Study of Triangular Silver Nanoplates for the Detection of Trace Lead Ions

Abstract

In an acidic medium (pH 2.56), the silver atoms at the three vertices of triangular silver nanosheets (TAg-NPs) are highly active, making them prone to oxidation by oxygen in the air, which converts them into Ag⁺. This oxidation alters the morphology of TAg-NPs from triangles to disk or spherical shapes, resulting in a blue shift in the maximum absorption wavelength (λ_max) of TAg-NPs. However, in Britton –Robison buffer solution (BR) at pH 2.56, when a small amount of Pb²⁺ is present in the solution, the \({\text{PO}}_{4}^{{3 - }}\) ionized from the BR can react with Pb²⁺ to produce Pb₃(PO₄)₂ precipitates, which adhere to the surface and vertices of TAg-NPs, leading to aggregation among them, subsequently inhibiting the corrosion of TAg-NPs in the acidic medium. Moreover, the negatively charged phosphate ions (\({\text{PO}}_{4}^{{3 - }}\)) can attract multiple cations simultaneously. For instance, two \({\text{PO}}_{4}^{{3 - }}\) ions can react with three Pb²⁺ ions to form a larger complex, causing the TAg-NPs to aggregate. Consequently, both the morphology and the maximum absorption wavelength of TAg-NPs undergo significant changes as the concentration of Pb²⁺ increases in the presence of BR at pH 2.56. Consequently, the color of TAg-NPs shifts gradually, and the change in maximum absorption wavelength (Δλ) between TAg-NPs/Pb²⁺/BR and TAg-NPs/BR solutions correlates with the concentration of Pb²⁺. Based on this, a new method for detecting Pb²⁺ has been established that is simple, rapid, and sensitive.