Electrochemical Sensing Based On Porous Nanocomposites Derived From Covalent Organic Frameworks

Electrochemical sensor is a kind of sensor which converts the change of chemical quantity of detecting substance into electrical signal output based on the electrochemical property of detecting substance.It is generally understood that the choice of electrode modification material is critical to improving the performance of an electrochemical sensor.Among the many materials reported so far,the ideal material for changing electrodes is covalent-organic frameworks（COFs）,which feature a lot of heteroatoms and functional groups,a periodic structured pore structure,and a large specific surface area.In addition,considering that the performance of COFs is greatly reliant on their morphology,among various shapes,COFs with hollow nanostructures are favored due to their advantages of high specific surface area,good surface permeability,low density and high load capacity.Therefore,in this paper,hollow nanostructured COFs and their derived porous carbon materials were created using a template-assisted method.Based on these synthesized nanomaterials,electrochemical sensors were constructed for the detection of carbaryl,glucose and dihydroxybenzene isomers.The main works are as follows:（1）Pesticide electrochemical sensor based on HCOF_TFPB-DBD-Au NPs nanocomposites prepared by template method.The COF_TFPB-DBD shell rich in-SH was grown on the template of zeolitic imidazolate framework-8（ZIF-8）by the amine aldehyde condensation reaction between the two monomers.Then,after etching the template,the HCOF_TFPB-DBD with semi-hollow nanostructure was prepared,and the negatively charged Au NPs were anchored by S-Au bond.Finally,synthesized HCOF_TFPB-DBD-Au NPs was used to construct a highly sensitive electrochemical carbaryl biosensor.In the presence of acetylcholinesterase（ACh E）and acetylthiocholine chloride（ATCl）,the current response signal generated by[Fe（CN）₆]^3-/4-showed varying degrees of reduction with the continuous addition of carbaryl.The ACh E/HCOF_TFPB-DBD-Au NPs/GCE sensor exhibited good stability and reproducibility.The detection limit was 0.38μM,the linear range was 1.1μM-40μM,and the sensitivity was 0.00863 m AμM^-1 cm^-2.This work provides reference for the application of COFs in pesticide residue detection.（2）Enzyme-free electrochemical glucose sensor based on Ni/Ni O/NC nanocomposites derived from COF.The distinguished detection performance of enzyme-free glucose sensor makes it widely explored in accurate detection.Thus,a novel glucose sensing material based on template sacrifice method was constructed.Specifically,a covalent-organic framework(COF_BD)rich in O,N,O’-metal chelating sites was grown on the surface of Si O₂ template with different sizes and further coordinated with Ni²⁺.The target material of Ni/Ni O/NC was obtained by carbonizing the above material and removing the Si O₂ template inside.The characterization results showed that the material was a cellular carbon foam material with different cavity sizes rich in Ni/Ni O nanoparticles,which greatly magnified the detection sensitivity through the synergistic catalysis of Ni and Ni O and the screen of cavity size.Finally,the glassy carbon electrode（GCE）based sensor showed a low detection limit of 0.2μM,a wide detection range of 0.6μM-8.6 m M and a high sensitivity of 76.03μA m M^-1 cm^-2.Moreover,the paper based glucose sensor was also implemented utilizing target material and the results exhibited that the detection limit was 0.4μM,the linear range was 1.1μM-5.2 m M and the sensitivity was 42.38μA m M^-1 cm^-2,which also proved the excellent glucose detection performance of the target material.Further,the target material also showed outstanding practical application performance in the detection of glucose in real samples of juice and human serum by GCE based sensor and in sweat by wearable sensor.The sensor is of pioneering significance for providing a new material selection and adjustment methods for sensitive glucose sensor construction.（3）Electrochemical dihydroxybenzene isomers sensor based Pd/NC nanocomposites derived from COF.The cellular carbon foam material prepared by template sacrifice method have large surface area and abundant macroporous cavities.These advantages are very conducive to the enrichment of detection molecules and the rapid transfer of electrons and protons in the process of electrochemical sensing.Based on the inspiration of the previous work,the N,O-rich COF_TAPB-DA was coated on the surface of PMMA microspheres under the condition of normal temperature acidic aqueous solution.Because PMMA microspheres were easily soluble in organic solvents,the template molecules could be removed when Pd²⁺was complexed on COF_TAPB-DA in organic solvents.Finally,nitrogen-doped carbon material rich in uniform and dispersed Pd NPs and large pore cavities was prepared by calcination.In view of the excellent catalytic performance of the target material,Pd/NC/GCE electrochemical sensor was constructed for simultaneous detection of hydroquinone（HQ）and catechol（CC）.The detection limits of the sensor were 0.73 n M and 0.92 n M,the detection range were 2.2nm-38μM and 2.8 nm-38μM,and the sensitivity were 22.47μAμm^-1 cm^-2 and 21.48μAμm^-1 cm^-2.At the same time,the sensor had good selectivity,reproducibility and stability,and had a good application prospect for the detection of dihydroxybenzene isomers in real samples.