Towards zero-wastewaters treatment: biogenic composite for targeted dye congo red adsorption

Abstract

This study employed analysis of variance (ANOVA) within the framework of response surface methodology (RSM) to optimize the adsorption of Congo red dye using a novel nanocomposite adsorbent. Bp/CNTs@CS, synthesized by integrating carbon nanotubes and chitosan onto banana peel-derived activated carbon. The adsorbent was thoroughly characterized using FTIR, BET, XRD, SEM, and TGA analyses. The SEM image demonstrates a scaffold-like structure with layered layers, indicating that the carbon nanotubes and chitosan were successfully incorporated into the activated carbon matrix, whereas, FTIR findings confirm the successful integration of CNTs and Cs into activated carbon, leading to the formation of the Bp-CNTs@Cs hybrid material. The adsorption data aligned well with a quadratic regression model (p < 0.05), validating its predictive strength. Optimal conditions (15.302 mg/L dye concentration, 84.75 min contact time, pH 3.4, and 23.84 mg adsorbent dosage) resulted in a 95.254% removal efficiency. Adsorption performance decreased at pH above 3, while longer contact time and higher dosage improved efficiency. The process followed the Temkin isotherm, indicating a linear decline in adsorption heat and pseudo-second-order kinetics, confirming chemisorption as the primary mechanism. The nanocomposite achieved a maximum dye uptake of 98.993 mg/g, with an adsorption energy > 0.008 J/mol, and thermodynamic analysis confirmed the process to be spontaneous and endothermic. Under ideal conditions (temperature: 25 ± 5 °C; pH: 3.0), a batch-mode scale-up design shows that adding an estimated 52 g of Bp/CNTs@CS nanocomposite can result in a 95% CR dye removal for 50.0 L of wastewater sample. The adsorbent maintained high efficiency across five regeneration cycles. Mechanistic studies revealed that adsorption was governed by electrostatic interactions, π–π stacking, hydrogen bonding, and physical entrapment within the porous structure.