Preparation Of Metal (Zn,Bi) Organic Framework Complexes And Electrochemical Detection Of Heavy Metal Ions

The rapid development of industrialization has brought about inescapable environmental problems,among which heavy metal pollution has caused serious harm to the environment and human body,and heavy metal ion detection has attracted widespread attention.At the same time,the trace detection of heavy metal ions can also diagnose or predict some diseases in human body.Therefore,it is important to develop a rapid,sensitive and low detection limit method for heavy metal ion detection.Traditional heavy metal detection methods mainly include spectrometry,mass spectrometry,UV-Vis spectrophotometry,etc.Each of these methods has its advantages,but there are problems such as high price of large detection instruments,difficulty in portability and operation.Electrochemical analysis is also an important means of metal ion detection,which is characterized by rapid analysis,low cost and simple operation,and has received wide attention in scholars.In this paper,starting from the structural design of electrode materials,we aim to develop novel electrode materials and construct an analytical platform for the rapid,trace and highly selective detection of heavy metal ions.Using metal-organic framework materials with different central metals as the main components,various methods such as ion exchange method and in situ growth method are adopted to prepare the ratiometric electrochemical sensing platform with Zn-MOF（ZIF-8）as the electrode material and the electrochemical sensor with CAU-17/biomass graphene（CSG）composite material with Bi-MOF（CAU-17）as the matrix material,respectively.The linear relationship between electrode materials and metal ion concentrations is successfully established through the rational adjustment of component content and reaction conditions to achieve the quantitative analysis of different metals(Pb²⁺,Cu²⁺,Zn²⁺,Cd²⁺).The main research of this paper is as follows:（1）Designing a dual-signal electrochemical sensing platform.Zn²⁺has a advantage that has a unique electrical signal,a metal-organic framework material（ZIF-8）with Zn²⁺as the central metal is selected as the electrode material to construct ZIF-8 into a proportional electrochemical sensing platform.Through the method of ion exchange,Zn²⁺in ZIF-8 is partially exchanged with the target metal ions(Pb²⁺and Cu²⁺),and ZIF-8-P and ZIF-8-C are obtained.Ions exchange between ZIF-8 and Pb²⁺or Cu²⁺is demonstrated with the help of XRD,SEM,XPS and other characterization means.We optimize the experimental condition by a series of electrochemical tests and perform the subsequent by differential pulse voltammetry（DPV）tests under optimum condition.It intuitively found during the DPV test that the redox peak(I_zn²⁺)current of Zn²⁺decreased significantly with increasing concentration of the target metal,while the oxidation peak currents(I_Pb²⁺and I_Cu²⁺)of the target metal increased significantly.The linear ranges of ZIF-8 for single metal ions(Pb²⁺and Cu²⁺)are 0.05-50 and 0.03-10μM,the detection limits corresponded to0.030 and 0.022μM and the sensitivity is 0.664 and 0.893μA/μM,respectively.This phenomenon is mainly due to the weak force between Zn-N bonds in ZIF-8,which can occur ion exchange with other cations.More importantly,Zn²⁺has a unique electrical signal and an easily distinguishable peak shape.I_zn²⁺is used as the reference signal,meanwhile,I_Pb²⁺and I_Cu²⁺are served as the detection signals to establish the relationship between signal ratio and concentration.Thus,realizing the electrical analysis of Pb²⁺and Cu²⁺.（2）The metal-organic framework（CAU-17）with Bi³⁺as the central metal is selected as the basis material,making full use of the characteristics of MOF with a large specific surface area and porosity.Meanwhile,the green biomass graphene is selected as the carbon material to improve the electrical conductivity of the electrode material.The Ni-doped biomass graphene is obtained by the nickel salt activation method for cellulose activation followed by high-temperature treatment at 900^oC,CSG is subsequently obtained by acid washing.CAU-17/CSG is synthesized by compounding CAU-17 with CSG through in situ growth,and the sheet CSG is successfully loaded uniformly on the surface of CAU-17.The best electroanalysis performance of CAU-17/CSG is achieved at the ratio of CSG addition of 500 mg（i.e.,CAU-17/CSG-5）.Optimizing the experimental conditions through a series of electrochemical tests,and conducting subsequent DPV tests under optimum conditions.The linear ranges of CAU-17/CSG for single metal ions(Zn²⁺,Cd²⁺,and Pb²⁺)are 1-16,0.03-3 and 0.05-3μM,respectively,and the detection limits corresponded to 0.059,0.012 and 0.012μM,respectively.Meanwhile,the linear ranges of the CAU-17/CSG for the simultaneous detection of Zn²⁺,Cd²⁺,and Pb²⁺are0.3-10,0.01-2,and 0.03-2μM,respectively,and the detection limits are 0.029,0.008,and 0.011μM,respectively.The excellent performance of the CAU-17/CSG-5modified electrode material is mainly attributed to the pore structure of CAU-17,the excellent conductivity of CSG and the good synergistic effect between CAU-17 and CSG.Therefore,the CAU-17/CSG-5 modified electrode still has good reproducibility and stability after 15 days.In addition,CAU-17/CSG shows good analytical performance in different real samples（water samples and blood samples）.