Biosorption of Crystal Violet onto Fenugreek Seed Powder: Comprehensive Optimization Through Response Surface Methodology and Elucidation of Dye Uptake Mechanism

This work investigates the efficacy of fenugreek seed powder (FSP), an agricultural product, as an economical and sustainable biosorbent for the extraction of crystal violet (CV) dye from aqueous environments. The biosorbent was analyzed using XRD, FTIR, and SEM-EDX, validating its amorphous structure, surface functional groups, and porous shape. Batch biosorption tests were adjusted utilizing a Box–Behnken design (BBD), incorporating three independent variables: FSP dose (0.02–0.1 g/100 mL), pH (4–10), and time (5–60 min). The model exhibited exceptional prediction accuracy (R² = 0.99, CV = 2.12%) and recognized all three variables as statistically significant (p < 0.05). The maximum CV removal attained was 91.8% efficiency at an FSP dose of 0.1 g/100 mL, pH 7, and a time of 60 minutes. FTIR examination indicated changes in the –OH, C=O, and C–O functional groups, signifying their participation in dye interaction, whilst SEM pictures validated dye deposition on the biosorbent surface. The biosorption process was ascribed to electrostatic forces, hydrogen bonding, π–π stacking, and pore filling. These findings underscore FSP as a viable, economical biosorbent for the removal of cationic dyes in wastewater treatment applications.