UV-vis light

The combination of electrochemistry and photochemistry is a fonn of dual-activation process. Evidence for a photochemical effect in addition to an electrochemical one is nonnally seen m the fonn of photocurrent, which is extra current that flows in the presence of light [, 89 and 90]. In photoelectrochemistry, light is absorbed into the electrode (typically a semiconductor) and this can induce changes in the electrode s conduction properties, thus altering its electrochemical activity. Alternatively, the light is absorbed in solution by electroactive molecules or their reduced/oxidized products inducing photochemical reactions or modifications of the electrode reaction. In the latter case electrochemical cells (RDE or chaimel-flow cells) are constmcted to allow irradiation of the electrode area with UV/VIS light to excite species involved in electrochemical processes and thus promote fiirther reactions. 

The behaviour of phosphazene polymers upon irradiation with UV-vis light has been the object of several review articles during the last 20 years [408-413, 708] and for this reason it will be not treated in detail in this paper. The short summary of the topic presented here deals with the consideration that the photochemical behaviour of POPs originates in the combination of the transparency of the skeleton of these materials (up to well inside in the UV range of the... 

Most UV/VIS applications concern single-component quantification, which normally requires only relative measurements (e.g. the absorbance of an unknown concentration relative to the absorbance of a standard). Absorption and return to ground state are fast processes, and equilibrium is reached very quickly. Thus, absorption of UV/VIS light is quantitatively highly accurate. Method development involves selecting the wave-length(s) that yield the best results for the particular... 

Table 5.5 shows the main characteristics of UV spectrophotometry as applied to polymer/additive analysis. Growing interest in automatic sample processing looks upon spectrophotometry as a convenient detection technique due to the relatively low cost of the equipment and easy and cheap maintenance. The main advantage of UV/VIS spectroscopy is its extreme sensitivity, which permits typical absorption detection limits in solution of 10-5 M (conventional transmission) to 10 7 M (photoacoustic). The use of low concentrations of substrates gives relatively ideal solutions [20]. As UV/VIS spectra of analytes in solution show little fine structure, the technique is of relatively low diagnostic value on the other hand, it is one of the most widely used for quantitative analysis. Absorption of UV/VIS light is quantitatively highly accurate. The simple linear relationship between... 

Electronic Transition (resulting from absorption < of UV/VIS light) V4... 

Compare the energy transitions caused by infrared light absorption to those caused by UV-VIS light absorption. 

Li, H. Zhang, X. Cui, X. Lin, Y., Ti02 nanotubes/MWCNTs nanocomposite photocatalysts synthesis, characterization and photocatalytic hydrogen evolution under UV-vis light illumination./. Nanoscience andNanotechn. 2012,12 1806-1811. 

To elucidate the mechanism for the formation of Pt nanowires in the mesoporous chatmels we have made TEM and EXAFS observations of the H2PtCl,5/HMM-l (5wt% Pt) sample with methanol/water vapor under the exposure of UV-vis light by changing the irradiation time. Figure 15.1 la-e shows snap-shots of TEM images of the samples after irradiation for 4—48h [32, 34]. After 4h, small Pt... 

FAAS Flame atomic absorption spectroscopy the flame atomizes metals in solutions. Once in the gas phase, the atoms absorb UV-vis light, exciting electrons to higher energy levels. The amount of light absorbed is used to determine the metal concentration. 

In principle, absorption spectroscopy techniques can be used to characterize radicals. The key issues are the sensitivity of the method, the concentrations of radicals that are produced, and the molar absorptivities of the radicals. High-energy electron beams in pulse radiolysis and ultraviolet-visible (UV-vis) light from lasers can produce relatively high radical concentrations in the 1-10 x 10 M range, and UV-vis spectroscopy is possible with sensitive photomultipliers. A compilation of absorption spectra for radicals contains many examples. Infrared (IR) spectroscopy can be used for select cases, such as carbonyl-containing radicals, but it is less useful than UV-vis spectroscopy. Time-resolved absorption spectroscopy is used for direct kinetic smdies. Dynamic ESR spectroscopy also can be employed for kinetic studies, and this was the most important kinetic method available for reactions... 

Research Focus Preparation of superoxide anions generated using water-soluble fullerenes by irradiating with ultraviolet-visible (UV-Vis) light. 

Figure 3.14—Principle of the diode array detector. The flow cell is irradiated with a polychromatic UV/Vis light source. The light transmitted by the sample is dispersed by reflection on a grating and the reflected intensities are monitored by an array of photodiodes. Several hundred photodiodes can be used, each one monitoring the mean absorption of a narrow band of wavelengths (i.e. 1 nm).

The most widely used routine spectroscopic methods are those based on the absorp-tion/emission of UV-vis light. The UV-vis method is generally preferred over IR and NMR spectroscopy because (a) it is more sensitive, so more dilute solutions may be used, and (b) water and other common solvents present fewer problems with UV-vis than with IR and NMR methods. It is rare, but not impossible, that the light source used initiates some photochemical process, and this should be checked. 

Tian et al. have reported that bis(5-pyridyl-2-methylthien-3-yl)cyclopen-tene ligand 42 shows enhancement of photochromism by complexation with a Zn2+ ion [35]. They also found that the fluorescent properties, including the intensity and emission peak wavelengths of the compound, can be reversibly regulated by UV-vis light, Zn2+, and protons [36]. 

An example of recent achievement in this area is a flexible, thin film Cu(In,Ga)Se2 solar cell deposited on a titanium foil, which was combined with a TiC>2 photocatalyst layer and modified by a niobium-doped titanium oxide front electrode to function as a photoelectrochemical tandem cell/membrane for a direct light-driven hydrogen evolution from an aqueous solution [48], Under illumination with UV/vis light, the system produced up to 0.052 pLH2/scm2 (e.g. the hydrogen formation rate was approximately 7,250 pmol/h g relative to the amount of TiC>2 used). Several aspects of the operating principles of the photoelectrochemical devices, the materials requirements, main bottlenecks, and the various device concepts (in relation to H2... 

Because every phenol exhibits a higher or lower absorption in ultraviolet (UV) or UV-visible (UV-VIS) light, given the intrinsic existence of conjugated double and aromatic bonds, UV detection is the ideal method to localize a phenol in the effluent of a column. When a UV... 

Analysis is an integral part of research, clinical, and industrial laboratory methodology. The determination of the components of a substance or the sample in question can be qualitative, quantitative, or both. Techniques that are available to the analyst for such determinations are abundant. In absorption spectroscopy, the molecular absorption properties of the analyte are measured with laboratory instruments that function as detectors. Those that provide absorbance readings over the ultraviolet-visible (UV-vis) light spectrum are commonly used in high-performance liquid chromatography (HPLC). The above method is sufficiently sensitive for quantitative analysis and it has a broader application than other modes of detection. 

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