Hypersensitized electrochemical sensing of Hg(II) based on phase engineering of Co doped MoSe2 nanosheets: Insight in dynamic phase change induced by the chemical interaction between Se and Hg(II)

Transition metal dichalcogenides (TMDs) are regarded as promising nanomaterials for electrochemical detection to heavy metal ions due to their variable performance. However, their detection performances are still limited by inferior conductivities and adsorption ability. In this work, the defects and phase engineering strategy are proposed to utilize cobalt (Co) doped MoSe2 nanosheet for electrochemical detection of Hg ion (Hg(II)). Through Co doping, we successfully achieved the phase transition of MoSe2 from the 2H phase of semiconductor to the 1T phase of conductor. Moreover, the 1T MoSe2 is demonstrated to show a better adsorption and catalytic ability for Hg(II) detection than that of 2H MoSe2. As a result, the MoSe2 containing atomic ratio of Co is 10% (named CM10) owning suitable content of 1T phase has a superior sensitivity of 52.17 μA μM-1 and a low LOD of 3.96nM for Hg(II). More importantly, combining with the characterization of X-ray photoelectron spectroscopy (XPS) and density-functional theory (DFT) calculation, it is found that the Hg(II) adsorption will also lead to the phase change of MoSe2, and the change state in the samples after the adsorption of Hg(II) will be more accurate to be responsible for the improvement of catalytic ability.