The relationship of structure and organic matter adsorption characteristics by magnetic cattle manure biochar prepared at different pyrolysis temperatures

The preparation of magnetic biochar from cattle manure is an effective way for resource utilization. Fe3+- impregnated magnetic biochar for organic matter adsorption was synthesized by pyrolysis at 200, 400, and 600 degrees C respectively to investigate the influence of pyrolysis temperature on the structure and adsorption properties of magnetic biochar and their interrelationship. Congo red (CR) and Methylene blue (MB) were chosen to a representative of acidic and alkaline organics. The analyses showed that the number of functional groups decreased, and the specific surface area and iron oxides content increased with the increase of pyrolysis temperature. Fe3+ was loaded on biochar in form of gamma-Fe3O4 and converted into Fe3O4 when the pyrolysis temperature rose from 400 to 600 degrees C. As the pyrolysis temperature increased from 200 to 600 degrees C, the adsorption capacities of magnetic biochar to MB first decreased and then increased, whereas that to CR increased gradually. There are three main structural factors affecting the adsorption properties of magnetic biochar: surface area, functional groups, and iron oxides content. The adsorption of magnetic biochar to MB is mainly related to the competitive mechanism of surface area and functional groups. The main factor affecting the adsorption of MB by MCMB200 (magnetic biochar prepared at 200 degrees C) and MCMB600 (magnetic biochar prepared at 600 degrees C) is functional groups and surface area, respectively. The adsorption of CR by magnetic biochar is mainly related to the synergistic mechanism of surface area and iron oxides content.