Preparation And Electroanalysis Study Of UiO-67 Post-modified Metal Organic Frameworks Composite Electrode

Sodium nitrite?NaNO₂?is an inorganic salt which widely present in food and environmental systems,often used as a food preservative and fertilizer.However,sodium nitrite is hugely toxic.The human body takes the lethal dose in the range of8.7²8.3?M,and the interaction between sodium nitrite and amine can form carcinogens.Long-term intake can cause a series of symptoms and even cause cancer.Therefore,the detection and monitoring of sodium nitrite content are particularly important.Histamine?HA?is a biologically active nitrogen-containing organic substance that can participate in the body's local immune response and act as a neurotransmitter.However,histamine poisoning can cause various symptoms,such as dizziness,vomiting,diarrhea,dyspnea,and high blood pressure.Therefore,the monitoring of histamine content is also critical.In recent years,electrochemical detection has aroused many researchers'favor as a detection method due to their high sensitivity,simple operation,and low cost.However,the oxidation potential of nitrite on the traditional electrode is very high,which is not conducive to rapid and accurate detection.At present,electrochemical sensors for detecting histamine are mainly based on bio-enzyme electrodes.Due to the high price of bio-enzymes,challenging to fix,poor stability,and strict requirements on the detection environment,the practical application of enzyme-based electrodes is limited.Therefore,we need to develop new electrochemical sensors for the analysis of the above substances.Metal-organic frameworks?MOFs?are intrinsically extended porous solids formed by coordination bonding between organic ligands and metal ions or clusters.It has lots of advantages such as large specific surface area,high porosity,adjustable pore rules,and intriguing properties,so it is widely used in gas adsorption/separation,sensing,catalysis,and other fields.However,the application of MOFs as electrode modification materials in the field of electrochemical sensing is minimal.In order to reduce the oxidation potential of Sodium nitrite and accurately detect histamine,this thesis uses UiO-67-BPY crystal as a precursor.It obtains Cu@UiO-67-BPY material doped with copper through the post-modification method to improve the electrochemical activity of UiO-67-BPY and try to compound with graphene oxide?GO?to improve the conductivity of the material further,to achieve the electrochemical detection of histamine and sodium nitrite.Moreover,we also try to explain the detection mechanism from the performance of the electrode composite material and the structure-effect mechanism of electrochemical sensing,laying a preliminary theoretical foundation for the development of electrochemical sensors for specific analytes.The research contents of this paper are as follows:1.Synthesis and characterization of Cu@UiO-67-BPY/EGR/GCE composite materialsFirstly,we use the solvothermal method to construct UiO-67-BPY crystals through the self-assembly of zirconium chloride ZrCl₄ and2,2?-bipyridine-5,5?-dicarboxylic acid ligand?H₂BPYDC?.Then by reacting with copper acetate?Cu?OAc?₂?through the PSM synthesis strategy,copper-doped Cu@UiO-67-BPY was obtained,which significantly improved the electrochemical catalytic activity and material conductivity.The two materials before and after modification were characterized by PXRD,FT-IR,TGA,SEM,XPS,ICP,and other characterization methods.Finally,Cu@UiO-67-BPY was evenly dispersed in the suspension of graphene oxide.The Cu@UiO-67-BPY/GO/GCE modified electrode was prepared by the coating method,with a continuous CV scanning from-1.5 V to1.0 V,the GO was electrically reduced to electrically reduced graphene oxide?EGR?,which with higher conductivity.Finally,the Cu@UiO-67-BPY/EGR/GCE composite electrode was obtained.The electrocatalytic activity of the target electrode to potassium ferricyanide was explored by cyclic voltammetry.In order to compare the conductivity and electron transfer phenomena of different modified electrodes,includingbareGCE,EGR/GCE,Cu@UiO-67-BPY/GCEand Cu@UiO-67-BPY/EGR/GCE,we use the EIS method,and it proves that Cu@UIO-67-BPY and EGR,which in the composite materials,can form a synergistic enhancement effect on the electrochemical response of potassium ferricyanide,laying a theoretical foundation for the subsequent application of composite electrode.2.Cu@UiO-67-BPY/EGR/GCE electrochemical detection of sodium nitriteUsing the composite modified electrode material Cu@UiO-67-BPY/EGR/GCE as the working electrode,the electrochemical response to sodium nitrite was studied,and a composite electrochemical sensor of graphene oxide and Cu-doped MOF material was constructed.Because it has both the characteristics and functionality of MOFs and the high conductivity of graphene,it shows a good electrocatalytic effect on nitrite,which can significantly increase the oxidation peak current of sodium nitrite and reduce the oxidation potential.Subsequently,we studied the effects of the pH value of the electrolyte solution?PBS?and scanning rate?v?on the oxidation peak current(I_pa)and peak potential(E_pa)of sodium nitrite and the optimal reaction conditions were screened.Finally,the differential pulse voltammetry?DPV?was used to detect sodium nitrite in the solution quantitatively.The oxidation peak current and sodium nitrite concentration showed a good linear relationship between 10-6000?M:I_pa=-0.0062 C_NaNO2-7.2305?R²=0.998?,the detection limit?S/N=3?is as low as1.2?M.Besides,the modified electrode Cu@UiO-67-BPY/EGR/GCE has good stability,repeatability,and anti-interference performance in detecting sodium nitrite,and can be successfully used in the determination of nitrite in real samples.3.Cu@UiO-67-BPY/EGR/GCE electrochemical detection of histamineHistamine?HA?is a biologically endogenous active substance.As a kind of neurotransmitter,it is closely related to many physiological and pathological activities.The high-precision detection of histamine in organisms helps to explore various physiological and pathological mechanisms of the nervous system.In this chapter,we use Cu@UiO-67-BPY/EGR/GCE as the electrode to construct a new technology for high-sensitivity detection of histamine using an electrochemical immunoassay sensor.The electrical response signal of histamine on Cu@UiO-67-BPY/EGR/GCE electrode was studied by differential pulse voltammetry.In order to determine the optimal reaction conditions,we have explored the effect of the pH value of the electrolyte solution on the redox peak current intensity(I_pa)and peak potential(E_pa)of the substrate.In addition,differential pulse voltammetry was used to detect histamine specifically and with high sensitivity.The experimental results show that the linear range of the histamine detected by the electrochemical sensor is between 0-100?M,the equation is I_p=0.122C_HA+11.695?R²=0.998?,the detection limit?LOD?is as low as 0.595?M,and the sensitivity is 11.791 mA MM^-11 cm^-2?S/N=3?.Furthermore,Cu@UiO-67-BPY/EGR/GCE can be applied to the actual detection of human urine samples as well.Studies have shown that the electrochemical sensor constructed by the composite material has good detection stability and reproducibility for histamine,and has good selectivity and anti-interference,which resulted from synergistic effect.It is expected to develop into a new electrochemical sensor for rapid detection of histamine in vivo.