Remediation of the cationic dye Crystal Violet using <i>Olea oleaster</i> leaf biomass

This study evaluates the adsorption capabilities of <i>Olea oleaster</i> leaf extract residue for removing Crystal Violet (CV) dye from aqueous solutions. Fourier Transform Infrared analysis revealed diverse functional groups contributing to the material's hydrophilic nature and adsorption potential. Scanning electron microscopy images confirmed a porous, fibrous structure that transformed post-adsorption, indicating successful dye uptake. X-ray diffraction analysis identified crystalline cellulose forms enhancing adsorption stability, while energy dispersive X-ray analysis confirmed a significant increase in carbon content and incorporation of CV dye elements. Brunauer-Emmett-Teller analysis highlighted a moderate surface area of 6.42 m²/g, suitable for external adsorption processes. Kinetic studies revealed that adsorption equilibrium was achieved within 70 min, with a second-order model providing the best fit, indicating chemisorption. Optimal adsorption occurred at a biosorbent dose of 0.08 g, with efficiency diminishing at higher CV concentrations due to site saturation. Adsorption was most effective above the point of zero charge (pH 5.4), with temperature increases further enhancing adsorption capacity. Langmuir isotherm analysis suggested monolayer adsorption on a homogenous surface. The maximum adsorption capacity of the adsorbent was determined to be 44.24 and 66, 28 mg/g in the linear and nonlinear forms, respectively, highlighting its significant potential for the efficient removal of CV dye from aqueous solutions. Thermodynamic evaluations confirmed an endothermic and spontaneous process. Statistical modeling validated the system's reliability, offering a predictive framework for optimizing conditions. This work establishes <i>Olea oleaster</i> residue as a promising eco-friendly adsorbent for wastewater treatment.