Study On Double-template Molecularly Imprinted Electrochemical Sensors Based On Noble Metal-encapsulated ZIF-8 Heterostructures

Molecularly imprinted electrochemical sensors have high practical application value in environmental monitoring and food safety due to their high sensitivity and unique selective identification.However,most of conventional imprinting methods use a single substance as template molecules to prepare single-template molecularly imprinted polymer(MIP),which can only efficiently identify a single substance and cannot meet the needs of high-throughput detection.On the other hand,it is increasingly important to construct nanomaterials with high catalytic activity and adsorption capacity,and use them as the carriers to prepare MIP by surface molecular imprinting technology.Based on this,this paper intends to improve the conventional single-template MIP synthesis methods to prepare dual-template MIP,so as to achieve the purpose of simultaneous identification and detection of two analogues.In order to enhance the mechanical properties and the number of imprinted sites of MIP,ZIF-8 encapsulated noble metal heterostructures were doped or premodified on the electrode surface during the preparation process,and three highly selective and sensitive electrochemical sensing platforms were developed for simultaneous detection of different types of emerging environmental pollutants.The main contents are as follows:1.ZIF-8 nanoparticles were in-situ grown on the surface of Ag nanowires(AgNWs)via the coordination of Zn²⁺and 2-methylimidazole using AgNWs as carrier to construct a highly active and stable electrocatalyst AgNWs@ZIF-8 with unique necklace structure.The high electrical conductivity of AgNWs and the heterogeneous interface between Ag and ZIF-8 guaranteed the rapid electron transfer.The nanoscale structure of ZIF-8 and the exposed active site enhanced the catalytic activity of the material,which could realize the efficient electrocatalytic oxidation of two fungicides pyrimethanil and2-phenylphenol.In order to further improve the selectivity of the method,the double template MIP with specific recognition function was synthesized by sol-gel method using pyrimethanil and 2-phenylphenol as template molecules and AgNWs@ZIF-8 as doping materials.Thereafter,a molecularly imprinted electrochemical sensor was constructed for simultaneous detection of two fungicides using the AgNWs@ZIF-8@MIP as an electrode recognition element.Under the optimized conditions,the linear ranges of pyrimethanil and 2-phenylphenol are 0.80 nmol/L-50?mol/L and 0.50 nmol/L-50?mol/L,respectively,and the detection limits were 0.16 and0.27 nmol/L,respectively.When the sensor was applied to the determination of two fungicides in lake water,soil,millet,tea and green vegetables,the spiked recoveries were between 91.7 and 108%..2.Nanoporous Ag and its alloy are the research focus of nanomaterials,and their application prospect in electrochemical sensing field is wide.In this work,porous AgPtAg alloy microspheres with average grain size less than 280 nm were prepared and ZIF-8 was grown on the surface to obtain uniform core-shell structure.Compared with AgPtAg particles or ZIF-8 alone,AgPtAg@ZIF-8 showed enhanced electrocatalytic activity.Next,the double-template MIP was prepared using two hydroxylated polycyclic aromatic hydrocarbons 1-hydroxypyrene and 2-hydroxyanthraquinone as template molecules,methacrylic acid as monomer,ethylene glycol dimethacrylate as crosslinking agent,and azo diisobutyronitrile as initiator.An electrochemical sensing platform for the simultaneous identification and detection of 1-hydroxypyrene and2-hydroxyanthraquinone was prepared by modifying AgPtAg@ZIF-8 and MIP on the electrode surface,respectively.The linear ranges of the two hydroxylated polycyclic aromatic hydrocarbons were 0.050-50?mol/L and 0.0010-50?mol/L,respectively.The limits of detection were 1.28 and 0.83 nmol/L,respectively.Meanwhile,the sensor has excellent selectivity,reproducibility,and stability,providing a reliable way for the simultaneous detection of two hydroxylated polycyclic aromatic hydrocarbons in actual samples.3.Using multifunctional and highly adjustable compositions and structures,the construction of hollow structures will further confer higher performance and designability on metal-organic framework(MOF)materials.Compared with bulk MOFs,hollow MOFs have the characteristics of fast mass transfer speed,more active components,high exposure rate of active sites,and good compatibility.In this work,polystyrene microspheres were used as sacrificial template,and a layer of stable ZIF-8shell was grown after the modification of their surface with Pd nanoparticles.The hollow Pd@ZIF-8 compounds with high catalytic activity were obtained after etching the polystyrene cores.By virtue of the closed channel of ZIF-8 and the strong chemical interaction between ZIF-8 and Pd nanoparticles,Pd nanoparticles showed high dispersion and stability,and the obtained Pd@ZIF-8 has enhanced electrochemical activity.After the modification of this hybrid on electrode surface,the dual-template MIP synthesized with two amino-hydroxylated polycyclic aromatic hydrocarbons1-naphthylamine and 2-aminobiphenyl as template molecules and 1,2-bis(triethoxylsilane)ethane as functional monomer was further modified.The electrochemical sensor was constructed for simultaneous recognition and determination of 1-naphthylamine and 2-aminobiphenyl.Under the optimized conditions,the linear ranges of 1-naphthylamine and 2-aminobiphenyl on this sensor are 0.080-45?mol/L and 0.0050-45?mol/L,respectively,and the detection limits are 2.57 and 4.35 nmol/L,respectively.The sensor could be used for the efficient,rapid,and accurate detection of the two amino-hydroxylated polycyclic aromatic hydrocarbons in real samples.