Chemical Degradation of Mercury Alkyls Mediated by Copper Selenide Nanosheets

Methylation and demethylation of mercury compounds are two important competing processes that control the net production of highly toxic mercury alkyls, methylmercury (MeHg+ ) and dimethylmercury (Me2 Hg), in environment. Although the microbial and the photochemical methylation and demethylation processes are well studied in recent years but the chemical methylation and demethylation processes have not been studied well. Herein, we report for the first time that the CuSe nanosheet has remarkable ability to activate the highly inert Hg-C bonds of various MeHg+ and Me2 Hg compounds at room temperature (21 °C). It facilitates the conversion of MeHg+ into Me2 Hg in the absence of any proton donors. Whereas, in the presence of any proton source, it has unique ability to degrade MeHg+ into CH4 and inorganic mercury (Hg2+ ). Detailed studies revealed that the relatively fast Hg-C bond cleavage was observed in case of MeHgSPh or MeHgI in comparison to MeHgCl, indicating that the Hg-C bond in MeHgCl is relatively inert in nature. On the other hand, the Hg-C bond in Me2 Hg is considered to be exceedingly inert and, thus, difficult to cleave at room temperature. However, CuSe nanosheets showed unique ability to degrade Me2 Hg into CH4 and Hg2+ , via the formation of MeHg+ , under acidic conditions at room temperature. DFT calculations revealed that the Hg-C bond activation occurs through adsorption on the surface of (100)-faceted CuSe nanosheets.