Schiff bases from Sodium alginate and o-phenylenediamine as a water-soluble fluorescent copper(II) chemosensor

Polymeric Schiff bases derived from aromatic diamines have attracted significant interest due to their potential applications as fluorescent chemosensors. In this study, polymeric Schiff bases were synthesized from oxidized alginates (oxidation degrees of 20%, 40%, and 60%) and o-phenylenediamine. 1 H-NMR and FT-IR confirmed the chemical changes produced in all synthesized polymers. Rheological analysis revealed that the oxidized alginates exhibited Newtonian behavior, with a marked reduction of their thixotropy. In contrast, the synthesized Schiff bases exhibited a slight recovery in viscosity and thixotropic behavior, along with viscoelastic characteristics. All Schiff bases presented a fluorescence emission at nearly 370 nm in aqueous solution, and their fluorescence quenching responses toward Zn 2+ , Co 2+ , Ni 2+ and Cu 2+ ions were evaluated. OSA 20%-OPD exhibited the strongest response to Cu 2+ ; this Schiff base reached a limit of detection of 22.1 μM and a limit of quantification of 73.8 μM, while the Stern-Volmer analysis indicated a static-dynamic fluorescence quenching mechanism between the polymer and Cu 2+. This study offers valuable results of a new water-soluble fluorescent chemosensor for the detection of Cu 2+ .