Platinum ions responsibility

In all of the studies summarized above, the Mebip ligands were covalently attached to a telechelic core and served either to chain-extend or cross-link these building blocks, in connection with various metal ions, into linear or cross-linked metallo-supramolecular polymers. Rowan et al. took a different approach when they blended complexes based on monofunctional dodecyl-Mebip and metal ions into methacrylate-based polymer matrices [85]. Interestingly, when complexes with platinum ions were used, a mechanically responsive material was obtained, which... 

All the six platinum-group metals are highly resistant to corrosion by most acids, alkalis, and other chemicals. Their high nobility is the main factor determining their chemical resistance, and the formation of. complex ions in solution is principally responsible for their dissolution under certain conditions. 

If the flow of oxygen falters, e.g. when the surface of the cathode is covered with water, then no gaseous 02 can reach the platinum outer layer. In response, firstly no electrons are consumed to yield oxide ions, and secondly the right-hand side of the cell floods with the excess protons that have traversed the polymer membrane and not yet reacted with O2-. Furthermore, without the reduction of oxygen, there is no redox couple at the cathode. The fuel cell ceases to operate, and can produce no more electrical energy. 

This theory has been successfully verified experimentally. Buck and Shepard [51] demonstrated that electrodes of the all-solid-state type have a response that is identical to that of similar electrodes of the second kind for response to halide ions and to a silver electrode for response to silver ions, depending on the degree of saturation with silver. This is achieved by soldering a silver contact to the membrane. If however the internal contact material is more noble than silver (platinum, graphite, mercury), the electrode with response to silver ions may attain a potential between the standard potential of a silver electrode g /Ag and the value... 

The existence of the nitryl ion in the presence of acidic substances suggested that nitrate ion in fused alkali nitrates might dissociate into N02+ and 0 2 ions (5). To determine the extent of the dissociation, it was necessary to develop an electrode potentiometrically responsive to either N02+ or 0 2. The only possibility for a reversible N02+ electrode that came to mind was nitrogen dioxide gas bubbling over platinum. This electrode did respond to N02+ in acidic solutions, but as ex-... 

It is the 4-coordinate square-planar geometry that makes Pt(II) complexes very different from those of most of the other metal ions familiar to the inorganic photochemist, including Cr(III), Ru(II), Os(II), Rh(III), Ir(III) (almost always 6-coordinate octahedral), copper(I) (4-coordinate tetrahedral), and lanthanides (8 or 9 coordinate). The square planar conformation is responsible for many of the key features that characterize the absorption, luminescence and other excited state properties of platinum(II) complexes. 

Cadogan et al. [73] deposited polypyrrole onto platinum from a variety of solutions and found the resultant films to be anion sensitive but very unselec-tive. When polypyrrole was deposited from NaN03 solution, however, the resultant electrode gave near-Nernstian responses to nitrate ion in the range 0.5-0.0005 M with selectivities of about 20 over other lipophilic ions such as iodide and perchlorate [74]. Similar electrodes could be fabricated via a screen-... 

Because any potentiometric electrode system ultimately must have a redox couple (or an ion-exchange process in the case of membrane electrodes) for a meaningful response, the most common form of potentiometric electrode systems involves oxidation-reduction processes. Hence, to monitor the activity of ferric ion [iron(III)], an excess of ferrous iron [iron(II)] is added such that the concentration of this species remains constant to give a direct Nemstian response for the activity of iron(III). For such redox couples the most common electrode system has been the platinum electrode. This tradition has come about primarily because of the historic belief that the platinum electrode is totally inert and involves only the pure metal as a surface. However, during the past decade it has become evident that platinum electrodes are not as inert as long believed and that their potentiometric response is frequently dependent on the history of the surface and the extent of its activation. The evidence is convincing that platinum electrodes, and in all probability all metal electrodes, are covered with an oxide film that changes its characteristics with time. Nonetheless, the platinum electrode continues to enjoy wide popularity as an inert indicator of redox reactions and of the activities of the ions involved in such reactions. 

A conductometric device for measurement of benzyltriphenylphosphonium ions was developed next [80]. Particles of benzyltriphenylphosphonium chloride-imprinted MAA-EDMA copolymer were held in a layer between two platinum wires using a filter paper. The device was exposed to the analyte in acetonitrile, an AC potential applied and the conductance recorded. The direct measurement principle is based on the enrichment of the analyte, a charged species, close to the electrode. A semi-linear response was observed between 1 mg/1 and 20 mg/1 (Fig. 18.4). In the two latter sensors it was anticipated that the effect of non-specific... 

The effect of individual reactants on the tetrahedral and cubic platinum nanoparticles was investigated in order to determine which reactants were responsible for the distortion of the nanoparticles [40]. There was significant dissolution of atoms from the comers and edges of both the tetrahedral and cubic platinum nanoparticles upon exposure to hexacyanoferrate (III) ions. Distorted tetrahedral and cubic platinum nanoparticles became the dominant shape (Fig. 18.3b and d, respectively). The distortion in shape of the nanoparticles was proposed to be due to the cyanide ligand of the hexacyanoferrate (III) ions adsorbing and reacting with the platinum comer and edge atoms of the nanoparticles to form Pt(CN) " complexes. 

Figure 18-6 shows how a hydrogen electrode is constructed. The metal conductor is a piece of platinum that has been coated, or platinized, with finely divided platinum (platinum black) to increase its specific surface area. This electrode is immersed in an aqueous acid solution of known, constant hydrogen ion activity. The solution is kept saturated with hydrogen by bubbling the gas at constant pressure over the surface of the electrode. The platinum does not take part in the electrochemical reaction and serves only as the site where electrons are transferred. The half-reaction responsible for the potential that develops at this electrode is... 

The specific conductance of a water sample provides a simple method to determine the total dissolved ionic solids present in the sample. It is also an inexpensive technique, which lends itself to continuous monitoring of a river or waste stream for the total ion content (Fig. 4.1), and can be easily used to check the accuracy of analyses conducted for specific ions. Specific conductance is measured via a pair of carefully spaced platinum electrodes, which are placed either directly in the stream to be measured or in a sample withdrawn from it [22]. The water temperature should be 25 °C, or the result corrected to this temperature. Voltages in the 12 to 14 range, and frequencies of 60 to 1000 Hz AC are used, plus a Wheatstone bridge circuit to obtain a conductivity reading in xmho/cm or xS/cm (microsiemen/cm). The response obtained is linear with the total ion content over a wide range of concentrations (Fig. 4.1). Examples of the conductance ranges and seasonal variation of some typical Canadian rivers are... 

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