Computational study of the interaction between azo dye (RR141) and Hematite α-Fe2O3(1 1 1) Surface: Density functional theory and molecular dynamics simulation

Abstract

The adsorptive removal of azo dye molecules from textile effluents by the powdered mineral hematite has been largely studied in the literature, but this mechanism of interaction with the mineral hematite surface is still to date not revealed, hence the need for a theoretical study. The crystal structure model of Hematite adopted is α-Fe2O3 (111). The density functional theory and molecular dynamics simulation have been used to elucidate the mechanism of interaction. The azo dye molecule chosen for this study is the reactive red RR141. Geometry optimization of RR141 was performed at the DFT/B3LYP/6–31++g(d,p) level of theory. The reactivity and performance of RR141 in isolated form and in aqueous media were studied based on their degree of planarity, global and local electronic proprieties as well as their deformation capacity to adhere to the mineral surface. The Azo (>NN < ) and hydroxyl (-OH) groups are the main active centers for the adsorption of RR141 in isolated form and aqueous media. Azo and hydroxyl groups of RR141 dye are electron donors, while the sulphonic acid (-SO3--Na+) group is an electron acceptor. The RR141 is found more reactive in the vacuum than in an aqueous medium. The interfacial interaction is the combined effect of the hydrogen bond and the interactions between Fe & -O-, C, -S- and = N- atoms. The whole system interacts with the first layer through (π- π) bonding in the almost parallel adsorption geometries and through lone-pair electrons of hetero-atoms.