Fabrication of cotton textile waste-based magnetic activated carbon using FeCl3 activation by the Box–Behnken design: optimization and characteristics

Abstract

Cotton textile waste-based magnetic activated carbon was prepared via simultaneous activation-pyrolysis using FeCl₃ as a novel activating agent. The response surface methodology based on the Box–Behnken design method was applied to optimize the preparation parameters and predict the specific surface area of the samples. The optimal activated carbon was obtained at a mass ratio of FeCl₃/CTW, activation time and activation temperature of 1.62 : 1, 1 h and 700 °C, respectively. The experimental maximum yield and iodine adsorptive value (32.66% and 714.55 mg g⁻¹) of the resultant carbon were close to that of the predicated response values (34.85% and 783.75 mg g⁻¹), respectively. SEM, N₂ adsorption–desorption isotherms, XRD, PPMS, FTIR and pH_pzc measurements were conducted to analyze the physicochemical characteristics of the optimal sample. The results showed that the carbon matrix had a high specific surface area of 837.39 m² g⁻¹ with abundant micropores and acidic surface functional groups, and the saturation magnetization (Ms) was 5.2 emu g⁻¹ due to the formation of Fe₃O₄. The maximum adsorption of Cr(VI) by the carbon reached 212.77 mg g⁻¹. Furthermore, the addition of FeCl₃ lowered the pyrolytic carbonization temperature and inhibited the generation of volatiles in the activation-pyrolysis process. Meanwhile, the formation of Fe₂O₃ and Fe₃O₄ derived from FeCl₃ was beneficial for the development of vast micropores.