Sustainable Biocomposite-Based Nanosilica-Elaeis guineensis Shells (Ns-EGS) for the Biosorption of Acid Red 101 (Azocarmin G): Insight into Kinetics, Equilibrium, Thermodynamics, and Mechanistic Investigations

A novel biocomposite, Ns-EGS, was synthesized by combining nanosilica extracted from rice husks and Elaeis guineensis shells through the sol–gel method. This material was then used to remove the azo dye Azocarmin G from a simulated aqueous solution. X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and FTIR/TGA analysis characterized the biocomposite as having an amorphous and porous microstructure with a random distribution of nanosilica particles in the lignocellulosic matrix, showing the presence of various functional groups. The effect of contact time (0–120 min), adsorbent dose (0.05–0.3 g), initial dye concentration (25–150 mg/L), and initial pH (2.5–11) were investigated at three different temperatures (298 K, 312 K and 327 K). The results showed that adsorption was enhanced at acidic pH levels, with around a 90% removal rate achieved under optimal conditions. The experimental kinetic data preferentially fit the Hô model with an R2 = 0.999. This indicates that adsorption determines the process and shows an adsorbate–adsorbent affinity. The Langmuir model perfectly matched the equilibrium data with the highest correlation coefficient (R2) of 0.997 and the lowest value of RMSD. The monolayer adsorption capacity was found to be 128.21 mg/g at 327 K. The thermodynamic parameters revealed that the adsorption process is spontaneous (ΔG < 0) and endothermic (ΔH > 0). The low activation energy value of 15.62 kJ/mol, determined using the Arrhenius equation, suggests a physical adsorption process that involves weak Van der Waals and hydrogen-bond interactions.