Synthesis and characterization of hydrogel-kaolin intercalation composite material and investigation of its use in Allura red adsorption: experimental and theoretical approaches

The presence of industrial dyes in wastewater poses a threat to human health and life. One of the dyes commonly found in industrial wastewater is Allura red (AR). Developing efficient and cost-effective adsorbents to remove AR dye from wastewater is a critical advance in this field. This study evaluated the synthesis of polyacrylamide-kaolin (PAA@K) composite and the investigation of its adsorbent properties. The structural properties of the PAA@K composite adsorbent were investigated using FT-IR, SEM, and EDX analyses. The maximum adsorption capacity for AR dye was determined as 383 mg g⁻¹ using the Langmuir model. Kinetic studies revealed that the adsorption process for AR dye followed the pseudo second order model. According to its thermodynamic properties, AR dye was found to adsorb spontaneously and endothermally on the PAA@K composite. Complementary theoretical studies using density functional theory (DFT) calculations provided information on the molecular interactions between the AR dye and the PAA@K composite. Accordingly, DFT calculations provided convincing evidence for robust binding interactions such as hydrogen bonds and electrostatic interactions between AR dye molecules and PAA@K composite. Experimental findings also agree with theoretical observations, confirming a significant relationship between them. This study highlights the importance of combining experimental data with theoretical models to advance the development of eco-friendly materials for treating colored pollutants in industrial wastewater.