Studies On The Preparation Of Carbon Nanotube/Polythiophene Composite-Modified Electrode And Its Application In Heavy Metal Ion Detection

New nanocomposite materials have the advantages of high conductivity,good chemical stability and structural stability.It would be of great significance for the detection of heavy metal ions by using the new nanocomposites for preparation of the modified electrodes with high performance.Combining the high electrical conductivity and good dispersibility of multi-walled carbon nanotubes（MWCNT）and poly（3,4-ethylenedioxythiophene）:polystyrenesulfonicacid（PEDOT:PSS）,MWCNT/conductive polymer composite material was prepared by chemical oxidation polymerization.The effects of MWCNT amount on the dispersibility,electrical conductivity and electrochemical performance of the composite were studied.In order to improve the adhesion property between the composite and electrode substrate,3-glycidoxypropyltrimethoxysilane（GOPS）was introduced.By changing the ratio of the composite and the GOPS,the paste with good adhesion and electrochemical performance was prepared for the modification of glassy carbon electrode,which was used to detect the heavy metal ions lead and cadmium by the stripping voltammetry.The main works as follows:1.Using 3,4-ethylenedioxythiophene（EDOT）as raw material,MWCNT and sodium polystyrene sulfonate（Na PSS）as dopants,MWCNT/poly（3,4-ethylenedioxythiophene）:polystyrenesulfonic acid（MWCNT/PEDOT:PSS）composite,was synthesized by in-situ chemical oxidation polymerization;Simultaneously,the effects of MWCNT amount on the dispersibility,conductivity,and modified electrode electrochemical performance of MWCNT/PEDOT:PSS composite were studied.The results showed that when the percentage of MWCNT in MWCNT/PEDOT:PSS composite was 0.03%,the dispersibility in aqueous solution,film conductivity and electrochemical performance of the MWCNT/PEDOT:PSS composite are obviously better than other experiment groups.Under the optimal conditions,the Zeta potential of MWCNT/PEDOT:PSS composite in aqueous solution and PBS buffer solution was-19.2 m V and-18.2 m V,respectively.The particle size of the composite was 525.8 nm and 532.3 nm,respectively.The film conductivity was 2.08 S cm^-1.The electrochemical redox process of potassium ferrocyanide probe on the MWCNT/PEDOT:PSS composite modified electrode was controlled by the diffusion.The oxidation/reduction peak current ratio of the potassium ferrocyanide probe at the MWCNT/PEDOT:PSS composite modified electrode was about 1.04 and the oxidation/reduction peak potential difference was 63m V.The stripping voltammetric response of the lead and cadmium ions at the MWCNT/PEDOT:PSS composite modified electrode was better than other experimental groups.2.The MWCNT/PEDOT:PSS composite modified electrode,PEDOT:PSS modified electrode,MWCNT modified electrode,GOPS modified electrode,PEDOT:PSS and MWCNT mechanically mixture modified electrode were characterized by cyclic voltammetry（CV）and electrochemical impedance spectroscopy（EIS）.The performances of the several kinds of electrodes for the detection of the lead and cadmium ions were compared by differential pulse anodic stripping voltammetric（DPASV）.Based on the MWCNT/PEDOT:PSS composite,the GOPS was added to improve the adhesion of MWCNT/PEDOT:PSS composite on the substrate.Simultaneously,the effect of GOPS amount on the electrochemical performance of MWCNT/PEDOT:PSS composite modified electrode was studied.The MWCNT/PEDOT:PSS/GOPS paste modified on the glassy carbon electrode,the amount of MWCNT/PEDOT:PSS composite and GOPS was optimized.The electrochemical performance of the MWCNT/PEDOT:PSS/GOPS paste modified electrode was characterized by CV and DPASV.The results showed that the electrode modified with the paste synthesized by adding0.04 g MWCNT/PEDOT:PSS composite and 4μL of GOPS into 900μL water had better adhesion and electrochemical performance and electrochemical response of the modified electrodes detected lead and cadmium ion was better.Under the optimal ratio,the oxidized/reduced peak current ratio of the potassium ferrocyanide probe at the MWCNT/PEDOT:PSS/GOPS paste modified electrode was about 1.06and the oxidation/reduction peak potential difference was 80 m V;The stripping voltammetric responses of the lead and cadmium ions at the MWCNT/PEDOT:PSS/GOPS paste modified electrode are the largest.3.Under optimal proportion of the MWCNT/PEDOT:PSS composite and GOPS,the volume of MWCNT/PEDOT:PSS/GOPS paste was optimized.The DPASV parameters including the deposition time,deposition potential,pulse width,pulse period and p H value were also optimized.The results showed that when the quality of MWCNT/PEDOT:PSS composite was 0.04 g,the volume of GOPS was 4μL,and the added water was 900μL,the formed paste was optimal to prepare modified electrode.2μL of the MWCNT/PEDOT:PSS/GOPS paste was drop-coated onto the surface of the glassy carbon electrode to prepare the modified electrode for the detection of the lead and cadmium ions by DPASV.The optimal DPASV parameters were as follows:deposition time,400 s;deposition potential,-1.1 V;pulse width,0.02 s;pulse period,0.1 s;and p H,4.0.The oxidation peak currents of lead and cadmium at the MWCNT/PEDOT:PSS/GOPS paste modified electrode was significantly better than other ratios.The linear range of lead ion detection was 0.1μg L^-1～100μg L^-1（R²=0.9941）.The detection limit was0.053μg L^-1,and the sensitivity was 0.0562μAμg^-1 L.The linear range of cadmium ion detection was 0.1μg L^-1～90μg L^-1（R²=0.9963）.The detection limit was 0.035μg L^-1,and the sensitivity was 0.0854μAμg^-1 L.In addition,the MWCNT/PEDOT:PSS/GOPS paste modified electrode showed good repeatability,reproducibility,stability,anti-interference and could also be applied to analysis of heavy metal ions in real samples.The recovery ratio of detection for the lead and cadmium ions in Xiangjiang River and tap water was from 93%to 112%and the relative standard deviation（RSD）was less than 6%.