Selective colorimetric detection of Pb²⁺ using Ag nanoparticles encapsulated in CMC

This study presents a novel approach for the selective colorimetric sensing of Pb²⁺ in aqueous solutions. Green-synthesized silver nanoparticles in a carboxymethyl cellulose matrix (AgNPs/CMC) were created using a UV-irradiation technique. The successful formation of AgNPs/CMC was thoroughly examined using UV–vis, X-ray photoelectron spectroscopy, X-ray diffraction, transmission electron microscope, and Fourier transform infrared spectroscopy. AgNPs enhance Pb²⁺ detection through a synergistic effect with CMC’s complexation ability, enabling sensitive and accurate detection of environmentally relevant Pb²⁺ concentrations (5.0 × 10⁻⁵ to 1.0 × 10⁻⁷ M). Upon adding Pb²⁺, the UV absorption intensity of the longitudinal band diminished and blueshifted, with an observable color change. This indicates that AgNPs assembled side by side due to electrostatic interactions between the positive charge of Pb²⁺ and the negative charges of OH and carboxyl groups in CMC. The observed shift in plasmon absorption resulted from the organization of AgNPs at a supramolecular level. The unique coordination behavior of Pb²⁺ enables the formation of a stable supramolecular complex, leading to plasmon coupling and a visible color change. This suggests that the interaction between Pb²⁺ and CMC likely occurs through a T-Pb²⁺-T bond, causing the aggregation of AgNPs.