Dye degradation and molecular docking mechanism of Terminalia catappa mediated mesoporous titanium dioxide nanoparticles

Abstract

Mesoporous titanium dioxide nanoparticles (TiO2NPs) were evaluated for their adsorption capacity and the mechanism of rhodamine B (RhB) and congo red (CR) removal using molecular docking with density function theory (DFT). Mesoporous TiO2NPs had a pH point of zero charge at pH 7.45 and maximum adsorption occurred at pH 9 and 3 for RhB and CR, respectively. Based on the correlation coefficient (R2) and the root square mean error (RMSE), the Langmuir model was the most appropriate isotherm and pseudo-second-order was the most accurate kinetic mechanism. Adsorption of RhB and CR was feasible, exothermic, physical, and spontaneous, with maximum adsorption capacities of 389.74 and 244.57 mg g-1, respectively. Adsorption, as predicted by molecular docking (DFT), was exergonic involving electron transfer mechanism from RhB and CR to TiO2NPs. The interactions between Ti and RhB-O and CR-N atoms were found to be more significant than those between Ti and the phenyl-H and -C atoms of the dyes. Three complexes were predicted for RhB based on energy and interatomic distances, and two for CR. In this study, an alternative reusable adsorbent that is more effective at removing RhB and CR was biologically synthesized with an identified mechanism.