Domestic wastewaters contain a variety of organic wastewater contaminants such as pharmaceuticals and personal care products. It has been proven that most of these compounds undergo both incomplete removal in wastewater treatment plants and slow natural degradation, consequently they are found in surface waters receiving effluent from treatment plants. In Italy, it was found that the most abundant residual drugs in surface waters were antibiotics. This class of pharmaceuticals are of particular concern because their presence in natural waters contributes to the spread of antibiotic resistance in microorganisms. The aim of this work is to investigate the capability of hydrophobic commercial zeolites (Mordenite, Y, ZSM-5, Beta) in removing two test antibiotics Levofloxacin (FLX) and Erythromycin (ERY). The selected zeolites differ in topology, channel systems, free window apertures, hydrophobicity (SAR: Silica/Alumina Ratio) and thermal treatment (calcination). The employment of zeolites as adsorbent materials has a dual potential use: 1) improve the wastewater and groundwater efficiency remediation and 2) test these siliceous porous materials in nanomedicine applications, like drug delivery systems (i.e. devices that enable for an accurate control the rate at which drug molecules are delivered into the bloodstream). ERY adsorption was studied only on Y, MOR and Beta zeolites since its molecular dimensions are too large when compared to the ZSM-5 cage. From Fig. 1a it can be seen that ERY adsorption on calcined Beta decreases with the hydrophobicity of the material, showing that drugs adsorption depends on both ionic and hydrophobic interactions. Fig. 1b shows that FLX adsorption on Y is higher than that on MOR: this difference cannot be related solely to the molecular dimension, since the access window cross section in Y and MOR are comparable, hence they could be due to the dispersive interaction between the adsorbate and the zeolite pore walls. Finally, chromatographic, structural and thermogravimetric measurements demonstrate that the selected zeolites show fast adsorption kinetics and good removal properties for the studied antibiotics from water.
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