Macromolecule–Adsorbent Interaction Study for the Removal of Azo Dye Using Local Activated Carbon: Isotherms, Kinetics, and Thermodynamics

Abstract

The adsorptive removal of a synthesized azo dye (N8) using locally produced activated carbon was investigated under various physicochemical conditions to evaluate its macromolecular interaction behavior. An adsorbent dose of 0.04 g per 25 mL achieved a removal efficiency of 83.4%. The Langmuir isotherm model yielded a maximum monolayer adsorption capacity of Qmax = 40.32 mg/g with KL = 6.70 L/mg (R 2 = 0.9978), while the Freundlich model showed strong agreement, with Kf = 40.59 mg/g and n = 1.63 (R 2 = 0.9985). Equilibrium was reached within 15 min, and kinetic analysis confirmed the pseudo‐second‐order model with k 2 = 0.015 g·mg −1 ·min −1 and qe(calc) = 62.11 mg/g (R 2 = 0.9997). Thermodynamic parameters indicated spontaneous and exothermic adsorption, with ΔH° = −31.50 kJ/mol, ΔG° values between −6.38 and −7.98 kJ/mol (293–333 K), and ΔS° = −79.36 J·mol −1 ·K −1 . The adsorption efficiency decreased with increasing temperature, consistent with exothermic physisorption. Optimal removal occurred at pH 6–7, 298 K, 0.04 g adsorbent dose, 100 mg/L dye concentration, and 15 min contact time. These results confirm that locally produced activated carbon provides an efficient, economical, and macroscopically robust adsorptive platform for azo dye removal from aqueous media.