Quantum mechanical study on physisorption of dissolved metal ions in seawater using cellulose, chitosan and chitin

Density Functional Theory (DFT) calculations were performed to investigate the adsorption of alkali and alkaline earth metal ions, Na+, K+, Mg2+, and Ca2+ present in seawater by biopolymers, cellulose, chitosan, and chitin. Analysis of the optimized geometries of the complexes formed by physisorption of metal ions on biopolymers reveals that monomer of chitin is the best biopolymer for adsorption of Mg2+ ion. Water as a solvent reduces the reactivity of complexes formed, playing a significant role in complex stability, which further proved the effective use of cellulose, chitosan and chitin for real-time applications. Natural Bond Orbital (NBO) analysis and quantum reactivity descriptors of the optimized geometries indicate that the electronic charge transfer between the biopolymer and metal ions acts as a driving force for the complex formation. This study also highlights the significant role of water in physisorption of metal ions on biopolymer.