Complexation–reduction method for the evolution of nanoparticles to detect Ag⁺ and Cu²⁺: a synergistic approach

Abstract

Schiff base compounds were reported to make a complex with Cu²⁺ and Ag⁺ and subsequent reduction produced Cu⁰ and Ag⁰ nanoparticles separately via UV irradiation. Here, we synthesized a Schiff base, which initially formed a complexation with Cu²⁺ and made Cu⁰ nanoparticles after 8 h aging. In that reaction mixture, addition of Ag⁺ resulted in Ag⁰ nanoparticles. Emissive semi-carbazone (a Schiff base synthesized from semicarbazide and salicylaldehyde) was employed for the first time to selectively and sensitively detect Cu²⁺ (linear range of detection 10^–4 to 5 × 10^–8 M and limit of detection 13 μM) with the formation of copper oxide nanoparticles via complexation–reduction method. The introduction of Ag⁺ in it produced Ag⁰ and Cu⁰ (CuO via aerial oxidation) nanoparticles with a gigantic increase of fluorescence to obtain selective and sensitive Ag⁺ detection (linear detection range 10^–3–10^–7 M, and limit of detection 7. 7 μM). Thus, Cu²⁺ and Ag⁺ were detected based on turn-off/on fluorescence in one pot. As the evolution of copper and silver nanoparticles was the fundamental reason for sensing, response time is similar to the stable fluorescence behavior of oxidized SC (cap** agent) with in situ generated copper and silver nanoparticles. CuO-induced fluorescence quenching was due to the formation of the trapped plasmon, while Ag⁺-induced fluorescence enhancement was owing to the lightning rod effect. The synergism of Cu and Ag was also investigated in this paper as a driving force of the lightning rod effect for the first time. Both the metals (Cu and Ag) were estimated in natural water, justifying the utility of the sensing platform for practical applications. Besides, the evolution of brilliant red color with semi-carbazone for Ag⁺ was employed for the colorimetric sensing of Ag⁺.