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

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 pHpzc 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.