**4. Conclusion**

The results obtained in this research indicated that natural safiot clay was considered low cost, eco-friendly, and a promising alternative adsorbent for removing BB9 and BY28 dyes in single and binary systems from an aqueous solution. The percentage of dye removed increased with increasing adsorbent dosage, decreased with increasing initial dye concentration, and varied with dye solution pH. The rate of adsorption was found to obey pseudo-second-order kinetics model with a good correlation coefficient indicating toward chemisorption, and the Langmuir isotherm represented the equilibrium adsorption and shows monolayer homogeneous surface of adsorbent for single and binary mixture.

All the theoretical parameters of DFT calculations show that the two dyes can be adsorbed and that the BB9 molecule has the best percentage of elimination. From this calculation, we note that: The dye removal efficiency increases with the highest values of ω, ELUMO, μ, and S and the lowest values of ΔEgap, EHOMO and η. Another important conclusion that we can draw from these calculations is that the theoretical results from reactivity descriptors show that nitrogen, sulfur, carbon, and nitrogen atoms of BB9 and BY28 are the main adsorption sites, respectively. Finally, this study displays a good correlation between the theoretical and experimental data, which confirm the reliability of the quantum chemical methods to study the competitive adsorption of two cationic dyes onto NSC surfaces, in the single and binary system. DFT calculations, Monte Carlo method, and Molecular dynamics simulations support the experimental findings.
