Schiff Base functionalized CMC/PVA composites for efficient adsorption of Cu(II) and Zn(II): From molecular design to economic evaluation

Metal contamination in water sources is a critical threat to human health and water ecosystems, which reduces the efficiency of water desalination. Therefore, the development of materials for metal removal is essential for water purification. In this study, two novel Schiff bases (LA35 and LH35) were immobilized in a carboxymethyl cellulose/polyvinyl alcohol (CMC/PVA) matrix via robust hydrogen bonding. The CMC/PVA-LA35 and CMC/PVA-LH35 composite adsorbents achieved a maximal adsorption of 474.38 mg/g and 532.15 mg/g for Cu(II) and 516.49 mg/g and 468.04 mg/g for Zn(II), respectively, at optimum conditions, pH 5, 318 K, and 300 mg/L. The data fit the Langmuir isotherm model, suggesting that adsorption occurred on a homogeneous mono-layer surface with uniform binding sites. Additionally, a thermodynamic analysis confirmed the reaction was both spontaneous and endothermic. After six cycles of adsorption/desorption, the CMC/PVA-LA35 and CMC/PVA-LH35 maintained outstanding reusability with efficiencies of 76.72% and 81.69% for Cu(II) and 71.33% and 67.32% for Zn(II), respectively. DFT calculations revealed effective metal-ligand interactions via charge transfer and reduced bandgap. These findings were consistent with the large experimental adsorption capacities and confirm the importance of chemisorption for Cu(II) and Zn(II) removal. These findings reveal that metal chelation strength and complexation control the adsorption process. The results of the cost-effectiveness analysis showed that the total cost of reusability was extremely low. This discovery unveils its potential use in water desalination, offering new bio-composites to decrease metal contamination and protect aquatic life.