Mechanochemical preparation of well-structured copper sulfide for elemental mercury sequestration from coal combustion flue gas

Among various metal sulfides, copper sulfide (CuS) was found to be the most efficient one for the abatement of elemental mercury (Hg0) pollution in coal combustion flue gas because of the enrichment of under-coordinated sulfur along the 001 direction. Unlike saturated sulfur, the under-coordinated sulfur exhibits a dual role in oxidizing and immobilizing Hg0, but how to effectively synthesize (001) surface exposed CuS through a facile method has long been challenging in the Hg0 controlling community. In this work, a feasible synthesis strategy based on mechanical ball-milling procedure was proposed to synthesize (001) surface exposed CuS under mild conditions. Owing to the controllable nucleus formation and favorable crystalline growth manner under mechanochemical condition, the as-obtained CuS-based sorbent via ball-milling was primarily consisted of well -structured nanosheet containing abundant under-coordinated sulfur ligands, ensuring the adequate exposure of active sites. Consequently, the CuS as obtained exhibited the Hg0 adsorption capacity and uptake rate as high as 86.22 mg g-1 and 112.04 mu g g-1 min-1, far surpassing those benchmark metal sulfides as reported in previous studies. Notably, the Hg0 uptake rate of the CuS nanosheet surpasses that of CuS nanoparticle with irregular agglomeration by approximate ten folds. The under-coordinated sulfur, especially polysulfide (Sx2-), was demonstrated to be the primary ligand accounting for the oxidation and sequestration of Hg0 over the surface of CuS nanosheet. This facile synthesis logic with scale-up potential may also be applicable in the preparation of other metal sulfides in addition to CuS, marking an effective attempt stepping towards the industrial application of metal sulfides for Hg0 immobilization from coal combustion flue gas.