Performance and mechanism of CuS-modified MWCNTs on mercury removal: Experimental and density functional theory study

A functional composite adsorbent of copper sulfide (CuS) loaded on the multi-walled carbon nanotubes (MWCNTs) was successfully synthesized and used for gaseous elemental mercury (Hg0) removal. The mercury removal performance and mechanism over CuS/MWCNTs was systematically studied based on a series of experimental characterizations and density functional theory calculations. The prepared CuS/MWCNTs showed excellent elemental mercury removal ability, and the best adsorption efficiency was achieved when the loading ratio was 10% and the reaction temperature was 70℃, with an average mercury removal efficiency of 85.8% in 2 h. SO2, NO, and H2O played an inhibitory role on the mercury removal over CuS/MWCNTs. Whereas, O2 had a certain promoting effect on Hg0 removal. The TPD desorption curves and XPS analysis results showed that the Hg0 in the flue gas was attached to the adsorbent surface in the form of HgS. Density functional theory analysis showed that Hg0 was physically adsorbed in the MWCNTs, which explains low Hg0 removal efficiency of pure MWCNTs. While the chemisorption mechanism dominated the strong Hg0 adsorption on CuS surface, accompanied by the formation of oxidized HgS, which was consistent with the experimental results. Combined with the macro and micro methods, this work provides an insight into the adsorption and oxidation mechanism of elemental mercury over the CuS/MWCNTs sorbent, which can guide further sorbent designs with targeted active sites and functional groups.