Sequestration of methyl blue dye from aqueous solution onto raw and modified Banana (Musa paradisiaca) flower wastes

Synthetic dyes like methylene blue (MB) persist in aquatic environment and threaten human and animal health. Agricultural by-products like banana flower (BF) wastes can be converted into low-cost adsorbent for sustainable dye uptake. This study reveals the conversion of discarded banana flower (Musa paradisiaca) waste into an efficient and sustainable biosorbent for MB elimination from aqueous media. Acid modification was utilized to enhance the adsorption performance of raw banana flower (RBF), producing modified banana flower (MBF) with enhanced surface functionality and adsorption affinity. Surface and structural validation using XRD, SEM, FT-IR, and BET analyses confirmed the predominantly amorphous mesoporous structure and the presence of oxygen-containing functional groups such as -OH, C = O, and C-O responsible for dye binding. BET study revealed a surface area of 106.3 m²/g with a mesoporous structure (average pore diameter ≈ 6.1 nm), favorable for dye uptake. Batch adsorption experiments showed that MB uptake was strongly influenced by temperature, pH, contact time, and adsorbent dosage, with optimum adsorption occurring under alkaline conditions. Langmuir isotherm analysis showed maximum adsorption capacities of 29.9 mg/g for RBF and 48.6 mg/g for MBF, confirming the significant enhancement achieved through acid modification. The Pseudo-first-order model best described MB uptake by RBF (R² = 0.977), while pseudo-second-order model fits perfectly the kinetic data of MBF (R² = 0.988), while thermodynamic parameters confirmed a spontaneous (ΔG: -3.23 to -39.72 kJ/mol) and endothermic process (ΔH: + 23.38 and + 97.88 kJ/mol). The findings highlight the potential of acid-modified banana flower waste as a low-cost, eco-friendly, and high-performance adsorbent for sustainable wastewater treatment applications.