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Synthesis of Porphyrin Derivatives & Preparation, Characterization and Application of Porphyrin Self-assemblied Electrodes

Author: YuanHuiQing
Tutor: LuXiaoQuan
School: Northwest Normal University
Course: Analytical Chemistry
Keywords: Porphyrin Synthesis Self-assembled monolayers (SAMs) Electrochemical Impedance Spectroscopy (EIS) Electrocatalytic
CLC: O626
Type: Master's thesis
Year: 2008
Downloads: 19
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Abstract


Self-assembled monolayer （SAM） is an important embranchment of supramolecular chemistry, its emergence make the development of modern chemistry come to a new level. Well-ordered, directional, dense, intact self-assembled monolayer with controllable electrode surface microstructure can be designed on a molecule level. The self-assembled monolayer technique affords a convenient way of preparing unique distinct microstructure, which supply an important experiment plat for the complex surface studies.Porphyrins and their metal chelates are key ingredients in organism. Recently, they have been widely applied in catalysis, molecular recognition, photo-electron conversions, memorial material and medicinal fields. Porphyrins were studied in the field of self-assembly for their special properties. These researches showed better results than others SAMs constructed by other assembly molecules.On the basis of previous work in our workshop, porphyrin compounds with different structure were synthesized and charactered by spectroscopy in this paper. Combined with SAM technique, we focus our work on the studying of pinholes size and distribution on different alkyl chain length porphyrins modified gold electrode using Electrochemical Impedance Spectroscopy （EIS） method, which were helpful for further electrochemical investigation of electron transfer and corrosion at the interface. Furthermore, we also immobilized gold nanoparticles to the gold bulk electrode by self-assembled technology, the three-dimensional （3D） architectures modified electrode was fabricated and used for electrochemistry detection and electrocatalysis of dioxygen reduction in neutral aqueous media, results are good in our study.This paper is consisted with four paragraphs as follows:Chapter I: IntroductionIn this section, we summarized across-the-board the progress of the study of synthesis and actuality of porphyrins and metal-porphyrins, self-assembled technique, the characteristic of self-assembled monolayers, the the preparation and progress in application of of porphyrins SAMs.Chapter II: Study on synthesis and spectral properties of a series of porphyrins and metal-porphyrinsA series of hydroxyl-phenylporphyrins, thiol-derivatized-phenylporphyrins, nitro-phenylporphyrin, amino-phenyl-porphyrin and metal-porphyrins were synthesized by different methods, and the relation between the structure and property were also investigated by UV-Vis spectrum, fluorescence spectrum and 1H-NMR method.Chapter III: Preparation and character in the self-assembled thiol-porphyrin monolayers on gold electrodesSelf-assembled monolayers （SAMs） of thiol-porphyrins with different alkyl chain length （abbreviated as H2TPPO（CH2）nSH, n=3, 6, 9 and 12） on gold electrode have been studied by electrochemical impedance spectroscopy in electrolytes containing a one-electron redox couple. From the size and separation of pinholes on SAMs, both estimated the values of charge-transfer resistance and pore size model, we get the surface coverage （θ）. The results demonstrate that the surface coverage of saturated porphyrin modified gold electrode is close to unity （>99%）. But on the SAMs, a large number of pinholes still exist and acting as the microelectrodes, with average pinhole radius of 4-6μm and the separations are ten times greater than the pinhole size, of 40-70μm. Moreover, long chain length thiol-porphyrin SAM shows high surface coverage, larger pinhole size and excellent blocking of electron-transfer reactions between the redox mediator and the gold substrate. We demonstrated the large pinhole size is due to the aggregation of mass individual“micro-holes”.Chapter IV: Electroreduction of dioxygen based on the gold nanoparticle-assisted cobalt （II） porphyrin modified electrodeGold nanoparticles were immobilized to the gold bulk electrode by self-assembled technology, and the thiol-derivatized cobalt porphyrin （5-[p-（12-mercapto-dodecaoxy） -phenyl]-10,15,20-triphenylporphyrin cobalt （II） porphyrin, TDPPCo（II） ） monolayer was modified on the nanostructure surface using layer-by-layer （LBL） technique. The three-dimensional （3D） architectures modified electrode was fabricated using for electrochemistry detection and electrocatalysis of dioxygen reduction in neutral aqueous media. Results showed that the nano-based electrode exhibited excellent catalytic activity and high stability to dioxygen, a broad cyclic voltammogram reduction peak of dioxygen appears at around -173mV, which is 160 mV more negative than that at the bare polycrystalline Au electrode. The dioxygen was mainly reduced through four-electron process to H2O on the nano-based electrode.

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