Adsorption efficiency enhancing of electrospun polycaprolactone nanofibers towards acidic polar drugs through the incorporation of a composite of graphene oxide nanosheets and Al-30 polyoxocations: a comparative study

The main objective of this study focuses on exploration of the feasibility of Al-30 polyoxocations for preparation of a novel sorbent material for a solid-phase extraction (SPE) method by selective adsorption and extraction of a class of compounds considering the type of interactions involved in the adsorption process. Accordingly, first Al-30 polyoxocations were synthesized and their composite was prepared with graphene oxide (GO) nanosheets as a suitable substrate to be introduced as a SPE sorbent material. Then, the prepared composite was incorporated into polycaprolactone (PCL) nanofibers via electrospinning to present an alternative sorbent for SPE-based on a GO/Al-30 nanocomposite (GO/Al-30 NC) creating no need for filtering or centrifuging steps. Intercalation of Al-30 polyoxocations into the GO layers and the incorporation of GO/Al-30 NC into PCL nanofibers was successfully confirmed through FE-SEM, TEM, EDX, XRD, BET, TGA, IR spectroscopy, and zeta potential determination. For investigating the types of probable interactions involved in the adsorption process of different compounds on the proposed sorbents, four statin drugs, cholesterol-lowering agents with various polarity and ionization properties, were selected as model analytes. Factors affecting the extraction efficiency of dispersive SPE and immersed SPE methods using GO/Al-30 NC and GO/Al-30 NC-PCL nanofibers, respectively, were investigated and optimized. Under optimal conditions, acceptable analytical figures of merit were obtained for both SPE methods. A comparison of extraction efficiencies of the target drugs by the two proposed sorbents, as well as GO nanosheets and PCL nanofibers, was accomplished to study the types of interactions as well as the adsorption mechanism. The results revealed that GO/Al-30 NC, having many polar and anion exchange sites caused by Al-30 polyoxocations, is a good selective sorbent for acidic polar compounds which their extraction by nonpolar sorbents is not desirable. Additionally, GO/Al-30 NC-PCL nanofibers exhibited extraction capability for a wide range of compounds from acidic polar to nonpolar and nonionizable ones.