Synthesis and Sorption Performance of Pyridyl-Based Imine and its Homocyclic Analogue toward Ni(II) and Cd(II) Ions in Aqueous Solution

Abstract

Nickel and cadmium are toxic heavy metals that pose serious environmental and health concerns due to their persistence and bioaccumulation. It commonly enters aquatic systems through industrial effluents, electroplating, mining, and the disposal of Ni-Cd batteries. Developing efficient sorbents for their removal from water is therefore of great importance. In this study, two imine derivatives were synthesized and evaluated as sorbents for Ni(II) and Cd(II) ions. The first derivative, 3,3′-dimethyl-[1,1′-biphenyl]-4,4′-diyl-bis-(1-(pyridin-2-yl) methanimine) (SB-1), was obtained from aryl diamine and pyridine-2-carboxaldehyde, while the second, 3,3′-dimethyl-[1,1′-biphenyl]-4,4′-diyl-bis-(1-phenylmethanimine) (SB-2), was synthesized using benzaldehyde. Both compounds were characterized by UV–Vis, FT-IR, FAB-MS, and ¹H-NMR spectroscopy. Batch adsorption experiments showed that SB-1 achieved maximum adsorption capacities (Qmax) of 16.89 mg/g for Ni(II) and 8.05 mg/g for Cd(II), while SB-2 recorded 12.66 mg/g and 7.42 mg/g, respectively, indicating higher efficiency of SB-1. The Langmuir model best described the adsorption data, suggesting monolayer adsorption on homogeneous surfaces, and RL values confirmed favorable sorption. Kinetic studies fitted well to the pseudo-second-order model, indicating chemisorption as the main mechanism. Thermodynamic analysis revealed that adsorption by SB-1 was spontaneous, irreversible, and endothermic, whereas SB-2 adsorption was spontaneous, reversible, and exothermic.