From fig leaves to bentonite: engineering high-efficiency CTAB-modified adsorbents for sustainable dye removal

The discharge of untreated dye effluents, particularly from the textile industry, poses a significant environmental challenge due to the persistence and toxicity of synthetic dyes like methyl orange (MO). This study addresses the urgent need for sustainable and effective treatment solutions by developing and characterizing two novel, low-cost adsorbents: cetyltrimethylammonium bromide (CTAB)-modified bentonite (B-CTAB) and CTAB-modified fig leaf (Lf-CTAB). A comprehensive suite of analyses—including XRD, FT-IR, FESEM, TGA, and BET—confirmed the successful modification and revealed the enhanced surface properties of both materials. The adsorption performance was systematically optimized by evaluating critical parameters such as pH, initial MO concentration, contact time, temperature, and adsorbent dosage. Under optimal conditions (100 mg L ⁻¹ MO, 60 min, pH = 2, T = 298 K), both adsorbents exhibited high removal efficiency, achieving removal rates of 99.35% for B-CTAB and 99% for Lf–CTAB. The maximum adsorption capacities ( q _max ) were 400 and 250 mg g ⁻¹ for B-CTAB and Lf-CTAB, respectively. The adsorption isotherm and kinetic data were best described by the Langmuir ( R ²  ≈ 0.99) and pseudo-second-order models, respectively, suggesting a monolayer adsorption mechanism. Thermodynamic studies confirmed that the process was spontaneous and endothermic. Notably, both adsorbents exhibited excellent regeneration capability and maintained high efficiency over multiple reuse cycles, underscoring their economic and operational sustainability. This work highlights the great potential of these modified natural materials, especially the valorized fig leaf biomass, as efficient, renewable, and practical adsorbents for advanced wastewater treatment.