Experimental, DFT and MD simulation combined studies for the competitive adsorption of anionic and cationic dyes on activated carbon in an aqueous medium

The research purpose of this work is to examine the adsorption interaction of synthetic dyes, such as methyl blue (MeB) and methyl orange (MeO), with the commercial activated carbon (CAC) (001) surface, in various mediums. Molecular dynamic (MD) simulations and density functional theory (DFT) calculations were used to explore the adsorption mechanism of these dyes on the CAC (001) surface. Experimental analysis is very suitable for understanding adsorption, but they are commonly expensive and time-consuming. With the improvement of computer hardware and software, DFT and MD simulation methods in recent times have become fast and powerful tools for predicting dye removal and understanding their adsorption mechanisms. The experimental results showed that the removal of both dyes followed the Langmuir isotherm, and the R2 correlation coefficient values for MeO and MeB dyes were 0.993 and 0.988 respectively. The maximum adsorption capabilities for MeO and MeB dyes were 229.89 and 312.39 mg.g−1, respectively. DFT obtained results showed that the MeB dye is more reactive than the MeO dye and would have a better capacity for adsorption than the MeO molecule. The comparative investigation based on low-energy electronic structures revealed that the influence of molecular structure on the electron donating/accepting ability determines the trend of adsorption potentials. MD simulation was used to look into the most suitable adsorption configurations of MeB and MeO molecules. The MD simulation-calculated adsorption energies demonstrated that the CAC (001) surface had a strong affinity for the cationic dye in a basic medium and high sensitivity to interactions with the anionic dye in an acidic solution. The outcomes demonstrated that dyes formed covalent connections with functional groups and C atoms of studied adsorbent to be better adsorbed on the CAC surface. Theoretical concepts from this work could serve as a reference for researchers looking into the usage of CAC adsorbent in the treatment of water contamination. Theoretically, computational modeling allowed for the confirmation of experimental findings and the identification of the optimal azo dye adsorption configuration on the employed activated carbon.