Sensitive detection of Hg(II) on MoS2/NiS2 based on interfacial engineering to accelerate the Ni2+/Ni3+ cycle: Identification the role of atomic-level heterojunction-induced electron transfer in electroanalysis

The valence change of transition metal ions in nanomaterials can highly enhance the electrochemical detection performance toward heavy metal ions (HMIs), and how to further promote the valence change calls enormous concerns in electroanalysis. In this work, an interfacial engineering that combing the MoS₂ and NiS₂ together to form the MoS₂/NiS₂ complex is proposed. The density functional theory (DFT) results reveals that the novel atomic-level heterojunction between MoS₂ and NiS₂ will build an internal electric field (IEF), which leads to an enhanced conductivity and valence change behavior of Ni atoms in MoS₂/NiS₂ complex, resulting in a superior detection performance. In detail, the formation of atomic-level heterojunctions in the MoS₂/NiS₂ complex accelerates electron transfer due to the valence changes associated with Ni²⁺/Ni³⁺ cycling. The active Mo⁴⁺ species on MoS₂ act as electron donors, facilitating the reduction of Ni³⁺ to Ni²⁺ on NiS₂, thereby promoting Ni²⁺/Ni³⁺ cycling. As anticipated, the MoS₂/NiS₂ complex exhibits exceptional detection performance for Hg(II), with a sensitivity of 459.13 μA μM⁻¹ cm⁻², surpassing even that of other composite materials. In general, these findings are expected to significantly advance the application of electron transfer acceleration in electroanalysis based on the construction of heterojunction.