Sensitive detection of As(III) on Fe3O4/MoS2 through interfacial engineering to accelerate the Fe2+/Fe3+ cycle: Identifying the dominant role of electron transfer induced by valence change in synergistic electroanalysis

Fe-based metal oxide nanomaterials have attracted significant attention as the electroanalytical sensing for heavy metal ions (HMIs) detection. It is recently found that their activities should be mainly ascribed to their valance change behavior (i.e . the Fe 2+ /Fe 3+ cycle). However, how to promote the Fe 2+ /Fe 3+ cycle to further increase their detection performance is highly desired yet challenging. Herein, the nanocomposite of Fe 3 O 4 /MoS 2 is developed as a sensing for the electrochemical detection of the highly toxic As(III). Through a series of characterizations including the XPS and DFT, the Fe 3 O 4 /MoS 2 shows an accelerated electron transfer induced by the valence change of Fe 2+ /Fe 3+ cycle. The active Mo 4+ on MoS 2 can serve as electron doner to reduce the Fe 3+ to Fe 2+ on Fe 3 O 4 , and thus promotes the Fe 2+ /Fe 3+ cycle. Moreover, the synergistic effect between the excellent adsorption ability of Fe 3 O 4 towards As(III) and the good conductivity of MoS 2 will further benefit to the detection. As expected, the Fe 3 O 4 /MoS 2 reflects an outstanding detection performance to As(III) with a sensitivity of 4.16 μA•ppb –1 , which even much outperforms than that of noble-metal materials. Overall, these discoveries are expected to drive great advances in the application of the accelerated valence change behavior for electroanalysis. • Sub-10 nm Fe 3 O 4 is well dispersed on the surface of MoS 2 nanosheets. • Fe 3 O 4 /MoS 2 reflects a high detection sensitivity of 4.16 μA•ppb –1 to As(III). • XPS and DFT were applied to explore the underlying detection mechanism. • The active Mo 4+ of MoS 2 can serve as electron doner to promote the Fe 2+ /Fe 3+ cycle. • The inner electric field from Fe 3 O 4 to MoS 2 is established at their contact heterointerface.