Competitive liquid–liquid extraction of metal ions with novel pyridinyl-substituted benzothioate: Experimental studies, real matrix applications and DFT insights

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In this study, the selectivity of the compound S,S'-di(2-pyridinyl)-2,2'-dithiodibenzothioate from media containing a mixture of metal ions was investigated using competitive liquid-liquid ion pair extraction, and its metal removal properties were studied in real water matrices. Extraction experiments conducted with solutions containing mixtures of Zn²⁺, Mn²⁺, Cr³⁺, Fe³⁺, Co²⁺, and Cu²⁺ ions revealed that the ligand exhibited particularly high selectivity towards the Fe³⁺ ion. The variation in extraction data was determined by Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES), and the best extraction efficiency was obtained for the Fe³⁺ ion (44.12%). Relative selectivity factors showed that the ligand extracted the Fe³⁺ ion more efficiently than other metal ions. Furthermore, metal removal studies were conducted on lake, stream, and tap water samples to determine the performance of the compound in real water matrices, and ion exchange was detected by Inductively Coupled Plasma Mass Spectrometry (ICP-MS). The relationship between the electronic structure of the ligand and its extraction behavior was also investigated using density functional theory (DFT) calculations. The calculated HOMO–LUMO energy gap, chemical hardness, and other spherical reactivity parameters supported the strong interactions of the ligand, particularly with Fe³⁺ ions, which have a high charge density. The results indicate that S,S'-di(2-pyridinyl)-2,2'-dithiodibenzothioate can be used as a potential extraction agent for the selective removal of metal ions from environmental water samples.