Dyes, adsorbed

Rotational dynamics of a fluorescent dye adsorbed at the interface provides useful information concerning the rigidity of the microenvironment of liquid-liquid interfaee in terms of the interfacial viscosity. The rotational relaxation time of the rhodamine B dye was studied by time-resolved total internal reflection fluorescent anisotropy. In-plane... 

With the D S SCs containing Hibiscus surattensis extract, the best performances were probably obtained because of the large amount of dye adsorbed on Ti02 (lxl cm2 active surface) in comparison with the other extracts from tropical flowers. Incident photon to current conversion efficiency (IPCE) values of 76% were calculated (2 — 590 nm). Jsc was 5.45 mAcm-2, Voc = 392mV, FF — 54%, and efficiency = 1.14%. Also, the stability of the photovoltaic devices was the best in the case of Hibiscus surattensis, even though it needs to be improved to achieve real long-term stability, especially as far as the sealing quality is concerned. 

Absorptive cathodic stripping voltammetry has been used [151,152] to determine nanomolar levels of nitrite in seawater. The nitrite is derivatised by diazotisation with sulfanilamide and coupled with 1-naphthylamine to form an azo dye. The dye adsorbs onto a mercury drop electrode and its reduction is fully reversible. The concentration of dye is linearly related to concentration of nitrite in the range 0.3-200 nM. Down to 0.3 nM nitrite can be determined in seawater for an adsorption time of 60 seconds. 

The protein binding capacity of immobilized dye adsorbents is also high and exceeds the binding capacity normally exhibited by natural biospecific adsorption ligands. 

We must first appreciate that a coloured species such as capsaicin has indeed adsorbed otherwise, there would be no layer to see. And a higher concentration of capsaicin yields a more intense colour as a straightforward manifestation of the Beer-Lambert law. We discern a relationship between the strength of the curry (by which we mean the concentration of the spices it contains) and the colour of the adsorbate, with a strong curry containing more spice and imparting a more intense colour. Conversely, the amount of dye adsorbed on the pan will be relatively slight after a mild curry (which is more dilute in the amounts of hot compounds it contains). 

Worked Example 10.1 The following data refer to the adsorption of the red-mauve dye from beetroot juice on porcelain at 25 °C. (1) Show that the data obey the Langmuir adsorption isotherm. (2) Demonstrate that 1.2 x 10 8 mol of dye adsorb to form a mono-layer. (3) Estimate the area of a single dye molecule if the radius of a plate was 17.8 cm (we assume the formation of a complete monolayer). 

Butterfly-type folding has also been discussed in the context of rhodamine dyes adsorbed on surfaces/53 In this case, too, nonexponential fluorescence decays are observed. A comparison of the consequences of the different reaction mechanisms with respect to free volume sensing is given in Section 5.4. 

Similar to what has been seen with CNT-doped electrodes, the presence of graphene resulted in enhanced charge transport and inhibited charge recombination. Additionally, as a consequence of doping rougher surfaces evolved, which, in turn, increased light scattering and amount of dye adsorbed onto the surface (Fig. 18.2). 

As it can be seen from Figme 17, adsorption process is not playing an important role in color and COD abatement from the solution. Similar results were foimd for catalyst C2, C3, C4 and C5. The exception was the original fly ash. Figure 18 shows a small amoimt of dye adsorbed on the original fly ash, see curve (b). 

The dye-clay composites were prepared by dispersing the clays in each solvent containing the dye at a quantity of 10-200% of the CEC. This experimental procedure led to almost complete intercalation at room temperature for 2-7 days. The composite was recovered by filtration and washing several times with each solvent for eliminating an excess of dye, and then dried in air. Assuming that the loss of dye adsorbed on the surface was fairly small upon washing, the net weight of dye intercalated was estimated from the residual dye concentration in a solvent measured by a colorimetric analysis. 

The photoactive component in these cells is a dye adsorbed chemically onto the surface of the semi-conductor. When light hits this surface, the dye (S) absorbs a photon and becomes excited (S ) in this state it transfers an electron into the TiOj semi-conductor (injection). The positively charged dye (S+) then passes its positive charge to a redox mediator in the bulk electrolyte. The oxidised mediator is attracted to the counter electrode where it is reduced back by electron transfer, thus completing the circuit. 

Li et al. have performed a comparative study on the surface-enhanced resonance hyper-Raman scattering and surface-enhanced resonance Raman scattering (SERRS) of dyes adsorbed on Ag electrode and Ag colloid [210]. 

It is unlikely in such cases where different species exist on the surface that the photocurrent spectrum coincides with the absorption spectrum, since the efficiency of charge transfer will be different for different species. Memming 52> has concluded that for a cyanine dye adsorbed on a SnO 2-electrode the monomer seems to be more effective for charge injection than the dimer or higher aggregates. Hauffe and co-worker S3> have found that chelating dyes are especially efficient for sensitized electron injection into ZnO-electrodes which is seen in the variation of the photocurrent spectrum. 

Stability tests performed in sandwich-type cells containing the dyes adsorbed on Sn02/Sb electrodes demonstrated a high stability, with optical density changes lower than 2% after cycling the electrochromic device 20000 times between -0.5 and +0.5 V. 

Similar behavior is observed in the potential-dependent luminescence of a ruthenium dye adsorbed to 2 [52]. Although the flat-band potential of 2 is known to shift positive in the presence of the potential-determining Li+ ion, relative to the TBA+ ion [5,68], this effect cannot explain the observed behavior. For example, in our experiments, the dye injects in both cases, but it takes a much smaller negative potential excursion to turn off the injection process in the presence of Li+ than with TBA+ [52]. This is the opposite of what would be expected if only equilibrium (i.e., dark) band edge motion were responsible for the effect. 

On the other hand, oxide semiconductor materials such as ZnO and 2 have good stabilities under irradiation in solution. However, such stable oxide semiconductors cannot absorb visible light because of their wide band-gap character. Sensitization of wide-band-gap oxide semiconductor materials by photosensitizers, such as organic dyes which can absorb visible light, has been extensively studied in relation to the development of photography technology since the middle of the nineteenth century. In the sensitization process, dyes adsorbed onto the semiconductor surface absorb visible light and excited electrons of dyes are injected into the conduction band of the semiconductor. Dye-sensitized oxide semiconductor photoelectrodes have been used for PECs. 

We considered the concentration-dependent spectral data of Figure 4A to be a manifestation of the adsorption equilibrium of the dye. Specifically, we assumed that the initial linear increase of /-absorbance represents binding of all the added dye at the substrate and that departure from this linear portion corresponds to added but unadsorbed dye the latter would then account for the sudden increase of the M/J absorbance ratio. It follows from this interpretation that the intercepts obtained by extrapolating the linear sections of the plot of dye concentration vs. J. or M/J absorbance, should correspond to the amount of dye adsorbed at saturation of the surface. If we assume further that the absorbances of Figure 3 and 4A obey Beer s law, then the intensity of the /-band will be... 

In comparison with an azo dye adsorbed on anhydrous barium sulfate (31), the K/S values of Figure 5 are remarkably large. In part this is because of the high extinction coefficient of the Pseudocyanine s /-band (cf., Figure 1) and in part to the non-zero base line in Figure 5A. It was experimentally convenient to use an 0.2 absorbance filter in the sample beam of the spectrophotometer in the absence of this filter—it had no influence on the final results—the K/S value at saturation coverage would... 

Figure 8A. Adsorption isotherms of Pseudocyanine (No. 1, Circles) and of Astraphloxin (No. 2, Squares) in AgBr (Dispersion D) containing 0.2% gelatin at 23°C., pBr 3, pH 6.5. The data are expressed as the concentration of free dye (c) in equilibrium with dye adsorbed per mole of AgBr (a). Open data points and solid lines Results calculated from surface spectra. Solid data points and dashed lines Results obtained from phase-separation procedure B. Adsorption isotherms of Figure 8A expressed in terms of the Langmuir equation. See text...

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