Geopolymer composites derived from laterite and biochar from Ricinodendron heudelotii shells for the sequestration of Basic Fuchsin and Quinoline Yellow in aqueous phase

In this study, the geopolymer composites GP-LA, GP-LAC5 and GP-LAC10 were prepared from laterite substituted with 0%, 5%, and 10% biochar derived from Ricinodendron heudelotii shells, respectively, by alkaline activation. The materials were evaluated for adsorption of the cationic dye Basic Fuchsin (BF) and the anionic dye Quinoline Yellow (QY). The composites were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), N2 adsorption, iodine-number, and methylene-blue index measurements and scanning electron microscopy analyses. Batch adsorption experiments examined pH, adsorbent dosage, contact time and initial dye concentration. Biochar incorporation modified the geopolymer structure and increased the specific surface area from 37.33 ± 0.08 to 65.81 ± 0.08 m2 g−1. The Langmuir maximum capacities reached 56.70 ± 5.89 mg g−1 for BF and 45.88 ± 2.89 mg g−1 for QY. QY uptake was more closely associated with progressive textural development, whereas BF showed a stronger dependence on biochar fraction and surface chemistry; therefore, the two dyes did not respond identically to increasing surface area. Thermodynamic analysis indicated spontaneous adsorption and small enthalpy changes. The combined XRD, FTIR, BET, pHPZC, and kinetic evidence supports a proposed multimechanistic process involving electrostatic interactions together with hydrogen bonding, π–π interactions, electrostatic interactions, pore filling, van der Waals forces, and intraparticle diffusion. The results of this study have demonstrated the importance of combining the geopolymer with biochar derived from the husks of Ricinodendron heudelotii for the management of this waste and for the production of low-cost, environmentally friendly composites that are effective at removing cationic and anionic dyes.