Adsorption characteristics of aqueous Cr(VI) by using magnetic γFe2O3/Fe3O4 lotus stem biochar by NaOH modification

The article aims to investigate the adsorption characteristics of aqueous Cr(VI) biochar by magnetic γFe2O3/Fe3O4/NaOH lotus stem biochar (SMBC) which was synthesized with modification of γFe2O3, Fe3O4, and sodium hydroxide. Biochar samples before and after adsorption were characterized with Brunauer Emmett Teller, X-ray diffractometer, Fourier transform infrared spectroscopy, X-ray photoelectron spectrometer, magnetism. The results showed that SMBC was successfully prepared with the saturation magnetization of 66.608 emu/g and the BET specific surface area of 239.56 m2/g. The adsorption isotherm study showed that the theoretical maximum adsorption capacity of SMBC for Cr(VI) was 196.270 mg/g. The process of its adsorption of Cr(VI) fit the Langmuir isotherm adsorption model and the pseudo-second-order kinetic model, indicating that this process was chemical adsorption. The adsorption mechanism of SMBC to Cr(VI) mainly included electrostatic interaction, redox, and complexation. Desorption and regeneration experiment results showed that SMBC after adsorption could be easily recycled from the solution under the force of an external magnetic field. Furthermore, the adsorption capacity of SMBC reached about 80% of the original even after six desorption/regeneration cycles. This study proves that SMBC showed great potential as a separable and reproducible adsorbent to remove Cr(VI) in wastewater with excellent adsorption performance, strong adaptability, environmental friendliness, and good recycle.