Chemically modified platinum surface

Carbonaceous substrates (graphite and glassy carbon) are generally preferred because of their mechanical, chemical, and electrochemical properties. Excellent results are also obtained by chemically modified platinum (154,156,179) and tin(IV) oxide electrodes (155). For example, glucose oxidase has been successfully immobilized by cross-linking the enzyme with BSA and GA onto an electrochemically oxidized platinum surface, with silanization using 3-amino-propyltriethoxysilane ... 

Chen et al. utUized a direct chemical reaction with a given solution (wet treatment) to modify the surface of the silicone rubber. The presence of a layer of PEO on a biomaterial surface is accompanied by reductions in protein adsorption, and cell and bacterial adhesion. In order to obtain a PEO layer on top of the silicone rabber surface, the surface was firstly modihed by incorporating an Si-H bond using (MeHSiO) , and followed by PEO grafting to the surface using a platinum-catalyzed hydrosilylation reaction. These PEO-modified surfaces were demonstrated by fibrinogen adsorption both from buffer and plasma, as well as albumin adsorption from buffer. Reductions in protein adsorption of as much as 90% were noted on these surfaces. 

Chemisorption [9] is an adsorptive interaction between a molecule and a surface in which electron density is shared by the adsorbed molecule and the surface. Electrochemical investigations of molecules that are chemisorbed to electrode surfaces have been conducted for at least three decades. Why is it, then, that the papers that are credited with starting the chemically modified electrode field (in 1973) describe chemisorption of olefinic substances on platinum electrodes [10,11] What is it about these papers that is different from the earlier work The answer to this question lies in the quote by Lane and Hubbard at the start of this chapter. Lane and Hubbard raised the possibility of using carefully designed adsorbate molecules to probe the fundamentals of electron-transfer reactions at electrode surfaces. It is this concept of specifically tailoring an electrode surface to achieve a particularly desired goal that distinguishes this work from the prior literature on chemisorption, and it is this concept that launched the chemically modified electrode field. 

Some papers have appeared that deal with the use of electrodes whose surfaces are modified with materials suitable for the catalytic reduction of halogenated organic compounds. Kerr and coworkers [408] employed a platinum electrode coated with poly-/7-nitrostyrene for the catalytic reduction of l,2-dibromo-l,2-diphenylethane. Catalytic reduction of 1,2-dibromo-l,2-diphenylethane, 1,2-dibromophenylethane, and 1,2-dibromopropane has been achieved with an electrode coated with covalently immobilized cobalt(II) or copper(II) tetraphenylporphyrin [409]. Carbon electrodes modified with /nc50-tetra(/7-aminophenyl)porphyrinatoiron(III) can be used for the catalytic reduction of benzyl bromide, triphenylmethyl bromide, and hexachloroethane when the surface-bound porphyrin is in the Fe(T) state [410]. Metal phthalocyanine-containing films on pyrolytic graphite have been utilized for the catalytic reduction of P anj -1,2-dibromocyclohexane and trichloroacetic acid [411], and copper and nickel phthalocyanines adsorbed onto carbon promote the catalytic reduction of 1,2-dibromobutane, n-<7/ 5-l,2-dibromocyclohexane, and trichloroacetic acid in bicontinuous microemulsions [412]. When carbon electrodes coated with anodically polymerized films of nickel(Il) salen are cathodically polarized to generate nickel(I) sites, it is possible to carry out the catalytic reduction of iodoethane and 2-iodopropane [29] and the reductive intramolecular cyclizations of 1,3-dibromopropane and of 1,4-dibromo- and 1,4-diiodobutane [413]. A volume edited by Murray [414] contains a valuable set of review chapters by experts in the field of chemically modified electrodes. 

The activity, stability, and tolerance of supported platinum-based anode and cathode electrocatalysts in PEM fuel cells clearly depend on a large number of parameters including particle-size distribution, morphology, composition, operating potential, and temperature. Combining what is known of the surface chemical reactivity of reactants, products, and intermediates at well-characterized surfaces with studies correlating electrochemical behavior of simple and modified platinum and platinum alloy surfaces can lead to a better understanding of the electrocatalysis. Steps, defects, and alloyed components clearly influence reactivity at both gas-solid and gas-liquid interfaces and will understandably influence the electrocatalytic activity. 

Carbon-supported catalysts, especially of platinum group metals, are used industrially in hundreds of reactions, particularly for manufacture of pharmaceuticals, perfumes, and plastics. Most carbon supports are manufactured by pyrolysis of carbonaceous materials such as wood, charcoal, coal, or organic polymers. Chemical pretreatment is used to modify the surface chemistry to impart superior catalytic properties. 

One other type of chemically modified electrode has been used in the study of cytochrome c, as described by Lewis and Wrighton. In this work platinum, gold, and p-type silicon substrates were modified with a polymeric overlayer which contained bipyridinium-type one-electron redox centers. These immobilized mediators transfer electrons between the electrode surface and diffusing ferricytochrome c at the potential of the mediators which is ca. 0.59 V more negative than the formal potential of cytochrome c. Oxidation of ferrocytochrome c is precluded because of the difference in the formal potentials of cytochrome c and the immobilized mediator. This same group has recently immobilized 2,3,4,5-tetramethyl-l-(dichlorosilylmethyl)-[2]-ferrocenophane on platinum. The juxtaposition of the formal potentials... 

The adhesion power of metal electrode to perfluorosulphonic polymer is used to modify the surface of a single electrode for the analysis of electrochemical reactions of special interest. Nafion -coated electrodes have been developed by Rubinstein Bard" . Various electron-conducting materials (glassy carbon, gold, platinum) are used as support for the Teflon layer. With these coated electrodes, the mechanisms of mass and charge transfer in the perfluorosulphonic material have been investigated and also the catalytic and photochemical properties of polymer doped with various chemical species . ... 

It is worth mentioning that a europium(III)-doped prussian blue analog (Eu-PB) film was modified chemically on the surface of a microdisk platinum working electrode to avoid the possible electrode fouling as well as to improve the ECL efficiency and detection sensitivity. After optimizing the conditions, the ECL intensity was in proportion to analyte concentration in the range from 0.01 to... 

Electrochemical oxidation of NO at the surfaces of novel electrode materials (e.g., platinum, gold, glassy carbon, carbon fiber) is known to be kinetically slow. However, accelerated electron-transfer kinetics of NO oxidation have been reported for a variety of chemically modified electrodes with polymeric metalloporphyrin films (11,12) and platinized Pt (13). These electrodes require less positive potentials for NO oxidation to nitrate ( 0.65-0.75 V vs. Ag/AgCl) and generate higher current (5-10 fold) than bare metal electrodes. 

Carbon supports typically undergo chemical or physical activation prior to platinum impregnation. The alteration of surface groups and functionalities on the carbon support can strongly influence the carbon-metal interaction that can directly affect the metal particle size, metal particle distribution, surface morphology of the carbon, and surface impurities that may be present. These parameters have been known to influence the catalytic metal stability and activity of the resulting catalyst. Common surface modifications strategies include chemical oxidation of the carhon or thermal activation to modify the surface structures. 

What one can consider as the first electrochemical sensor, i.e., a modified electrode surface dedicated to a specific target analyte, was a platinum electrode, covered by a protective membrane, the Clark electrode, for the determination of O2 in blood.The first biosensor was based on the determination with such Clark electrode of O2 depletion induced by glucose oxidase activity in the presence of glucose.These two examples show the importance of platinum as electrode material. It will be seen below that gold was also widely used for the development of chemically modified electrodes, especially due to the strong interaction with thiol-functionalized organic molecules allowing the formation of self-assembled monolayers (SAM). ... 

The effect of pH on heavy metal ion adsorption capacity was studied by previous researchers using the shake flask experiments. Eric and Roux used the shake flask experiment to study the influence of pH on the heavy metal ion binding onto a fimgus-derived bio-sorbent in the year, 1992. Also the evaluation of the effect of the hydrochloric acid concentration on the adsorption of platinum group metal ions onto chemically modified chitosan was done by Inoue et al., using the shake flask experiment [85]. Depending upon the type of P complexation with the surface such as monodentate, bidentate mononuclear, and bidentate binuclear the phosphorus desorption is potentially controlled. These complexes can be either non protonated or protonated depending on the suspension pH [184]. 

Catalytic processes frequently require more than a single chemical function, and these bifunctional or polyfunctional materials innst be prepared in away to assure effective communication among the various constitnents. For example, naphtha reforming requires both an acidic function for isomerization and alkylation and a hydrogenation function for aromati-zation and saturation. The acidic function is often a promoted porous metal oxide (e.g., alumina) with a noble metal (e.g., platinum) deposited on its surface to provide the hydrogenation sites. To avoid separation problems, it is not unusual to attach homogeneous catalysts and even enzymes to solid surfaces for use in flow reactors. Although this technique works well in some environmental catalytic systems, such attachment sometimes modifies the catalytic specifici-... 

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