Nitrogen-doped magnetic biochar made with K3[Fe(C2O4)3] to adsorb dyes: Experimental approach and density functional theory modeling

Magnetic biochar displays promising applications in dye wastewater treatment since it can be effectively separated by magnetism. However, the preparation of magnetic biochar with a large specific surface area is complicated and the effects of ferrous and/or ferric ions on dye adsorption are not clear enough. Herein, a facile one-pot approach of magnetic self-nitrogen-doped biochar fabrication was developed, using K3[Fe(C2O4)3] as an activator and iron supplier. Magnetic self-nitrogen-doped biochar could be easily separated with a magnet. Magnetic self-nitrogen-doped biochar had a large specific surface area (1034 m2/g) and excellent adsorption capacities for Congo red (1360 mg/g) and Rhodamine B (320 mg/g). From thermodynamics studies, Congo red adsorption on magnetic self-nitrogen-doped biochar is better than Rhodamine B. Based on the larger adsorption energies, magnetic self-nitrogen-doped biochar has a relatively stronger binding ability for Congo red than Rhodamine B, and the ferrous ions loaded on biochar surface are more beneficial for dye adsorption than ferric ones.