COMPLEXATION-DRIVEN REMOVAL OF Cr(III) AND Pb(II) IONS FROM AQUEOUS MEDIA USING A SCHIFF BASE LIGAND

Abstract

A Schiff base ligand, (E)-N¹-(2-hydroxybenzylidene)nicotinohydrazide (HNH), was synthesized via the reflux condensation of nicotinic acid hydrazide with salicylaldehyde. The ligand was evaluated for its sorption efficacy in the removal of Cr(III) and Pb(II) ions from aqueous solutions. Systematic studies were conducted to investigate the influence of key parameters, including contact time, solution pH, initial metal ion concentration, and temperature, on the adsorption performance of HNH. The experimental data were fitted to both Langmuir and Freundlich isotherm models, revealing favorable adsorption characteristics under the studied conditions. Thermodynamic analysis indicated that the sorption process was endothermic, with positive enthalpy changes (ΔH) of 115.81 kJ•mol⁻¹ for Cr(III) and 103.37 kJ•mol⁻¹ for Pb(II). Additionally, positive entropy values (ΔS) of 2.67 and 2.42 kJ•mol⁻¹•K⁻¹ for Cr(III) and Pb(II), respectively, suggest an increase in randomness at the solid solution interface. The negative Gibbs free energy values (ΔG) across all temperatures confirm the spontaneous and chemisorptive nature of the sorption process. These findings demonstrate that the HNH ligand is an efficient and thermodynamically favorable adsorbent for the remediation of Cr(III) and Pb(II) ions from contaminated water.