Sulfur-anchored palm shell waste-based activated carbon for ultrahigh sorption of Hg(II) for in-situ groundwater treatment.

This study utilized a facile and scalable one-pot wet impregnation method for Hg(II) adsorption to prepare sulfur-anchored palm shell waste activated carbon powder (PSAC-S). The experimental results revealed that the sulfur precursors promote the surface charge on the PSAC and enhance Hg(II) removal via the Na2S > Na2S2O4 > CH3CSNH2 sequence. PSAC-S prepared using Na2S had significant Hg(II) sorption efficiencies, achieving a maximum sorption capacity of 136 mg g-1 from the Freundlich model. Compared to PSAC, PSAC-S had an enhancement in Hg(II) sorption behavior for heterogeneous interactions with sulfur. PSAC-S also demonstrated high Hg(II) sorption capacities over a wide range of solution pH, while ionic strength had an insignificant impact on Hg(II) removal efficiencies. Through various spectroscopic analyses, we identified the mechanisms of Hg(II) removal by PSAC-S as electrostatic interactions, Hg-Cl complexation, and precipitation as HgSO4. Moreover, PSAC-S unveiled high adsorption affinity and Hg(II) stability in actual groundwater (even in µg L-1 level). These overall results show the potentials of PSAC-S as an alternative, easily scalable material for in-situ Hg(II) remediation.