Electrochemical Analysis Mechanism Of Heavy Metal Ions Based On Special Physical Structure Of Iron-Based Nanomaterials

The design and fabrication of the electrochemical sensing interface is the ultimate goal of electroanalysis.For this purpose,the exploration of the interface response mechanism is the key to further design and optimize the sensing interface.In this paper,we explore the mechanism of the influence of the special physical structures of iron-based nanomaterials on the electrochemical detection of heavy metal pollutants,and thenestablish the structure-activity relationship between the two.Specifically include:（1）An iron-based nano-Fe/Mg/Ni ternary layered double hydroxide（Fe/Mg/NiLDH）with excellent adsorption properties was selected to construct an electrochemical sensing interface and used to the detection of Pb（Ⅱ）selectivity.It has been found that the coexisting interfering ions（Cd（Ⅱ）,Zn（Ⅱ）,Cu（Ⅱ）,Hg（Ⅱ））are mostly combined with dissociated hydroxyl groups（-O-）by non-specifically bound electrostatic interaction,while Pb（Ⅱ）is more to form MO-Pb（M=Fe,Mg,Ni）with a non-dissociated hydroxyl group by selecting a specific binding mode.Under the optimal conditions of detection,the undissociated hydroxyl groups on the surface of Fe/Mg/Ni-LDH nanomaterials are significantly more than the dissociated hydroxyl groups,which makes the selective adsorption of different heavy metal ions,leading to selective adsorption.As a result,the selective detection is finallyachieved.（2）The effects of different morphologies of Fe₂O₃（nanorods and hollow nanocubes）on the electrochemical detection of Pb（Ⅱ）were studied.The relationship between the electrochemical behaviors and the morphologies of Fe₂O₃ is investigated through the adsorption capacity and the adsorption sites.The results show that the electrochemical response of Fe₂O₃ nanorods toward Pb（Ⅱ）is much better than that of Fe₂O₃ hollow nanocubes.It is found that the e2O3 nanorods with（010）plane exposed more adsorption sites（Fe-O）on its crystal surface than the exposed（006）hollow nanocubes,and would lead to a higher response to Pb（Ⅱ）.The exposure allows the nanorods to adsorb more Pb（Ⅱ）for better electrochemical behavior.（3）A small-sized dumbbell-liked Au/Fe₃O₄（Fe₃O₄:10 nm）modified electrode was designed to achieve a highly sensitive electrochemical response to As（Ⅲ）.It is found that the Fe（Ⅱ）on the surface of the Au/Fe₃O₄ nanoparticles has very high activity.The As（Ⅲ）in the redox of the Fe（Ⅱ）/Fe（Ⅲ）cycle participates in the oxidation of As（Ⅲ）,enhancing the sensitivity.In addition,the X-ray absorption fine structure（EXAFS）technique was used to study the difference in the structure of two different sizes of Fe₃O₄（10 and 400 nm）.It was confirmed by experiments that the small size of Fe₃O₄ as a large number of defects.After the embedding of Au,the Au/Fe₃O₄ nanoparticles will further increase the disorder of Fe-0 and Fe-Fe bonds on the surface of Fe₃O₄.This structural defect and disorder have important significance for the improvement of Fe（Ⅱ）activity on the surface of small-sized Fe₃O₄.In this work,the Fe（Ⅱ）activity on the surface of Fe₃O₄ is used to enhance the electrochemical performance.The enhancement mechanism f the surface Fe（Ⅱ）/Fe（Ⅲ）cycle has a very good guiding significance to construct a unique sensing interface for the analysis of heavy metal ions.（4）Co_0.6Fe_2.4O₄ nanocubes（¹4 nm）with a high density surface defects are facile synthesized and then easily self-assembled on the surface of working electrode.The fabricated highlyhomogeneous sensing interface were successfully used to detect As（Ⅲ）with a considerable sensitivity.Owing to the exist of surface defects,Co_0.6Fe_2.4O₄ nanocubes exhibit high adsorption to As（Ⅲ）and the fast redox of As（Ⅲ）.The increased stripping current as the addition of Fe（Ⅱ）and Co（Ⅱ）suggests that the mediation effect of Fe（Ⅱ）/（Ⅲ）and Co（Ⅱ）/（Ⅲ）cycles on the surface of nanocubes are benefit for As（Ⅲ）analysis.Most importantly,this approach of tunable distribution of the nanosized defective nanoparticles on electrode provides a new opportunity for modifying electrodes without agglomeration and keeping the active of surface defects.（5）The preparation of Fe⁰@Fe₂MnO₄ nanotubes as realized by self-assembly method.The electrode process of FeoLbefore and after electrochemical redox reaction was compared with XPS.It was found that FeO acts as a strong reducing agent and surface electron-rich body.It can be used as an electron donor to provide electrons in the enrichment and reduction process of As（Ⅲ）.It can promote the enrichment and reduction of As（Ⅲ）on the electrode,and accelerate the surface of Fe（Ⅱ）/Fe（Ⅲ）.The loop has a positive effect.