Multifunctional copolymers for brilliant green dye removal: adsorption kinetics, isotherm and process optimization†

The presence of toxic dyes in water stream poses a significant environmental threat to human health and aquatic life. In this study, poly(AN-co-AMPS) was synthesized via free radical copolymerization and evaluated as an adsorbent for the removal of brilliant green (BG) dye from aqueous solutions. Comprehensive characterization using FTIR spectroscopy, XRD, TGA, FESEM, EDX, XPS and BET confirmed the successful synthesis of poly(AN-co-AMPS) with a high surface area of 64.07 m² g⁻¹. Adsorption studies revealed optimal removal conditions at pH 7, 298 K, 0.1 g adsorbent dosage, 7.5 mg L⁻¹ initial dye concentration, and 80 min contact time, achieving a maximum removal efficiency of 99.5%. Adsorption isotherm analysis demonstrated a strong fit to the Langmuir model with a maximum adsorption capacity of 16.28 mg g⁻¹, while kinetic studies indicated a pseudo-second-order mechanism. Thermodynamic analysis confirmed that the adsorption process is spontaneous (ΔG < 0) and endothermic (ΔH > 0). The primary adsorption mechanisms were identified as electrostatic, hydrogen bond and π–π interactions. Furthermore, regeneration studies showed that poly(AN-co-AMPS) maintained high stability and removal efficiency over six successive cycles. The Box–Behnken design (BBD) optimization provided a statistical model for predicting the adsorption performance under varying conditions. These findings highlight the potential of poly(AN-co-AMPS) as a promising, reusable adsorbent for BG dye removal from wastewater.