Eco-friendly one-step production of a highly sensitive fluorescent sensor for iron (III) detection in aqueous solutions: Experimental and DFT insights

Abstract

While ferric (Fe³⁺) ions are essential nutrients for biological systems, excessive concentrations can lead to toxic effects. Therefore, it is crucial to selectively detect Fe³⁺ ions in industrial effluents to regulate their levels and support environmental protection efforts. This work presents the development of 2-phthalimidobenzoic acid (PBA) as a novel fluorescent sensor, which exhibits high sensitivity and selectivity for detecting Fe³⁺ ions in aqueous solutions. PBA was synthesized through a straightforward, environmentally friendly process without using any organic solvent or catalyst via fusion of phthalic anhydride and anthranilic acid at 135 °C for only 10 min. Structure characterization was performed using both FTIR and NMR spectroscopy, while the crystal structure and thermal stability were assessed via XRD and TGA techniques. The optical properties of PBA were investigated using UV–vis and fluorescence spectroscopy at various pH levels. When excited at a wavelength of 336.6 nm, PBA exhibited a maximum emission peak at 405.4 nm. Using the Stern-Volmer equation, a strong correlation was observed between the concentration of Fe³⁺ ions and the fluorescence intensity of PBA, accompanied by a high quenching rate. The fluorescent sensor system demonstrated remarkable selectivity for Fe³⁺ ions over a wide range of tested metal ions and anions, with a significant reduction in fluorescence intensity in the presence of Fe³⁺ ions. UV–vis spectra before and after the addition of Fe³⁺ ions to PBA sensor exhibits a dynamic fluorescence quenching mechanism is occurring between PBA and Fe³⁺ ions. Additionally, DFT calculations provided atomistic insights into the sensing mechanism between Fe³⁺ and PBA. To further evaluate the practical applicability of the PBA sensor, five different real water samples were tested, yielding favorable results for Fe³⁺ detection.