The role and mechanism of K2CO3 and Fe3O4 in the preparation of magnetic peanut shell based activated carbon

Abstract

The impact of K2CO3 and Fe3O4 on the porosity development and the magnet evolution within magnetic peanut shell based activated carbon (MPSAC) was systematically studied. At the impregnation stage, K2CO3 was found to undergo one anionic hydrolysis. The formed KOH disrupted the key ester linkages between lignin and carbohydrates and removed a part of guaiacyl lignin. At the pre-carbonization stage, the introduction of K2CO3 greatly modified the carbonization behavior of peanut shell, shifting the weight loss peak from 350°C to 255°C. Meanwhile, a primary pore structure was developed, and some nanoscopic K2CO3 was detected. At the activation stage, a series of K-related species such as K2CO3·1.5H2O, K2CO3, K2O and K was formed, which was connected with the development of abundant micropores within MPSAC. Magnetic additive Fe3O4 functioned as an activation promoting agent while providing the Fe source. Above 500°C, the porosity structure increased the contact area between Fe3O4 and the reduction gases including CO and H2. Fe3O4 was reduced and successively converted into FeO and Fe with the increase of activation temperature. After that the Fe source was further converted into Fe3C.