Electrodeposition Of Polymers And Metal Nanoparticles For Fabrication Of Electrochemical Sensors And Studies On Nanoelectrodes

Based on detailed reviews on polymer film modified electrodes and nanoscale materials,research was carried out for electrochemical sensor fabrications by surface modification of various substances involving niacinamide(VPP),PdCu alloy nanoparticles as well as phenosafranin(PS) and Pd nanocomposite.The fabrication of several novel nano-structured electrochemical interfaces by direct electrochemical deposition on GCE is reported.These sensors were used for electrochemical sensing of bioactive molecules including dopamine(DA),uric acid(UA),ascorbic acid(AA), and nitrite.In addition,we obtained nanoscale gold disk electrodes by electrochemical etching and probe into its electroanalytical application.The study is mainly focused on the following aspects:PdCu alloy nanoclusters were fabricated using electrochemical codeposition on the GCE.We found that the PdCu alloys were consisted of 15nm average sized nanoparticles.Most dispersed nanoparticles were elliptical,linked together but dispersed in a range like twigs and leaves.The fractal nanostructures may be referred to "2D-nanoclusters ".Some spherical clusters of 50-100 nm size,which consisted of closely assembled nanoparticles,can be found on the GCE like flowers.They were referred to "3D-nanoclusters".The 2D- nanoclusters can reduce the overpotentials of nitrite oxidation immediately and the 3D-clusters have weak ability to influence the overpotentials but strong ability to influence the current response.The reproducibility was excellen.Obviously,the PdCu/GCE had higher catalytic activity than singly Pd and Cu deposited electrodes,showing the synergic effect of the two metals in the nano-alloy.These findings indicated that catalytic activities may be related to the structure of nanoclusters.The complicity of the nanostructures may come from the easy variation of alloy compositions in result of several different crystalline structures. These results can be in favor of farther researching the correlations of alloy composition,nanostructures and catalytic activities.A chemically modified electrode has been prepared successfully by means of electropolymerization of niacinamide(VPP) at a glassy carbon electrode(poly-VPP /GCE).It was found that the polymer catalyzed the electrochemical oxidation of DA,UA,AA and NO₂^-,whose oxidation peak appeared at 0.163 V,0.291 V,0.034 V and 0.78 V(vs.SCE) respectively.Owing to the repulsion between the polymer film and AA,the poly-VPP/GCE has superior exclusive ability for AA.The co-existence of lots of AA did not interfere with the detection of DA or UA.It has been applied to the determination of NO₂^- with satisfactory results.The oxidation current was linearly related to nitrite concentration over wider range.The response was fast and had excellent reproducibility.The incorporation of Pd into PPS forms a nano-structured metal/polymer composite:PPS- Pd nano composite using cyclic voltammetry(CV).A Pd nanoparticle was formed during one cycle of CV scanning.Each Pd nanoparticle should be covered by a thin-layer of in-situ synthesized PPS film of nano-thickness. The Pd nanoparticles in the composite can be separated effectively and thus increased their effective surface area for the catalytic reaction.Moreover,the nano-Pd can coordinatively bind to PPS through N atoms lead to creat novel interface of Pd/PPS, which will change the properties of both Pd and PPS.The PPS-Pdcomposite modified layer can further reduce the overpotential and can significantly enhance the CV and DPV peak current response of nitrite oxidation in comparison with P.d and PPS individually modified layers.This can be attributed to the cooperative effect of PPS and Pd nanoparticles.Compared with the nitrite oxidation-based nitrite sensor reported previously,this method exhibits wider linear range and lower detecting limit.Lastly,nanoscale gold electrode was prepared by etching a fine Au wire,which was subsequently coated with electrophoretic paint deposited cathodically.The dimension of microelectrode could reach to 52 nm.And then,electrochemical activation is achieved by polarization at a fixed potential.It was found that the electrode catalyzed the electrochemical oxidation of nitrite.The DPV oxidation peak appeared at 0.75 V.The oxidation current was linearly related to nitrite concentration over the range 2～809μmol/L,with a detection limit of 0.3μmol/L.The response was fast and had excellent reproducibility.It could be found important applications in nitrite sensors.