Preparation, Characterization And Electrochemical Properties Of Novel Organic-inorganic Nanocomposites

Organophosphorus pesticides?OPs?are widely used in production of agricultural crops,vegetables and fruits because of their advantages of high insecticidal efficiency,low price,easy degradation and short half-life.However,excess organophosphorus pesticide residues has not only affected the export trade of agricultural products in our country,but also seriously destroyed the ecological environment and threatened the health of customers,which attracted people's high attention to.Therefore,it is necessary to develop a rapid,convenient,highly-efficient and practical method to detect pesticide residues in vegetables and fruits,which have become the focus of current research.Nanocomposite electrochemical sensors have become a powerful detection tool because they possess highly-sensitive sensing performances and can effectively detect pesticide residues.Based on this,multi-walled carbon nanotubes@titanium dioxides/carboxymethyl chitosan?MWCNTs@TiO₂/CMCS?and MWCNTs@gold graft poly?2-methacryloyloxyethyl ferrocenecarboxylate??MWCNTs@Au-g-PMAEFc?organic-inorganic nanocomposites were designed and synthesized,and used to modify electrochemical electrodes to detect organicphosphorus pesticide residues.The specific research content is as follows:1.Synthesis and characterization of MWCNTs@TiO₂/CMCS nanocomposites.First,MWCNTs@TiO₂ nanocomposites were prepared by in situ sol-gel method,and subsequently MWCNTs@TiO₂/CMCS nanocomposites were prepared by a non-covalent interaction between MWCNTs@TiO₂ and polymer CMCS.The chemical composition and crystal structure of MWCNTs,MWCNTs@TiO₂ and MWCNTs@TiO₂/CMCS nanocomposites were characterized by Fourier transform infrared spectroscopy?FT-IR?,Raman spectroscopy?Raman?,X-ray diffraction?XRD?,X-ray photoelectron spectroscopy?XPS?,ultraviolet-visible spectrophotometer?UV-vis?,field emission scanning electron microscopy?FESEM?and transmission electron microscope?TEM?.The experimental results showed that TiO₂ nanoparticles uniformly grew on the surface of MWCNTs,and MWCNTs@TiO₂/CMCS nanocomposites were constructed through a non-covalent interaction between MWCNTs@TiO₂ nanocomposites and CMCS,which has obviously improved the dispersion behavior of MWCNTs.2.Study on the electrochemical properties of modified glassy carbon electrodes based on MWCNTs@TiO₂/CMCS nanocomposites and the construction of electrochemical sensors.The effects of the system composition on the electrochemical behavior were investigated by cyclic voltammetry?CV?,and therefore the optimal composition and the best experimental conditions for the nanocomposites were obtained.Furthermore,the nanocomposite sensing films were used to detect the trichlorfon residues in vegetables and fruits.The results proved that the modified electrodes based on the nanocomposites had obvious redox currents and reversible electrochemical performances,which could be adjusted by changing the composition ratios of the nanocomposites.When the mass ratio of MWCNTs,TiO₂ and CMCS was 10:10:80,the nanocomposite electrochemical sensor had the optimal electrochemical performance.This sensor had not only good electrochemical sensitivity,reversibility and reproducibility,but also a wide linear range?1.0×10-5-1.0×10-11 mol L-1?and a detection limit as low as 4.0×10-7 mol L-1.Therefore,the nanocomposite electrochemical sensors have provided an accurate,rapid and reliable method for analysis of food safety.3.Synthesis and characterization of MWCNTs@Au-g-PMAEFc organic-inorganic nanocomposites.MWCNTs@Au nanocomposites were prepared by an in situ reduction technique,and then poly?2-methacryloyloxyethyl ferrocenecarboxylate??PMAEFc?was grafted onto the surface of MWCNTs@Au nanocomposites by ATRP to obtain a novel MWCNTs@Au-g-PMAEFc organic-inorganic nanocomposite.The structure and morphology of the products were characterized by 1H NMR,FT-IR,Raman,XRD,XPS,TGA,UV-vis,FESEM and TEM.The experimental results showed that Au nanoparticles were evenly coated on the surface of MWCNTs,and MWCNTs@Au-g-PMAEFc nanocomposites greatly improved the dispersion of MWCNTs.4.Construction of an electrochemical sensor based on MWCNTs@Au-g-PMAEFc modified glassy carbon electrodesThe influence of the compositional proportions and the grafting percentage of the composites on electrochemical properities was studied by CV,and the feasibility of the modified-electrode sensors was investigated by detecting trichlorfon residues in real samples.The experimental results showed that when the mass ratio of MWCNTs to Au nanoparticles was 1:4,and the grafting ratio was about 8.5%,the composite had good electrochemical performance:high sensitivity,good reversibility and reproducibility,low detection limit?6.7×10-9 mol L-1?and wide linear range?1.0×10-7?1.0×10-13 mol L-1?.Therefore,the construction of the electrochemical sensors based on the developed nanocomposites provides an effective way for trace analysis of trichlorfon pesticide residues in vegetables and fruits.