Sulfurized biochar prepared by simplified technic with superior adsorption property towards aqueous Hg(II) and adsorption mechanisms

The biomass-based sulfurized biochar (CSS) that was prepared by co-heating sublimed sulfur and raw corn stalk in relatively low temperature (450 °C) and heating duration (15 min) showed an excellent adsorption property towards aqueous Hg(II) and was evaluated for its Hg(II) adsorption behavior and mechanism. Meanwhile, biochar-based sulfurized biochar (BCS) produced by co-heating sublimed sulfur and corn stalk biochar would be used for comparison. The results showed that the sulfur content of CSS and BCS was 7.4 and 2.2 wt% and the maximum Hg(II) adsorption capacity of CSS and BCS were 268.5 and 117.7 mg g−1. The Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy data suggested that the species of functional groups for Hg(II) adsorption on sulfurized biochar might be hydroxy, C=S and sulfoxide groups, etc. The X-ray photoelectron spectroscopy (XPS) results showed that the dominant existing forms of sulfur on sulfurized biochar were alkyl sulphides and sulphone groups along with thiophene and inorganic sulfur. The XPS data also verified the complexation between Hg(II) and CSS by forming irreversible Hg–S and Hg–O bond. Our research suggested that CSS processed more sulfur-containing groups with greater affinity to Hg(II) than BCS, and Hg(II) was stable adsorbed via complexation with hydroxy, C=S and sulfoxide groups in CSS by forming Hg–S and Hg–O bond.