Reduction of Ions

Electroplating is the electrolytic deposition of a thin film of metal on an object. The object to be electroplated (either metal or graphite-coated plastic) constitutes the cathode, and the electrolyte is an aqueous solution of a salt of the plating metal. Metal is deposited on the cathode by reduction of ions in the electrolyte solution. These cations are supplied either by the added salt or from oxidation of the anode, which is made of the plating metal (Fig. 12.16). 

FIGURE 15.1 Polarization curves for the reduction of ions in 5X10 MNa2S20g + 0.009 M NaF solution at different metals. 

The addition of a cryptand to some polyelectrolytes leads to significant increases in conductivity and in some cases IR and Raman spectroscopy demonstrate that the cryptand breaks up the ion-ion interactions (Chen, Doan, Ganapathiappan, Ratner and Shriver, 1991 Doan, Ratner and Shriver, 1991). Apparently the reduction of ion association more than offsets the reduction in mobility of the cation-crypt complex, which has a larger effective radius than the simple cation. It is also possible that the cryptand-ion complex is rendered more mobile by the reduction of polymer-cation complex formation, but this point has not been investigated in any detail. 

Wagner-Traud Diagram, According to the mixed-potential theory, the overall reaction of the electroless deposition, [Eq. (8.2)] can be described electrochemically in terms of three current-potential i-E) curves, as shown schematically in Eigure 8.2. First, there are two current-potential curves for the partial reactions (solid curves) (1) ic =f(E), the current-potential curve for the reduction of ions, recorded from the rest potential E eq M the absence of the reducing agent Red (when the activity of is equal to 1, eq,M E m) and (2) = f(E), the current-potential... 

The ability to produce a deposit over a given surface, including recesses, is called covering power. As a point of practical importance, it may be noted that in some cases the required potential for deposition of the metal may not be reached in recesses and vias. Other processes, such as H2 evolution or reduction of ions such as Fe to Fe, may occur instead. In such cases, a preliminary strike deposit may be the answer. This is made by an extremely high current density for a very short time or in a specially formulated bath. 

Figure 1.8. Polarograra from a subsuale showing two polarographic waves. The wave at -1.8 V i.s due to reduction of ions in the supporting clccfiolyte.

Weaver, R., and Riley, R. J. (2006). Identification and reduction of ion suppression effects on pharmacokinetic parameters by polyethylene glycol 400. Rapid Commun. Mass Spectrom. 20 2559-2564. 

TheAPCImode may be preferable to E SI in terms of enhancing the sensitivity by reduction of ion suppression effects. 

The reduction of these precursors will produce multiatom particles and water vapor. This reduction process has a much smaller activation energy compared to the reduction of ion precursors, resulting in isolated atoms and protons. 

In the present work, this chemistry is studied for the "excessively ion-exchanged" Cu/ZSM-5, a catalyst of importance for NO abatement under 02-rich conditions [1,2]. In spite of the excellent results in this field, some questions have still remained open. For example, what is the role of molecular O2 in the promotion of the selective reduction of NO with hydrocarbons catalyzed by Cu/ZSM-5 [2]. Oxygen should play an important role in the redox chemistry of Cu/ZSM-5. The reduction of ion-exchanged Pt-Na/Y and the subsequent reoxidation by O2 results in PtO with no additional agglomeration, but which... 

Eor an ultimate proof of the electrochemical nature of the process, however, it has to be checked whether upon inversion of the pulse polarity also the opposite reaction of the hole formation, i.e., the reduction of ions from the solution, becomes... 

As in other electroless processes, chemical reduction of ions such as Fe2+, Cu2+, Ag+, Au+, Pd2+, and Pt4+ from their aqueous solutions is carried out using various reducing agents to produce different shapes of nanoparticles. Depending on metal, typical reducing agents involve borohydride, dimethyl amino borane, ascorbic acid, hydrazine, formaldehyde, etc. 

There are several important reasons to include sample preparation in modem liquid chromatography/tandem mass spectrometry (LC/MS/MS) methods. These include the elimination of matrix components from the sample reduction of ion suppression and, sometimes, improved sample utilization. 

Fig. 7.33 Electrochemical reduction of ions at a rotating n-GaAs electrode in 6 M HCL at different rotation velocities. (After ref. [35])...

If two or more electrochemical half-cell reactions can occur simultaneously at a metal surface, the metal acts as a mixed electrode and exhibits a potential relative to a reference electrode that is a function of the interaction of the several electrochemical reactions. If the metal can be considered inert, the interaction will be between species in the solution that can be oxidized by other species, which, in turn, will be reduced. For example, ferrous ions can be oxidized to ferric ions by dissolved oxygen and the oxygen reduced to water, the two processes occurring at different positions on the inert metal surface with electron transfer through the metal. If the metal is reactive, oxidation (corrosion) to convert metal to ions or reduction of ions in solution to the neutral metal introduces additional electrochemical reactions that contribute to the mixed electrode. 

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