Electrochemical Sensitive Mechanism Of Transition Metal Doped Metal Oxides For Hg(Ⅱ)

Metal oxide is one of the most promising nanomaterials for electrochemical detection heavy metal ions on account of excellent redox activity.In general,the size and morphology of metal oxides are both crutial factors to affect their electrochemical detection performance.However,it has been found that excepting to obtained shape-controlled and highly stable metal oxides in recent years,it is also a promising method to improve the electrochemical detection performance of metal oxides by doping modification.For instance,typical transition metal doping can change the lattice structure of metal oxides and affect its physical and chemical characteristics（such as the exposure of active sites,conductivity and electronic structure）,ultimately achieving the regulation of its electrochemical detection performance.In this paper,metal oxides doped with different transition metals were prepared by simple hydrothermal and vapor thermal respectively.The influence of doping on the electrochemical detection heavy metal ions of metal oxides was systematically studied and the sensitive mechanism was explored.In the future,it provides experimental and theoretical support for improving the electrochemical detection performance of metal oxides based on doping.The specific research contents are as follows:1.A kind of porous Co₃O₄ nanosheets based on Ni doping strategy was synthesized by simple hydrothermal and subsequent annealing treatment（The atomic percentages of Ni source are 0 at%,2.5 at%,5 at%,7.5 at%and 10 at%,respectively.The obtained samples were named NC0,NC2.5,NC5,NC7.5 and NC10,respectively）.After Ni doping in Co₃O₄,the adsorption capacity and redox activity of Co₃O₄ were enhanced.However,electrochemical detection results show that the porous Co₃O₄ nanosheets doped with excessive Ni do not show better performance.After optimizing the dopant amount,NC5 showed the best electrochemical detection performance for Hg（II）,which with a sensitivity of 864.93μAμM^-1 cm^-2 and the limit of detection is 0.009μM.Through the in-depth study of the adsorption capacity and redox activity in the electrochemical detection process,it is proved that the redox activity promoted by valance state cycle is a key factor to affect the electrochemical detection performance,rather than the adsorption capacity of oxygen vacancies.It is shown that doping transition metals can regulate the valence state cycle of metal oxides to promote their redox activity and electrochemical detection performance.2.Spherical TiO₂ nanoparticles with Fe doped were prepared by one-step vapor thermal（The atomic percentages of Fe source are 0 at%,3 at%,5 at%,7 at%and 9 at%,respectively.The obtained samples were named FT0,FT3,FT5,FT7 and FT9,respectively）.Appropriate Fe doping in TiO₂（FT5）showed the best electrochemical detection performance for Hg（II）,which with a sensitivity of 400.63μAμM^-1 cm^-2 and the limit of detection is 0.11μM.The results indicate that Fe is successfully introduced into the lattice of TiO₂,occupying its tetrahedral position and activating TiO₂.The amount of oxygen vacancies and hydroxyl groups increased after Fe doping,which enhanced the adsorption capacity of TiO₂ toward Hg（II）.Although the amount of oxygen vacancies and hydroxyl groups in FT5 is not the largest,it possesses the optimal electrochemical detection performance.It can be attributed to more Fe²⁺/Fe³⁺and Ti³⁺/Ti⁴⁺cycles which involved in the redox of Hg（II）.This work further confirmed that redox activity is a crucial factor to affect the electrochemical detection performance.Moreover,transition metals with stronger intrinsic activity can activate the valence state cycle in insert metals oxides.