Selective removal of hard metal ions from water using benzo-crown ether derivatives: A lewis acid-base interaction approach

Abstract

The hydrophilic internal cavities of crown ethers are enable complexation with metal ions, while their apolar exterior allows operation in organic solvents. In this study, benzo-thio-oxa crown ether derivatives (C1 and C2), synthesized via microwave-assisted methods, were evaluated for the extraction of metal ions from tap and stream water samples collected from Siirt and & Scedil;& imath;rnak provinces using liquid-liquid ion-pair extraction. The ligands showed preferential extraction toward selected metal ions depending on their donor atom composition and macrocyclic structure. For this purpose, benzothia crown ether compounds (C1 and C2) obtained by the microwave-assisted synthesis method were tested on tap and stream water samples (Samples I-III) taken from Siirt and & Scedil;& imath;rnak provinces by the liquid-liquid ion pair extraction method. While compound C1 (bis(1,2-dibenzo)octathio tetracarbonyl-36-crown-8) has fewer ether bridges and one thioether group, compound C2 (bis(1,2-dibenzo)tetrathio tetracarbonyl-42-crown-10) shows selectivity towards different ions, as it contains more ether bridges and one ester group. While C1 removes especially iron (total Fe) with high efficiency, compound C2 exhibited higher extraction efficiency against metal ions such as Zn2+, Ca2+, Sb3+, Mg2+, Mn2+, and Ni2+. Furthermore, partial decreases in anions such as F-, PO4 3-, SO4 2-, and NO3 - were observed following metal ion extraction, indicating concurrent changes in the ionic composition of the water samples. Post-treatment conductivity measurements indicated a 3-13% decrease in total dissolved ionic content. These findings underline the structure-function relationship of benzo-crown ether derivatives and indicate their potential use as tunable systems for selective metal ion removal, with possible future integration into water treatment materials.