Novel insight into elemental mercury removal by cobalt sulfide anchored porous carbon: Phase-dependent interfacial activity and mechanisms

•Phase-dependent interfacial activity of cobalt sulfide to Hg0 has been elucidated.•CoS2 phase is more active in Hg0 oxidation than Co9S8 phase.•Co site on CoS2(111) surface represent the most active site to react with Hg0.•CoS2 anchored carbon contribute to an excellent material for gaseous Hg0 capture. Construction high-activity phase of metal sulfides on low-cost carbon represents a judicious way to develop advanced environmental materials, and yet the interrelation between crystal phase of metal sulfides on carbon matrix and interfacial reactivity of the composites towards gaseous elemental mercury (Hg0) has not been explored. Herein, we clarified the mechanisms of crystal phase in determining the Hg0 oxidation and adsorption activity of cobalt sulfide anchored carbon for the first time. Both CoS2 and Co9S8 phases were employed as model and synthesized on the same porous carbon matrix. The sulfur-rich phase of CoS2 anchored carbon has obvious advantages in providing Co3+ and S22- species comparison to Co9S8 anchored carbon, which act as reaction centers for Hg0. The CoS2 anchored carbon shows a high Hg0 adsorption capacity of 16.2 mg·g−1, which is superior to various activated carbons and metal sulfides. Surprisingly, the composite is able to utilize O2 and SO2 in flue gas to regenerate the consumed Co3+ sites, which is ascribed to the use of carbon as matrix. Both experimental and theoretical results confirm that Co sites represent the most active center for Hg0 adsorption. This work provides a new paradigm in design and engineering of high-performance materials in environmental remediation.