Enhancing Zn(ii) adsorption efficiency of alginic acid through pyridine-2-imine functionalization: kinetic, isotherm, and mechanistic insights

Abstract

This study investigates the functionalization of alginic acid (AA) with pyridine-2-imine (PAA) through a two-step reaction involving coupling and condensation. The objective was to enhance the Zn(II) adsorption efficiency of alginic acid. The PAA derivative was characterized to assess the extent of functionalization, changes in functional groups, surface morphology, and thermal decomposition behavior. Batch adsorption studies revealed a significant improvement in Zn(II) adsorption efficiency, with PAA achieving 83.36 mg g⁻¹, compared to 44.28 mg g⁻¹ for unmodified AA. The adsorption of Zn(II) on PAA was found to follow the pseudo-second order kinetic model, with equilibrium data fitting both Langmuir and Freundlich isotherms. Mechanistic analysis using FTIR and ¹³C CP-MAS NMR spectroscopy indicated that Zn(II) binds exclusively to the carboxyl group in AA, while in PAA, it binds to both the amide and imine groups, explaining the enhanced adsorption efficiency. These findings demonstrate that pyridine-2-imine functionalization significantly improves the Zn(II) adsorption capacity of AA from aqueous solutions. Future research could focus on optimizing the functionalization process and exploring its application in real-world water treatment systems.