Adsorbate iodine

A brown additive compound of iodine with the dibromo compound may separate during the titration this compound usually dissolves during the subsequent titration with thiosulphate, yielding a yellow solution so that the end point with starch may be found in the usual manner. Occasionally, the dark-coloured compound, which contains adsorbed iodine, may not dissolve readily and thus introduces an uncertainty in the end-point this difficulty may be avoided by adding 10 mL of carbon disulphide before introducing the potassium iodide solution. 

Documentation is carried out as soon as the iodine-colored chromatogram zones can be readily recognized. Then the adsorbed iodine can be allowed to evaporate in the fume cupboard or vacuum desiccator, so that the same chromatograms can be subjected to further reactions and separation steps (e. g. SRS techniques, 2-D separations, coupling techniques such as TLC/GC etc.). The chromatogram zones can also be stabilized by spraying with 0.5 to 1 percent starch solution [4, 5] the well-known blue clathrates that are formed (starch-iodine inclusion compounds) remain stable for months. 

The absorption in the visible region is assigned to the HOMO-LUMO transition of adsorbed iodine molecules. This band is shifted from the value of 540 nm, typical of iodine in gas-phase, to 490 nm, because of the interaction with the pore walls. 

Coordination of the iodo ligand onto the Ir, Pt and Au surfaces was accomplished by exposure of the clean electrode to 1 mM Nal for 180 seconds at the same pH at which subsequent experiments were to be performed. Unadsorbed iodide was rinsed away with supporting electrolyte. We determined the absolute surface coverage of iodine Tx (mole cm-2) by means of thin-layer coulometry in 1 M H2SO4 using two reactions attributable to the surface iodine, (i) Tj (mole cm-2) is obtainable from the charge for oxidation of adsorbed iodine to aqueous IO3-... 

TPSR experiments were carried out. Based on the products detected, propose a mechanism for the reaction(s) that take place on the surface. What is the main purpose of the XPS data reported in Figure 2 of the same article within the context of these studies Justify the assignments provided for the I 3d5/2 XPS peaks at 620.0 and 619.5 eV to molecular iodopropane and atomic adsorbed iodine, respectively. 

Bear46 as well as Katzbeck and Kerr47 established a solution to this problem. The authors observed that it is the so-called V-type (pregelatinized) starch that adsorbs iodine, whereas starch with the A- and B-crystallographic patterns is incapable of adsorbing iodine. The experiments of Rundle et al.48,49 appeared to be crucial in this respect and have shown that starch pretreated with 1-butanol adsorbs iodine vapor rapidly, even if the starch is thoroughly dried. In addition, if there is some inclusion of 1-... 

Huebner and Venkataraman69 demonstrated that starch can adsorb iodine from nonaqueous and not necessarily polar solvents, as shown in Table IV. Iodine adsorption by starch in aqueous ethanol increases as the ethanol content increases. Again, the solvent effect depends on the origin of the starch (Table II). The varying effects observed using benzene, ethanol, and chloroform may also be ascribed to the use of starches of different origin... 

A source of error is the adsorption of iodine by Cu(I) iodide. The adsorbed iodine imparts a buff color to the precipitate and interferes with the sharpness of the end point. In addition, the results may be low by as much as 0.3%, and fleeting end points may be observed. 

Foote and Vance suggested the addition of thiocyanate just before the end point. Cu(I) thiocyanate is less soluble than the iodide, and it is expected that at least the surface layers of the Cul will be transformed into CuSCN, which will have less tendency to adsorb iodine (as triiodide ion). Also, the last of the Cu(II) should produce the thiocyanate rather than the iodide of Cu(I), and the greater insolubility should bring about a more favorable equilibrium near the end point. Less interference from the formation of Cu(II) complexes should be experienced, owing to the more favorable equilibrium. The thiocyanate should not be added until most of the iodine has been reduced by thiosulfate, or appreciable reduction of iodine by thiocyanate may occur. ... 

Iodine adlayers can provide a protective layer against oxidation and contamination while single-crystal surfaces are handled in ambient atmospheres. Also, the adsorbed iodine can be replaced by CO, which in turn can be electrochemically oxidized in solution to yield a clean metal surface. Anodic dissolution of various metals occurs at step edges under carefully adjusted electrochemical conditions, and this is a promising method for in-situ preparation of atomically flat terraces. Such layer-by-layer dissolution has been demonstrated for Ni, Ag, Co, and iodine-modified Pd and Cu surfaces. 

The adsorption and structure of anions such as bromide, cyanide, sulfate/bisulfate, and iodide on metal electrodes have been extensively studied by in-situ STM in electrolyte solutions. Figure 41a displays a cyclic voltammogram for an Au(lll) electrode in 1-mM KI solution. The anodic/cathodic peaks below 0 V versus Ag/AgI are associated with adsorption/desorption of iodine at the surface. The smaller peaks at 0.5V are due to a phase transition in the adsorbed iodine layer, as can be observed by STM images taken at various electrode potentials. STM images shown in Figure 41b taken at a potential of —0.2 V show a periodic structure with perfect... 

A carbon black sample is treated with excess of iodine. The excess iodine is then titrated with a sodium thiosulfate solution. The result is expressed as adsorbed iodine per unit of mass of the sample. The iodine number depends on amount of volatiles, surface porosity, and extractables. The iodine number correlates with the nitrogen specific surface area. It is a simple method used to evaluate the quality of carbon black. 

The results at the most negative potentials can be interpreted in terms of a model where adsorbed iodine is converted to adsorbed iodide, which subsequently shows the behavior expected for a specifically adsorbed anion. That is, there is a marked dependence of the coverage on potential. 

The plateaulike features in the isotherm may be explained in thermodynamic terms. For example, we attribute the flatness in the region between —0.50 and — O.IOV to the absence of potential dependence of coverage of a neutral adsorbate (iodine). On the other hand, between —0.1 and +0.3V, further uptake involves adsorption of iodide. The potential... 

The liberated iodine is adsorbed by activated carbon, which is then separated from the brine and treated with sodium sulfite and sodium carbonate to re-form the iodide. The nonadsorbable iodide can be leached from the carbon in a concentrated form. Bierbaum45 found that better extraction can be secured through a modification of the final step. After the adsorbed iodine is converted to iodide, the carbon cake is dried and heated above 250° C to remove organic impurities. The iodides can thus be recovered in a purer form and less water is required for the extraction. Moreover, the heat treatment aids in regenerating the carbon for re-use. 

Ohman46 extracted the adsorbed iodine by an electrolytic process. The carbon containing the iodine is formed into a cake and made the cathode of an electrolytic cell. The adsorbed iodine is reduced to hydriodic acid which dissolves in the electrolyte and is oxidized to iodine at the anode. The iodine precipitates and settles to the bottom of the cell. 

This method is illustrated by the use of a solvent having solubilizing power for the adsorbed substance thus, adsorbed iodine is partially eluted with potassium iodide solution. This is a clear-cut example of elution through solubilizing action inasmuch as potassium iodide is not appreciably adsorbed. Many solvents have a dual function of both displacing and solubilizing an adsorbed substance. 

The STM result that dissolution of Pd atoms occurs selectively at step (disordered) sites provided the inqietus for an additional stuify which demonstrated that the I(ads)-catalyzed anodic dissolution process is able to regenerate an ordered Pd(l 11) surface from one that had been subjected to extensive Ar -ion bombardment [8]. This particular reordering reaction is unique because it occurs (i) in the absence of bulk conosive reagent, and (ii) only if a chemisorbed layer of iodine is present. This process may be viewed similarly to digital etching [9] under electrochemical conditions [10] except that (a) bulk material is not needed to replenish the adsorbed iodine that activates the surface, and (b) the dissolution process does not cease even after the atomically smooth surface has been regenerated. 

Figure 16.2.5 STM Images of Pt(lll) single crystal with a (Vs X VS) R30°-I adlattice (adsorbed iodine) imaged in O.IMHCIO4. (A) 12.5 nm X 12.5 nm area bias, 31 mV tunneling current, 25 nm (B) 2.5 nm X 2.5 nm image of boxed region in (A) (Q 2.5 nm X 2.5 nm image of the Pt(lll) substrate lattice [Reprinted with permission from S.-L. Yau, C. M. Vitus, and B. C. Schardt, J. Am. Chem. Soc., 112, 3677 (1990). Copyright 1990, American Chemical Society.]...

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