Optimization of Reactive Black 5 biosorption using TTAB-modified montmorillonite clay encapsulated in pectin/alginate composite membrane: A response surface methodology approach

• Pectin/alginate composite membrane with TTAB-modified montmorillonite clay was developed for Reactive Black 5 (RB5) dye removal • Optimized adsorption conditions were determined using Response Surface Methodology, achieving 86.17 mg/g capacity at 300 mg/L, pH 10, and 30°C • Structural and chemical characterization using SEM, FTIR, XRD, and EDS confirmed successful dye adsorption • Efficient desorption and reusability with 95.97% dye recovery using 0.1 M NaOH, though adsorption capacity declined after reuse • Biodegradable and cost-effective material with potential for industrial-scale wastewater treatment applications This study developed a pectin/alginate-based composite membrane embedded with tetradecyltrimethylammonium bromide (TTAB)-modified montmorillonite clay (TTAB-clay) for the effective removal of Reactive Black 5 (RB5) dye from aqueous solutions. Batch biosorption experiments were conducted to investigate the influence of contact time, pH, initial dye concentration, and temperature. Equilibrium was reached within 180 min. Process optimization was performed using Response Surface Methodology (RSM) based on the Box–Behnken Design (BBD), identifying the optimal conditions as 300 mg/L RB5 at pH 10 and 30 °C, achieving a maximum biosorption capacity of 86.17 mg/g. The fitted RSM model exhibited good predictive accuracy, with an R² value of 0.8644. Kinetic analysis revealed that the biosorption followed a pseudo-second-order model, while isotherm data were best described by the Langmuir model, indicating monolayer adsorption on a homogeneous surface. Surface analyses supported successful dye capture: EDS detected sulfur on the spent membrane, and FTIR revealed downshifts of O-H and carboxylate bands together with enhanced signals in the S=O region, evidencing hydrogen bonding and electrostatic interactions between RB5 sulfonate groups and the polymer/TTAB-clay interface. NaOH provided the highest desorption efficiency. However, the membrane retained its structural integrity for only a single regeneration cycle, thereby limiting its practical reusability and motivating further mechanical reinforcement and regeneration-stability optimization.