Preparation of magnetically separable mesoporous activated carbons from brown coal with Fe3O4

Abstract

Magnetically separable mesoporous activated carbon was prepared from brown coal in the presence of Fe3O4 as a bi-functional additive. Magnetic activated carbon (MAC) was characterized by low-temperature nitrogen adsorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and vibrating sample magnetometry (VSM). The evolution behaviors and transition mechanism of Fe3O4 during the preparation of MAC were investigated. The results show that prepared MAC with 6 wt% Fe3O4 addition having a specific surface area and mesopore ratio of 370 m2·g−1 and 55.7%, which meet the requirements of adsorption application and magnetic recovery. Highly dispersed iron-containing aggregates with the size of 0.1 μm in the MAC were observed. During the preparation of MAC, Fe3O4 could enhance the escape of volatiles during the carbonization. Fe3O4 could also accelerate burning off the carbon wall during activation, which leads to enlarging micropore size, then resulting in the generation of mesopore and macropore. As a result, a part of Fe3O4 converted into FeO, FeOOH, α-Fe, γ-Fe, Fe2SiO4 and compound of Aluminum-iron-silicon. The prepared activated carbon, which was magnetized by both of residual Fe3O4, reduced α-Fe and γ-Fe, can be easily separated from the original solution by external magnetic field.