Xanthated Arbutus Pavarii leaves as a novel biosorbent for methyl violet 6B: A comparative nonlinear regression approach for kinetic isotherm, and thermodynamic modeling

Methyl violet 6B (MV 6B) poses significant environmental risks due to its persistence and carcinogenicity, creating an urgent need for sustainable removal technologies. This study addresses the demand for regionally adapted solutions by reporting the first-time valorization of Arbutus pavarii leaves, an endemic Libyan species, into a novel xanthated biosorbent i.e., Modified Arbutus Pavarii Leaves (MAPL). Sequential acid pretreatment and alkali-mediated xanthation successfully engineered a macroporous matrix, as confirmed by SEM, FTIR, BET, and XRD analyses, which revealed a transition from a low-porosity precursor to a rough, amorphous structure enriched with active xanthate (–C–S–) and hydroxyl functionalities. Under optimized conditions (pH 6, 0.02 g per 100 mL), MAPL achieved a competitive adsorption capacity of 228.3 mg g −1 . Analytically, the adsorption behavior extended beyond simple electrostatic models; significant uptake occurred near the point of zero charge (pHpzc ≈ 6.0). As suggested by pH-dependent behavior and functional group analysis, this observation points to the potential involvement of non-covalent interactions such as hydrogen bonding and π - π stacking as complementary driving forces when electrostatic repulsion is minimized. To ensure methodological rigor, this study moved beyond traditional linearization, employing nonlinear regression analysis validated by seven distinct error functions. This approach identified the pseudo-second-order kinetic model and the five-parameter Fritz–Schlunder isotherm as the superior descriptors, confirming a complex, multi-site adsorption process on a heterogeneous surface. Thermodynamic parameters indicated a spontaneous, endothermic, and entropy-driven process. With >83 % efficiency retained after five regeneration cycles, MAPL is established as a scientifically validated, low-cost, and renewable candidate for decentralized wastewater remediation. • APLP from Arbutus pavarii was developed as a novel low-cost biosorbent. • MV 6B dye removal achieved a high capacity of 228.33 mg g −1 at pH 6. • Nonlinear regression models outperformed linear ones for data fitting. • Pseudo-second-order and Fritz-Schlünder models fit adsorption best. • Adsorption is spontaneous, endothermic, and increases interfacial entropy.