Spectroscopic and elemental evaluation of Pb(II), Cu(II), and Hg(II) binding by salvia officinalis L. leaf extract

Heavy metal contamination remains a major environmental concern because toxic ions such as Pb(II), Cu(II), and Hg(II) persist in ecosystems and pose serious risks to the environment and human health. Plant-derived extracts rich in phenolic acids, flavonoids, and other heteroatom-containing phytochemicals offer a promising natural matrix for metal binding through hydroxyl, carbonyl, and C-O-containing functional groups. This study presents a comparative matrix-level evaluation of interactions of Pb(II), Cu(II), and Hg(II) with Salvia officinalis L. leaf extract by integrating UV-Vis spectroscopic stoichiometry, apparent binding analysis, pH- and temperature-dependent spectral responses, EDTA-assisted reversibility, FTIR functional group assignments, and ICP-OES-based elemental validation. UV-Vis data were evaluated using Job's plot analysis, while apparent binding parameters were estimated using the extended Benesi-Hildebrand and Scatchard models, based on the observed stoichiometric behaviour. Pb(II) and Hg(II) exhibited apparent M₂L-type interaction patterns, whereas Cu(II) showed a 1:1 binding mode. Among the tested ions, Hg(II) produced the strongest spectroscopic binding response, followed by Pb(II) and Cu(II). The metal-extract interactions were strongly affected by pH and temperature, with more pronounced spectral responses under mildly alkaline conditions and at temperatures above 45 °C. EDTA addition indicated that the binding process was at least partially reversible, suggesting the potential regeneration of the extract-based metal-binding system. ICP-OES analysis supported the incorporation of metals into the extract-derived complexes, whereas changes in FTIR spectra indicated the involvement of hydroxyl, carbonyl, and C-O groups in metal coordination. Overall, the findings demonstrate the metal-dependent binding behavior of S. officinalis leaf extract and provide a useful spectroscopic and elemental basis for further studies on plant-derived metal-binding systems.