An eco-friendly sorption-spectrophotometric method for Pb(II) determination in wastewater based on methyl thymol blue immobilized on silk fibroin.

Lead is a highly toxic heavy metal, and its accurate determination in environmental water is essential for public health and environmental protection. In this study, a simple, sensitive, and eco-friendly sorption-spectrophotometric method was developed for the determination of Pb(II) ions using methyl thymol blue (MTB) immobilized on natural silk fibroin fiber. Silk fibroin waste was selected as a sustainable and low-cost support material because of its high sorption capacity, chemical stability, and availability as a secondary raw material. The immobilization conditions of MTB and the complexation behavior of Pb(II) ions were systematically optimized. The maximum analytical signal was observed at pH 5.5, and the Pb(II)-MTB complex exhibited an absorption maximum at 610 nm. Under the optimal conditions, the method showed good linearity in the concentration range of 2.5-35 μg/50 ml with a correlation coefficient (R2) of 0.995. The low detection and quantification limits confirmed the high sensitivity of the proposed method. The immobilization process and complex formation were characterized by UV-Vis spectrophotometry, Raman spectroscopy, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS), confirming the stable binding of Pb(II) ions to the immobilized reagent. The method was successfully applied to industrial wastewater samples from the Shurtan Oil and Gas Production Department. Comparative analysis with ICP-AES demonstrated good agreement and confirmed the accuracy and reliability of the developed method. The proposed approach is inexpensive, reusable, environmentally friendly, and suitable for routine monitoring of Pb(II) contamination in water samples.