Preparation of S-doped biochar with sodium thiosulfate as activator and sulfur source and its highly efficient adsorption for Hg2+

Sulfur-doped biochar (S₄BC) was prepared with cherry kernel powder as carbon source, Na₂S₂O₃ as sulfur source and chemical activator. Na₂S₂O₃ can activate biochar through the reaction with carbon, intercalation of alkali metals and the generated gas rushing out of pores, and at the same time, active sulfur atoms are doped into biochar during pyrolysis. The physical and chemical properties of S₄BC adsorbent were evaluated by various characterization techniques. The results show that S₄BC calcined at 800 °C has huge specific surface area of 959.6 m²/g, developed pore structure, and high content of S (18.84 wt%). Moreover, due to the existence of sulfur and oxygen functional groups, S₄BC-800 provides sufficient active sites for the adsorption of Hg²⁺. According to Langmuir model, the maximum adsorption capacity of S₄BC-800 for Hg²⁺ is 724 mg/g at 313 K, and the adsorption speed is fast with excellent stability and reusability. The microfiltration membrane device based on S₄BC-800 can effectively remove the low concentration of Hg²⁺ in the solution. In this study, a simple method for preparing SBC materials is developed, which is not only of great significance as an adsorbent for Hg²⁺, but also provides a new choice for the preparation of heteroatom-doped materials.