THEORETICAL STUDY OF THE BONDING BETWEEN ALGINATE AND GRAPHENE OXIDE THROUGH THE INTERACTION OF ITS CARBOXYLIC GROUPS WITH THE DIVALENT METALS CU2+, CO2+, ZN2+, AND MN2+

The alginate-graphene oxide mixture has been extensively studied due to its capacity to adsorb heavy metals, presenting higher structural and thermal stability than alginate. These properties and adsorption capacity would be related to the presence of functional groups present in the hydrocarbon chain of alginate and graphene oxide, such as carboxylic, hydroxyl, ketone, and epoxy groups; in the present study, the interaction of transition cations in their divalent states Cu2+, Co2+, Zn(2+ )and Mn2+, which act as bridges when interacting with carboxylic groups of alginate and graphene oxide, was studied. Theoretical calculations based on density functional theory (DFT) were used for this purpose. For this, the lowest energy geometries were determined at the B3LYP level of theory through the effective central potential (ECP) with LanL2DZ bases. The chemical nature of the interactions under study was determined using the natural bond orbitals (NBO) method, topological analysis of the electronic location function (ELF), and the quantum theory of atoms in molecules (QTAIM). The results showed that the interactions between the metals under study with the carboxylic groups of alginate and graphene oxide are of the coordinated type with a high electrostatic component, which varies according to the metal, where the binding strength and stability, according to the degree of electronic delocalization, was as follows; ALG-Cu-GO > ALG-Co-GO > ALG-Mn-GO > ALG-Zn-GO. These results correlate with the available information, concerning the adsorption capacity of the alginate-graphene oxide mixture, for those metallic species. Furthermore, this interaction could influence the type of structural morphology of the alginate-graphene oxide beads.