Construction Of Electrochemical Sensors Based On COFs And Carbon Nanotubes For The Detection Of Pesticides

In the past few decades,pesticide residues have caused a series of problems such as environmental pollution,food safety and persistent health risks.Therefore,it is necessary to establish a highly sensitive detection methods for pesticide residues.Compared with gas chromatography,liquid chromatography and other conventional methods,electrochemical analysis method has the advantages of high sensitivity,good stability,simple operation and low cost.Covalent organic frameworks（COFs）,which have large specific surface area,good stability,designable pore channels and structures,have been successfully used for gas storage and separation,catalysis,battery and photoelectric sensors.While COFs has poor conductivity,in the application process,we can improve its conductivity by combining carbon materials which have good conductivity,so that COFs can be successfully applied in the electrochemical field.Therefore,in this paper,we have developed fast and sensitive pesticide electrochemical sensors based on covalent organic frameworks（COFs）and carbon nanotubes,which showed good performance in the detection of malathion and carbendazim.Firstly,an electrochemical acetylcholinesterase sensor based on a novel composite material COF@MWCNTs（MWCNTs:multi-walled carbon nanotubes）was fabricated for the detection of malathion.COF@MWCNTs was synthesized by a conventional solvothermal method,retaining the properties of COFs and MWCNTs.On the one hand,COF@MWCNTs was an ideal carrier for the immobilization of acetylcholinesterase because of its unique core-shell structure;on the other hand,the excellent electrochemical performance of MWCNTs made COFs successfully applied in the electrochemical field.Based on the inhibition principle of organophosphorus pesticides on acetylcholinesterase（ACh E）,differential pulse voltammetry（DPV）was used for the quantitative analyze of malathion.Under the optimal conditions,the linear range of the prepared sensor was 10^-9～10^-5 M,and the detection limit was0.5 n M.Besides,the sensor has good reproducibility,stability,anti-interference,and also has good recovery（96.0～105.0%）and accuracy（RSD<4.5%）in the detection process of tap water samples and spinach samples.Secondly,Co Cu nanoparticles were anchored on the surface of COF/SWCNTs（SWCNTs:single-walled carbon nanotubes）by Na BH₄ reduction method,which was synthesized at room temperature and the synthesized composite Co Cu/COF/SWCNTs was applied to construct an electrochemical sensor for the direct detection of carbendazim.The catalytic action of metal nanoparticles made the sensor show excellent performance in the electrochemical detection process.In addition,the interaction of bimetallic Co Cu nanoparticles and SWCNTs improved the conductivity of the composites,and COFs provided more reaction sites for the detection of carbendazim because of its good adsorption capacity.According to the redox activity of carbendazim,square wave voltammetry（SWV）was used for the detection of carbendazim.Under the optimal conditions,the linear range of the fabricated sensor was 0.001μM～10.0μM,and the detection limit was 0.65 n M.In addition,the sensor has the advantages of good reproducibility,high stability,and anti-interference.It also has good recovery and accuracy（96.1～102.1%,RSD<4.7%）in the detection process of tap water samples and pear samples.