Fluorescence Naphthalene Cationic Schiff Base Reusable Paper as a Sensitive and Selective for Heavy Metals Cations...

Heavy metals are particularly damaging contaminants in the environment, and even trace concentrations represent a risk to human health due to their toxicity. To detect the heavy metals of Mn²⁺ and Co²⁺ ions, a novel selective reusable paper-based Fluorescence naked-eye sensor based on naphthalene cationic Schiff base (NCSB) was synthesized and confirmed using FT-IR, ¹ H-NMR, and MS tools. Based on a blue to colorless color change in the aqueous solution, the NCSB sensor is utilized to Mn²⁺ and Co²⁺ cations selectively among other metal ions (Fe²⁺, Cu²⁺, Mg²⁺, Ni²⁺, Zn²⁺, Cd²⁺, Hg²⁺, Pb²⁺, Sn²⁺ and Cr³⁺). In the aqueous medium, the NCSB sensor displayed high sensitivity, with limits of detection (LOD) values of 0.014 µM (14.08 nM) and 0.041 µM (41.47 nM) for Mn²⁺ and Co²⁺ cations, respectively. The paper-based sensor naked-eye detected Mn²⁺ and Co²⁺ cations in water at concentrations as low as 0.65 µM (65 nM) and 0.086 µM (86 nM), respectively. It was discovered that 5 min of incubation time and a pH range of 7 to 11 were optimal for the complexation reaction between the Mn²⁺ and Co²⁺ ions and the NCSB sensor. Through a static quenching process, the interaction of the different metal ions with the Schiff base group in the NCSB molecule results in the development of a ground-state non-fluorescent complex. NCSB sensor was also successfully applied in analysis of Mn²⁺ and Co²⁺ in environmental water with good recoveries of 94.8-105.9%. The theoretical calculations based on density functional theory (DFT) studies are in support of experimental interpretations. The links between the input factors and the anticipated response were evaluated using the quadratic model of the response surface methodology (RSM) modeling.