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

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.