Magnetic Biochar Decorated with ZnS Nanocrytals for Pb (II) Removal

Magnetic biochar/ZnS composites were successfully synthesized by deposition of ZnS nanocrystals (NCs) on magnetic biochar in a polyol solution. The as-prepared composites showed a high maximum adsorption capacity for Pb (II) up to 367.65 mg g–1, which was 10 times higher than that of reported magnetic biochar. Furthermore, the lead-laden magnetic biochar/ZnS composites can be easily separated from the solution by a magnet after adsorption because of the excellent superparamagnetic properties. The composites were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The adsorption process was well described by the pseudo-first-order model, and the adsorption isotherm could be well fitted by the Langmuir model. The thermodynamic studies showed that the removal of Pb (II) was an endothermic and spontaneous process. The present results warrant the promising application of magnetic biochar/ZnS composites in removal of Pb (II) from contaminated water.