Comparative study of thermal reflux and microwave-assisted functionalization of Luffa cylindrica with CTAB for...

This study compared the functionalization of Luffa cylindrica (LC) with cetyltrimethylammonium bromide (CTAB) via thermal reflux (LC-CTAB-R) and microwave-assisted (LC-CTAB-M) methods to enhance the biosorption of anionic dyes methyl orange (MO) and indigo carmine (IC). Surface characterization (FTIR, SEM, EDX, pHpzc, Boehm titration) confirmed successful CTAB incorporation, with microwave-treated LC exhibiting finer agglomerates (~3.8 µm), higher nitrogen content (10.38% vs. 3.28%), and a more acidic surface (pHpzc = 5.21 vs. 5.74). Thermal analysis (TGA/DSC) indicated improved stability. Dynamic column experiments assessed initial dye concentration (20-80 mg·L⁻¹), biosorbent mass (2-6 g), NaCl (6.25 g·L⁻¹), SDBS (0.8 g·L⁻¹), and ten adsorption-desorption cycles. Raw LC showed limited removal (IC 36-51%, MO 33-44%), whereas LC-CTAB-R achieved IC 65-77.8% and MO 61-73.8%, and LC-CTAB-M reached IC 69-90% and MO 67-84.8%, with total desorbed amounts > 20 mg. Higher biosorbent mass increased total uptake (q_tot up to 77 mg IC, 70 mg MO) but lowered equilibrium capacity (q_eq). NaCl and SDBS affected raw LC significantly (IC/MO 20-36%/17-33% and 17/14%), but CTAB-modified fibers maintained > 61%-68% retention. Ten cycles confirmed excellent regeneration, with LC-CTAB-M retaining > 98% efficiency. These results demonstrate that microwave-assisted CTAB functionalization is rapid (2 min), energy-efficient, and produces a high-performance, regenerable biosorbent with strong electrostatic interactions, selectivity, and resistance to competitive conditions, suitable for treating multicomponent dye-laden industrial effluents.