A biomass composite based on natural deep eutectic solvent and magnetic chitosan for the solid phase extraction of PPCPs

Abstract

Water pollution has always been a concern. The synergistic function of deep eutectic solvents (DESs) and adsorbent materials has aroused continuous attention, especially in terms of water pollution. In this study, four natural DESs were synthesized from choline chloride ([ChCl]) with glucose ([Glu]), fructose ([Fru]), sucrose ([Suc]) and maltose ([Mal]), respectively. The DESs were then coated onto the surface of magnetic chitosan (MCS) to form DESs-MCS composites. The structures of the DESs-MCS were confirmed by XRD, FT-IR, VSM, TGA and TEM. Afterwards, the DESs-MCS was combined with solid phase extraction (SPE) to separate PPCPs (production and extensive application of pharmaceuticals and personal care products) including diclofenac sodium salt (DCF) and tetracycline (TC). [ChCl][Fru]-MCS was selected as a representative adsorbent to extract DCF, and some influencing factors such as the mass of the [ChCl][Fru]-MCS, the volume of the DCF solution and the type of the desorption solvent were systematically investigated. Moreover, the adsorption of DCF was well conformed to the Langmuir adsorption isotherm and the Pseudo-Second-Order kinetic model. The maximum adsorption capacity of [ChCl][Fru]-MCS on DCF was up to 180.2 mg∙g−1. Furthermore, the relationship between solution pH and adsorption capacity, combined with XPS and FT-IR analysis of the [ChCl][Fru]-MCS before and after adsorption, were explored to get insight into the adsorption mechanism. It turned out that the electrostatic interactions play a vital role in the extraction process, and the hydrogen bonding was also considered as the main driving force based on the types of the functional groups of DES (such as –OH, –NH2). At last, the practical applicability of the [ChCl][Fru]-MCS was evaluated by performing the regeneration experiments and analyzing the real sample. The results demonstrated that the [ChCl][Fru]-MCS could be recycled six times without significant loss of adsorption capacity and the [ChCl][Fru]-MCS could be successfully applied to extract DCF from environmental water samples. The limit of detection and limit of quantification obtained for DCF were 0.27 and 0.90 μg∙mL−1, respectively. The RSDs of the precision and repeatability experiments were 0.71 % and 0.35 %, respectively. Hence, the prepared DES-MCS proved to be a potential adsorbent in the field of wastewater.