Oxidative stripping

In this section, we will present and discuss cyclic voltammetry and potential-step DBMS data on the electro-oxidation ( stripping ) of pre-adsorbed residues formed upon adsorption of formic acid, formaldehyde, and methanol, and compare these data with the oxidative stripping of a CO adlayer formed upon exposure of a Pt/ Vulcan catalyst to a CO-containing (either CO- or CO/Ar-saturated) electrolyte as reference. We will identify adsorbed species from the ratio of the mass spectrometric and faradaic stripping charge, determine the adsorbate coverage relative to a saturated CO adlayer, and discuss mass spectrometric and faradaic current transients after adsorption at 0.16 V and a subsequent potential step to 0.6 V. 

In order to develop more informative and direct method of studying the spillover effect of active particles, the authors of [37] suggested to use the sensor method of detecting migrating particles based on separation of sensor and emitter (donor) of active particles. The latter consists of small metal globules, or clusters (with a diameter of about 20-30 A) of Pt, Pd, Ni, etc. (activator) deposited on quartz or sapphire (AI2O3) plate in the form of a strip less than 1 cm wide. The sensor for detection of hydrogen atoms consisted of a zinc oxide strip (with a width of about 0.1 cm and thickness wlOO nm) deposited on the same plate at a distance of 0.03 or 0.6 cm (two versions) from the inner boundaries of activator strips [38]. 

The authors found that as CO is more strongly adsorbed than hydrogen, the introduction of CO into the electrochemical cell was immediately accompanied by its adsorption at the platinum electrode. This was shown by the decrease in the charge under the hydride udsorption features, and ulso the appearance of the oxidative stripping peaks 1 and II. 

Several groups have worked on the formation of ZnS using EC-ALE (Table 1) [29, 125, 130, 143, 154, 155, 159, 186], The first study was again by TLEC, where it proved difficult to quantify stripping coulometry for both Zn and S separately for deposits formed with over 5 cycles. Foresti et al. used a procedure where S was re-ductively stripped and Zn oxidatively stripped to accurately determine both Zn and S coverages from coulometry for deposits formed with greater numbers of cycles. 

FIG. 68. Schematic illustrating the electrochemical digital etching process on CdTe(lOO). A) initial surface, B) after oxidative stripping of a Cd atomic layer, C) after reductive stripping of the Te atomic layer. 

To learn that one of the most important areas of coulometry for the electroanalyst is stripping , in which analyte is allowed to accumulate on the surface of, e.g. a hanging mercury-drop electrode ( pre-concentration ), and then electro-oxidized ( stripped ). 

In a scheme complementary to the one just presented where thiols are removed by reductive desorption of thiols, molecules can also be removed during stripping of a UPD layer. This was demonstrated by Shimazu et al. [221] where an alkane thiol SAM was deposited onto a Au(l 11) that had been modified with Pb. Oxidative stripping of the lead also caused thiols to be removed. The empty sites were then subsequently filled with mercaptopropionic acid (MPA). A remarkable result is that the binary SAMs exhibit only one desorption peak. From this it was concluded that a well-mixed layer forms that is very different from the mixed SAM obtained by adsorption from solution containing both types of thiols. In this case the layer exhibits singlecomponent domains that are refiected by two desorption peaks. 

The sequence of the steps (stripping-oxidation-stripping-reduction), which was changed to reduction-stripping-oxidation-stripping The temperature of the ReDox cycles was increased to 804°C... 

Bond and coworkers [521] have described Au(III) electroreduction and Au(0) oxidation stripping processes in dilute aqua regia utilizing platinum, rhodium, iridium, gold, and glassy carbon electrodes. Sorption of tetrachloroaureate ions on carbon paste electrode modified with montmorillonite has been performed as a preconcentration step in the determination of gold in pharmaceutical preparation [522]. 

Figure 8.11 Electrochemistry of nanotubes solubilized by direct sodium reduction. Background of the supporting electrolyte solution is shown with dashed line. The star indicates the irreversible anodic peak due to the oxidative stripping of the reduced alkali metal film. 2 mM tetrabutylammonium hydroxide/DMSO working electrode Pt disk (r = 25 pm) data recorded at 298K scan rate 1 V/s. Potentials are referenced to SCE. Reproduced with permission from Ref. 122. Copyright 2008 American Chemical Society.

Design a process flow for the fabrication of an optical waveguide consisting of a doped oxide strip with square cross section embedded in and covered by an undoped oxide by using CMP. 

The bismuth/platinum system also has an advantage in model studies in the electrochemical environment because the modifier (bismuth) exhibits well-characterized oxidative stripping characteristics. Figure 8 shows the anodic stripping of... 

In the oxidation stripping process the uranium(VI) in the raw wet process acid is initially reduced to uranium(IV), which is extracted with a mixture of mono and dioctylphenyl esters of phosphoric acid in kerosene. Oxidation with sodium chlorate in phosphoric acid transfers the uranium to the aqueous phase and it is then extracted with trioctylphosphine oxide/di-(2-ethyIhexyl)-phosphate, as in the reduction stripping process. 

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