Electrochemical Sensor Based On Ultrathin Layered Double Hydroxide Snanosheet Composite Membrane And Its Application In Detecting Organophosphorus Pesticides

Organophosphorus pesticides have become the most widely used insecticides because of their low price,convenient synthesis,and high activity in inhibiting pests and diseases.Due to irrational application of organophosphorus pesticides, organophosphorus pesticide residues can be found in the atmosphere,soil, groundwater.In order to prevent organophosphorus pesticides from causing potential harm to organisms,there is an increasing need to design sensitive and effective methods to analyze organophosphorus pesticides of food and drinking water in daily life.At present,electrochemical sensors have been widely used in pesticide detection due to their advantages of simple operation,low cost and fast detection speed.As we all know,ultrathin two-dimensional nanomaterials are widely used to construct electrochemical sensors due to their unique structure and properties,but they also have some shortcomings.For example,ultra-thin nanomaterials have the characteristics of easy stacking of nanosheets,and stacking causes some catalytic sites of the nanomaterials to be masked.In this paper,three kinds of nanocomposites were designed and prepared based on CoAl layered double hydroxides,which effectively hindered the stacking of layered double hydroxides.It was applied to the construction of electrochemical sensor to realize the rapid detection of organophosphorus pesticides.The main research contents and results of this paper are as follows:(1)CoAl-LDH-P was successfully prepared by adding structure modifier poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)triblock copolymer(P123)into the preparation system of CoAl layered double hydroxides.Then,ultra thin porous CoAl layered double hydroxides nanosheets(CoAl-LDH-P)were prepared by ion exchange method and solvent stripping method.Structural characterization showed that CoAl-ELDH-P had a typical hexagonal structure,and many nanopores appeared on the surface.Nanopores could effectively improve the electron transfer rate,increase the specific surface area of CoAl-ELDH-P,and release more catalytic sites.The glassy carbon electrode(GCE)was modified by CoAl-ELDH-P.the peak current of electrochemical reduction of fenitrothion and Triazophos at the modified electrode CoAl-ELDH-P/GCE was much higher than that of coaleldh modified electrode without pore,and the difference of reduction peak potential between the two electrodes was 307 m V.Under the optimum conditions,differential pulse voltammetry(DPV)was used for the simultaneous determination of fenitrothion and Triazophos.The peak currents of fenitrothion and Triazophos showed a good linear relationship in the concentration range of 0.01?M to 100?M.the detection limits of the two pesticides were 4 n M and 3.6 n M,respectively.In addition,the CoAl-ELDH-P sensor has excellent antiinterference ability,and it has been successfully applied to the detection of practical samples.(2)CoAl-ELDH-P@Au nanocomposite was prepared by in-situ reduction of gold nanoparticles by Na BH₄ on CoAl-ELDH-P surface.The structure characterization showed that Au nanoparticles were successfully loaded on the CoAl-ELDH-Pnanosheets,and the size of Au nanoparticles was about 6 nm.The addition of gold nanoparticles can effectively improve the electrical conductivity of Coal-ELDH-P,so CoAl-ELDH-P@Au nanocomposites show large specific surface area,excellent electrical properties and mass transfer rate.An electrochemical sensing platform based on CoAl-LDH-P@Au nanocomposite was used to detect Fenitrothion,and the reduction mechanism of Fenitrothion on CoAl-ELDH-P@Au/GCE was investigated by cyclic voltammetry(CV).The results show that the reduction of Fenitrothion on CoAl-ELDH-P@Au/GCE is a four-electron transfer process,and the linear range of Fenitrothion detection is 0.01?M to 100?M,and the low detection limit is 3.2 n M.CoAl-ELDH-P@Au/GCE has excellent anti-interference properties and a good recovery rate in the range of 92.5%-111%in actual sample tests.(3)Firstly,the Al atom layer of the precursor of MAX phase(Ti₃Al C₂)was selectively etched in the mixed solution of Li F and HCl to obtain MXene and then uses the co-precipitation method to load CoAl-LDH nanosheets on the surface of MXene (Ti₃C₂T_x)to prepare the MXene/CoAl-LDH nanocomposites.The structural characterization showed that CoAl-LDH was uniformly loaded on the single-layer MXene nanosheets.MXene/CoAl-LDH was modified on the glassy carbon electrode to construct a new electrochemical sensing platform for the detection of Fenitrothion.The results showed that the electrochemical performance of MXene/CoAl-LDH was significantly better than that of MXene and CoAl-LDH.The specificity of MXene/CoAl-LDH for the detection of fenitrothion was studied by CV and DPV.It was found that the phosphate group in fenitrothion could form a chelation with the Ti defect site in mxene and adsorb on the surface of the electrode to achieve a enrichment effect.The specific detection of Fenitrothion was realized.In addition,the sensor has a linear detection range of 0.01?M-120?M,a detection limit of 3.7 n M,and good anti-interference capability.