Removal of cationic dye from coloured water by adsorption onto hematite-humic acid composite: Experimental and theoretical studies

Abstract

An application has been studied of the hematite-humic acid (hematite-HA) composite as an efficient adsorbent of crystal violet dye (CV dye) as a model pollutant. The XRD, FTIR, Microelectrophoresis, SEM-EDX and EDS-Elemental Mapping techniques have been used to characterise the hematite-HA composite. The adsorption tests of CV dye onto hematite-HA composite were studied as a function of various physicochemical parameters. The experimental data shows that the covering of the hematite particles by humic acid ameliorates highly increase the CV dye removal from aqueous solution. The results of the sorption kinetics and isotherm model indicated that the adsorption kinetic was well fitted by the pseudo-second-order model, and the Temkin model fit the equilibrium data better. The CV dye removal effectiveness by hematite-HA composite achieved 97 %. A theoretical investigation of the potential reaction between Hematite-HA composite and CV dye was realised by determining some quantum and energetic parameters. The DFT calculations and Monte Carlo simulation were used to study the adsorption mechanism of the CV molecule onto hematite-HA composite. The calculated quantum parameters such as optimised structure, HOMO, LUMO frontier orbitals, and ESP were determined to describe the electron density for the HA model, therefore, simplifying the understanding of their reaction behaviour. Besides, the fluctuation energy curves, the probability of the adsorption energy distributions, and the geometry of the lowest adsorption energy pose for CV/Hematite, HA/Hematite, and CV/HA/Hematite surface are also calculated using the Monte Carlo simulation method. These results present the optimal conditions by equilibrium statistical that allows explaining the description of the adsorption mechanism behaviours between Hematite-HA composite and CV dye. The theoretical outcomes are in good agreement with the experimental results.