Performance of 2D MXene as an adsorbent for malachite green removal

The utilization of novel materials is one of the reliable solutions for wastewater remediation processes, where they could be applied as adsorbents. Among these materials, MXenes are increasingly used composites in different applications, including water treatment techniques, due to their exceptional properties that enhance the total performance. In this work, we used Ti₃C₂T_x MXene as an adsorbent for the Malachite Green dye removal, considering the dye's chromatic and leuco forms. Effects of adsorbent dose, pH, contact time, and dye's initial concentration on the removal efficiency were studied. Three adsorption isotherms, namely Freundlich, Langmuir, and Temkin, were studied to find the best fitting model with the practical results, where the Freundlich model had the highest R², 0.974. Furthermore, five kinetics models were used to study the adsorption kinetics; these are zero-order, pseudo-first-order, pseudo-second-order, Elovich, and intraparticle diffusion. However, the pseudo-second-order model showed the highest R² value of 0.999. It was found that as the adsorbent dose increases, the removal efficiency increases and reaches 94.1% when the dose was 0.09 g in a 50 ml solution. Interestingly, it was noticed that the removal efficiency increases as the pH increases or decreases; the minimum efficiency was noticed at pH = 6. This was attributed to the leuco nature of the dye; whereas the pH increases, the dye turns colorless and becomes hard to detect. This finding shows that the removal is high when the pH is low, and it is low as the pH gets high but cannot be detected because of the color loss. The removal efficiency dramatically increased as the contact time increased at first; however, at 60 min, it almost reached the study state and the follwoing change was marginal. Finally, the removal efficiency decreased as the dye's initial concentration increased.