Synthesis and Characterization of Kaolin–alumina Composite Adsorbent for Removal of Rhodamine B

In this study, a kaolin–alumina composite adsorbent was synthesized and characterized for the removal of Rhodamine B (RhB) from aqueous solutions. Kaolin clay was modified with Al₂O₃ using the sol–gel method to improve surface properties and enhance adsorption capacity. The resulting composite was characterized by SEM–EDX, XRD, FTIR, and N₂ adsorption–desorption analyses, which confirmed increased surface area and porosity compared to raw kaolin. Batch adsorption experiments were conducted to examine the effects of contact time, initial dye concentration, and adsorbent dosage on RhB removal efficiency. The adsorption process was optimized using Response Surface Methodology (RSM) with a Central Composite Design (CCD). Regression analysis indicated that the initial dye concentration was the most influential factor controlling removal efficiency. Equilibrium data were best described by the Sips isotherm model, with a maximum adsorption capacity of 37.38 mg g⁻¹. Kinetic analysis showed that the pseudo-nth-order model most accurately represented the adsorption mechanism. Thermodynamic evaluation confirmed that the process was spontaneous and exothermic. Overall, the kaolinite–alumina composite appears to be a promising and cost-effective adsorbent for the treatment of dye-contaminated wastewater.