and a mesoporous silica material (MCM-41) towards various organic compounds in water, in order to verify their removal efficiency for potential use in wastewater and groundwater remediation and 2) to understand the structure features for adsorption of organic contaminants in aqueous solutions. The adsorption process was very fast in all zeolites towards several classes of pollutants. Adsorption isotherms and thermogravimetric analysis revealed that the amount of the organic pollutant embedded inside the framework is related both to lattice structure and to adsorbent hydrophobicity. The adsorption capacity of a given materials depends also on the pH of the solution and on the ionization constant of the target molecule. The competitive adsorption of two components (i.e. dichloroethane and methylterbutylether / ZSM-5) was proved also by X-ray analysis: diffractometric data showed that methylterbutylether was preferentially adsorbed into the straight 10-ring channel of the ZSM-5 whereas dichloroethane molecules were preferably hosted in the sinusoidal channel. The process of competitive adsorption for a binary mixture of contaminants occurs with a reorientation of the adsorbed species. Another field where the study of the adsorption of pharmaceuticals by siliceous porous materials could be of great interest is the drug delivery in nanomedicine applications. These materials could be employed for hosting and in-situ delivering a variety of molecules of pharmaceutical interest, which are selectively entrapped within their pores and specifically transported in the body to an exact location.