Removal of two cationic dyes from aqueous solutions by adsorption onto local clay: experimental and theoretical study using DFT method

The main objective of this study was to investigate the potential of Natural Safiot Clay (NSC) obtained from Safi city (Morocco), as an adsorbent for the removal of two cationic dyes such as Basic Blue 9 (BB9) and Basic Yellow 28 (BY28) from single and binary systems in aqueous solutions. Natural safiot clay was characterised using different physical-chemical methods, including X-ray fluorescence, Energy Dispersive X-ray spectroscopy (EDX), Fourier Transform Infrared (FT-IR) and pH of the point of zero charge (pH(ZPC)). X-ray fluorescence results indicate high percentages of SiO2 (47.44%) and Al2O3 (31.24%). FT-IR spectrum identified kaolinite as the major mineral phase in the presence of quartz, calcite, and dolomite. The effects of various experimental parameters, such as initial dye concentration, adsorbent dose, initial pH and contact time on the adsorption extent were investigated and examined in a batch mode. For both dyes and in single and binary systems, the dye removal efficiency increases with increasing adsorbent dose, decreases with increasing initial dye concentration and varied with dye solution pH. Moreover, the experimental results indicate that the Langmuir model and the pseudo-second-order provide the best correlation of the experimental data in the two systems studied. The electrophilicity power of dyes affects the removal efficiency. The theoretical study proves that BB9 (omega = 6.178) is more electrophilic than BY28 (omega = 2.480), and more interactions with surface sites in the single and binary system with a removal efficiency of 96.20% to 95.57% and 85.32% to 61.48% for BB9 and BY28, respectively. The theoretical results are in good accordance with the experimental data reported.