Controllable Assembly Of Metal-Organic Framework And Noble Metal Nanocrystals And Research On The Novel Sensing Methods For Pesticide Residues

Excessive and unreasonable use of pesticides is widespread in modern agricultural production,resulting in the non-compliance of pesticide residues,which not only pollute water,soil,and environment,but also seriously endanger human health.Therefore,it is important to establish an efficient and simple analysis method for pesticide residue to ensure public safety.Electrochemical sensor is a kind of analytical technology that is sensitive,selective,simple,convenient,and able to realize real-time detection.The sensitivity and selectivity of electrochemical sensors can be significantly improved when nanomaterials or molecularly imprinted membranes are used as recognition elements.They can also considerably contribute to the detection and analysis of pesticide residues in complicated samples.In recent years,the composites of metal organic framework（Metal-Organic Frameworks,MOFs）supported metal nanoparticles combine the respective advantages of MOFs and nano-metal catalysts.They have high surface area,hierarchical pore structure,diverse topology structure,and abundant unsaturated metal sites,which have become an important direction in the study of MOFs and exhibited wide application prospect in sensing area owing to the significant synergistic effect.On the other hand,molecularly imprinted polymer（Molecularly Imprinted Polymer,MIP）is a kind of intelligent polymer material synthesized by molecular imprinting technology,which has selective adsorption and specific recognition for specific target molecules.The preparation method for MIP is simple,stable,and low cost.And the MIP can effectively improve the selectivity of electrochemical sensors and be used in harsh environment such as acid,alkali,high pressure,and high temperature.In this paper,several pesticides were selected as the analytes,and several novel molecularly imprinted electrochemical sensors with high imprinting efficiency and fast mass transfer rate were successfully fabricated via the introduction of noble metal nanoparticles doped MOF composite materials and new synthesis ideas for MIP.They can realize the high sensitive and selective detection of some pesticide residues.The main contents and results are as follows:1.Highly dispersed Au nanorods were successfully encapsulated inside zeolitic imidazolate framework ZIF-8（AuNRs@ZIF-8）by epitaxial growth or nucleus coalescence.The microporous ZIF-8 shell functions as a protective coating to effectively prevent AuNRs from dissolution,aggregation,and migration during the electrochemical testing,while it provides numerous channels for the mass transfer of reactants to the AuNRs surface.The as-synthesized AuNRs@ZIF-8 was then encapsulated in graphene oxide（GO）nanosheets to enhance the chemical resistance of the multicore-shell support,which possesses permanent porosity as well as high specific surface area and hydrophilicity.The excellent electrocatalytic performance of the resulting ternary AuNRs@ZIF-8@GO was demonstrated by sensing of niclosamide,dichlorophen,carbendazim,and diuron with high sensitivity,which outperformed the reported electrocatalysts for these four pesticides.This nanocomposite thus holds great promise as catalysts for electrochemical sensor fabrication in terms of abundant multiple active sites,enhanced catalytic activity,and remarkable stability.2.A disposable molecularly imprinted electrochemical sensor was developed towards highly sensitive and selective detection of organophosphorus insecticide phosalone（PAS）,employing home-made carbon paste microelectrode（CPME）modified with Zr-based metal-organic framework catalyst（Pt-UiO-66）and mesoporous structured conductive molecularly imprinted polymer（MIP）.Pt-UiO-66 octahedrons with isolated dispersed Pt nanoparticles active sites were firstly incorporated into the CPME to provide a remarkably amplified signal for voltammetric determination.Mesoporous MIP was then synthesized onto the Pt-UiO-66/CPME via electropolymerization and subsequent sol-gel process,which could bind the PAS template molecules through hydrogen bond,coordinate bonding,hydrophobic interaction,and?-?stacking interaction.Morphological,structural,and electrochemical characterizations revealed that this nano-sized MIP provided excellent features for PAS detection,including high porosity,large surface area,enhanced electron-transport ability,greatly improved diffusion capacity,and strong recognition specificity.Therefore,the resulting sensor exhibited outstanding linearly proportional concentration domain of 0.50nmol/L-20μmol/L,low detection limit of 0.078 nmol/L,marked selectivity over certain interferences with similar configurations,considerable repeatability,reproducibility,and stability for the analysis of PAS.Moreover,the sensor was successfully applied for determination of PAS in agricultural products and environmental samples with results in good compatibility with chromatographic method,indicative of the high reliability and practicability.3.Au@Pd core-shell nanocrystals were obtained by the regulation of experimental parameters with Au nanospheres as the seeds.After being introduced into the synthesis system of UiO-66,the Au@Pd@UiO-66 composite was prepared.In this composite,the Au@Pd is catalytic active site,the encapsulation of UiO-66 shell not only contributes to the stabilization of alloy particles and improves the cycling stability of the catalyst,but also accumulates the analyte.Moreover,2,4-dichlorophenoxyacetic acid（2,4-D）imprinted particles were synthesized using 2,4-D as the template,methacrylamide as the functional monomer,tetraethyl orthosilicate as the inorganic precursor,and vinyltrimethoxysilane as the coupling agent.The as-prepared Au@Pd@UiO-66 and MIP were sequentially modified on the glassy carbon electrode to construct a novel molecularly imprinted electrochemical sensor,which has a good specific recognition effect for 2,4-D.Based on the"gate effect"with ferrocyanide as the probe molecules,a linear range of 0.001-30μmol/L and a detection limit of 0.44 nmol/L were obtained for2,4-D detection.Additionally,the sensor showed excellent reproducibility and stability.4.The Cu₂O@HKST-1 core-shell structure was formed in situ after the reaction of dissociative Cu²⁺on the surface of sacrificial Cu₂O core and trimesic acid ligand in the solution.After adding HAuCl₄ into its solution as a precursor of novel metals,Au nanoparticles were formed and Cu₂O core removed by redox reaction between AuCl₄^-and Cu₂O,so the hollow Au-HKUST-1 catalyst was obtained at last,Both of the internal and external surfaces of this catalyst can be used as active sites for electrochemical reactions and can play the role of signal amplification.Thereafter,a molecularly imprinted electrochemical sensor of isoproturon was constructed with Au-HKUST-1 as the sensitizing matrix and the isoproturon imprinted sol-gel MIP as the recognition layer.The developed analytical method was applied to the detection of isoproturon in environmental samples and agricultural products,showing good sensitivity and selectivity.The linear range for detecting isoproturon is 1.0 nmol/L-45μmol/L,and the detection limit is 0.45 nmol/L.Compared with the reported methods for isoproturon detection,the sensor constructed in this work has better analytical performance.