Regulation of nanostructure in coal-based activated carbon and its application for methylene blue removal

In accordance with an orthogonal experiment design, a series of ACs for methylene blue (MB) removal had been prepared in the presence of small amounts of KOH in raw material combined with delicate acid washing after carbonization and before steam activation. ACs were characterized, and their adsorption capacities for MB were determined as well. It was found that the content of element K in the char could be controlled by delicate acid washing. It was feasible to regulate and optimize pore structure in coal-based ACs by tuning preparation conditions concisely and properly, and the MB adsorption capacities were linearly correlated with their specific surface areas. Based on statistic analysis, it was revealed that among the four process variables studied for the sorbent prepared in this work, the activation temperature was found to be the most significant one for regulating the pore structure of ACs and resulted MB adsorption capacity, the next ones were the activation time, the flow rate of water vapor and the amount of KOH, and an optimized preparation condition was figured out. Furthermore, the pore size distribution of ACs intended to present a mesoporous nature when the flow rate of water vapor was 0.75mL/g/h and the amount of KOH was kept at 5%.