Evaluation of Chitosan and 1,8-Dihydroxyanthraquinone Schiff Base as a Fluorescent Sensor for Transition-Metal Ions

The current research aims to demonstrate the potential of C-DHQ fluorophore synthesized from biopolymer chitosan and 1,8-dihydroxyanthraquinone through Schiff base reaction as a sensor for detection of metal ions through fluorescence technique. The condensation reaction between the amine group of chitosan and the carbonyl group of 1,8-dihydroxyanthraquinone results in the formation of an imine linkage that facilitates the covalent bonding of the anthraquinone derivative to the chitosan backbone. The synthesis of the Schiff base of chitosan is confirmed by employing techniques such as FTIR, TGA, scanning electron microscope, EDX, PXRD, absorption, and fluorescence spectroscopy analysis. The meticulous investigation of elemental quantification and surface morphology provides substantial evidence of the structural alterations for C-DHQ. The prominent peaks in UV–visible spectra of C-DHQ are at 222, 253, and 430 nm, corresponding to various electronic transitions such as n–π* and conjugated π–π*. The fluorescence spectra show emission maxima at 567 nm, which is further used to check the sensing efficiency of C-DHQ toward different metal ions and anions. The fluorescence analysis results demonstrate that among various transition metals studies in response investigation, Fe³⁺ metal ions can quench C-DHQ's fluorescence. Applying the fluorometric approach at different concentrations reveal that C-DHQ has a good selectivity, even at ppm level. The study also assesses the impact of varying the pH range of the Fe³⁺ ion solution on the fluorescence intensity of C-DHQ to optimize the condition for facile detection. Moreover, no interference for other metal ions is found for C-DHQ, supporting Fe³⁺ ions as fluoroprobe.