Rapid, low-cost determination of Hg²⁺, Cu²⁺, and Fe³⁺ using a cellulose paper-based sensor and UV–vis method with silver nanoparticles synthesized with S. mammosum

As water effluents are often highly contaminated with metals, having a quick and cost-effective method of analysis is crucial. This study used the supernatant derived from the green synthesis of silver nanoparticles (AgNPs) with Solanum mammosum to detect mercury, copper, and iron with a low-cost cellulose paper-based sensor and a rapid colorimetric method applying ultraviolet–visible spectroscopy (UV–Vis). AgNPs in two precursor concentrations using silver nitrate, 1 mM (17.4 ± 9 nm) and 50 mM (and 22 ± 8.1 nm), were utilized to assess the efficacy of the analysis and removal of Hg²⁺, Cu²⁺, and Fe³⁺ from contaminated water. Cellulose paper-based sensor showed limits of detection (LODs) for Hg²⁺ of 2.46 and 123 μM using AgNPs at concentrations of 1 and 50 mM, respectively. For Cu²⁺, the LODs were 55 and 2750 μM, and for Fe³⁺, the LODs were 49 and 2470 μM using the respective concentrations. To differentiate and detect the cations with the naked eye, a potassium iodide and potassium ferrocyanide (1:1) aqueous solution was used, producing a yellow, pink, and blue color for Hg²⁺, Cu²⁺, and Fe³⁺, respectively. Additionally, the titration curves of Hg²⁺, Fe³⁺, and Cu²⁺ were examined by UV–Vis using the supernatant liquid. The LODs for the UV–Vis method using AgNPs at a concentration of 1 mM were 1.50 μM for Hg²⁺, 10.7 μM for Cu²⁺, and 4.33 μM for Fe³⁺, while the LODs for AgNPs at 50 mM were 5.75, 27.6, and 15 μM for Hg²⁺, Cu²⁺, and Fe³⁺, respectively. Furthermore, these nanoparticles were utilized to assess the efficacy of the removal of Hg²⁺, Cu²⁺, and Fe³⁺ from contaminated water. Removal efficiency with the solid 50 mM AgNPs was analyzed via flame absorption spectrophotometry; values over 95% were obtained for the three ions. The results underscore the effectiveness of a green synthesis approach to generating AgNPs, enabling efficient and economical cation analysis and water decontamination.