Study On The Preparation Of Polymelamine/Carbon Composite Electrode Material And Its Application In Electroanalytical Chemistry

First of all,conductive polymers not only possess excellent processability of polymers,but also possess electrical and optical characteristics of metal and inorganic semiconductors.Their molecular structure design is flexible,and their excellent properties in electrical,optical and magnetic fields have attracted much attention.Polymelamine（pMel）is one of the new conductive polymers with electrochemical redox activity found in recent years.It has excellent processability of polymers and excellent conductivity of metals.On the other hand,carbon nanomaterials have large specific surface area and excellent optical and electrical properties,especially graphene is regarded as one of the most promising catalyst carrier as a new carbon material.Based on the excellent properties of the two kinds of materials,pMel/carbon composite electrode materials were prepared by electrochemical polymerization.This kind of electrode material has a broad application prospect in the fields of electroanalytical sensing and electrocatalysis.The main contents of this paper include the following aspects:（1）Electropolymerization of melamine was carried out on various carbon electrodes（including glassy carbon,graphene,carbon cloth and highly oriented pyrolytic graphite）.The polymerization effects on different substrates were compared and characterized by changing polymerization conditions（electrochemical parameters and polymerization methods,etc.）.A novel method was designed using solid state electropolymerization to prepare pMel thin film modified electrode.That is,a small amount of melamine solution was dropped and dried on the surface of the electrode,and then in a chloride-containing and monomer-free medium,the modified electrode of pMel film could be prepared quickly in one step.Graphene can significantly improve the polymerization and loading of Mel on the electrode and it is an excellent carrier for electropolymerization of Mel.Compared with pure pMel thin film modified electrode,the characteristic peak of pMel redox on composite electrode can be obviously enhanced.The chemically reduced oxide graphene（rGO）and Mel were modified onto the surface of glassy carbon electrode by drop coating method and solid state electropolymerization,and the rGO-pMel composite film modified electrode with good chemical properties was prepared.Further research on electrochemical application is based on the rGO-pMel composite electrode as prepared.（2）The electrochemical behavior of rGO-pMel composite film modified electrode in a series of buffer system was investigated by cyclic voltammetry.There is a pair of redox peaks related to pH,with good linear relationship between the oxidation peak potential and the pH value of buffer solution in the range of 1.93¹2.53.The correlation coefficient is 0.9931 and the slope is about 58 mV/pH.The rGO-pMel composite film modified electrode has been successfully applied to the determination of acidity of fruit juice and fruit living body.The performance of the electrode is stable and the measurement results have high repeatability,stability and accuracy.The modified electrode can be widely used for the direct determination of acidity of fruits and vegetables living body.（3）By utilizing the characteristic peak of reversible redox on the rGO-pMel composite film modified electrode,further determination of acidity of aqueous solution with high acidity can be achieved.The electrochemical response of the electrode was studied by cyclic voltammetry in the strong acid solution with the concentration of 0.1¹0.0 M.The results show that the peak potential of pMel oxidation and the concentration of the strong acid solution have a good linear relationship in the range of 0.1¹.2 M and 1.4¹0.0 M,respectively.The linear correlation equations were:E_pa（V）=0.0524c（H⁺）+0.5980,R²=0.9936;E_pa（V）=0.0187c（H⁺）+0.6420,R²=0.9904,respectively.Furthermore,the sample of simulated strong acid rare earth extract was studied,which had good selectivity and stability.The preparation method of the conductive polymer film modified electrode is simple and fast,and it can be widely used in the direct determination of acidity of high acidity aqueous solution.（4）The pH and free chlorine content of water are two important indexes of water quality monitoring.It was found that the rGO-pMel composite film modified electrode material had a strong electrochemical response to trace free chlorine.By optimizing the detection conditions,the electrode material was prepared in 0.1 M pH=5 phosphate buffer solution（PBS）.The linear range of the reduction current response is 0.05³0μM（R²=0.9933）.The detection limit is 5.3nM,.This composite electrode can be used for the determination of free chlorine in tap water with high sensitivity and selectivity.