Light intensity Ferrioxalate

A ferrioxalate actinometer was used to determine the lamp light intensity (12). The quantum yield of loss (4>d) and of product formation ( p) were then calculated by standard methods (12). 

Wilkinson s catalyst. Irradiation at 366 nm of 0.001 M RhCPPh NO and 1 M cyclohexene in o-dichlorobenzene was carried out under 1 atm H2 at room temperature. The hydrogen uptake was monitored using a mercury manometer attached to the reaction flask. Hydrogen was added periodically in order to maintain 1 atm pressure in the system. The solvent and olefin were distilled twice and degassed by three freeze-pump-thaw cycles before use. A 1000 watt Hg lamp filtered with a glass filter to isolate the 366 nm Hg line was used for all photolysis experiments. The light intensity, measured by ferrioxalate actinometry, was 1.0 x 10 6 einsteins/min. 

Several authors have studied the effect of various parameters on the quantum yield of Fe(II) production (cPpeai ) from Fe(III)-oxalate complexes in the absence of oxygen. Parker [33] and Hatchard and Parker [32] found that ferrioxalate concentration, pH, light intensity and temperature did not significantly affect Fe(ii) at 366 nm. Abrahamson et al. [44] found, however, that Fe(ii) at 366 nm was approximately halved when the pH was increased from 2.7 to 4.0 or when a large excess of oxalate was added. At other wavelengths the solution pH and the presence of excess oxalate has a large effect on < pe(ii) (Table 2). 

A recent paper [84] presents a very complete study of the influence of different operational parameters on the FeOx process, such as light intensity, concentration of the reagents, and the presence of anions and HO scavengers. The case study was the herbicide 2,4-D. It was demonstrated that the system presented a higher efficiency than the photo-Fenton process, that the removal rate increased with fight intensity and that ferrioxalate concentration determined the fight absorption fraction, then controlling the removal rate. 

Light intensities were measured by potassium ferrioxalate actinometry (51). 

The exciting light was furnished by an irradiator composed of a 500-W xenon or 450-W high pressure mercury lamp as the light source and filters. The irradiation for the measurement of the quantum yields was performed with a JASCO CRM-FM spectroirradiator composed of a 2000-W xenon lamp as the light source and a grating monochromator. The light intensity was measured by potassium ferrioxalate actinometry [20], and the actinometric estimates were checked with an Eppley thermopile. 

The experiments were carried out in a glass-jacketed reactor vessel filled with 60 cm (or, in some cases 180 cm ) of reaction mixture and wrapped with aluminium foil. A 125-W immersion-type medium-pressure mercury lamp was applied as a radiation source. The light intensity was determined by ferrioxalate actinometry [20] (7a 1.5x10 mol photons dm" s" at 366 nm). A GBC UV-vis 911A spectrophotometer was used for the analysis. 

Absorption spectra were recorded using a GBC 911/A UV-vis spectrophotometer. For most of the continuous-wave experiments an AMKO LTl photolysis apparatus (containing a high-pressure 200-W Xe-Hg lamp and a monochromator) was applied. For irradiation of bromomercurate(II) complexes (2ir=253.7 nm), a low-pressure 16-W mercury-arc lamp was used. The light intensity was measured by ferrioxalate actinometry [15] and frequently checked by a thermopile. The experimental results were processed and evaluated by Quattro and Microsoft Excel programs on personal computers. The quantum yields for the formation of BrJ were determined from the initial rates of the photoinduced reactions, following the spectral changes. 

In order to provide a quantitative description of the product formation from the photolysis of PMPP, the quantum yield of biphenyl formation in methylene chloride was determined. Photolysis of PMPP in methylene chloride was therefore conducted with a medium-pressure mercury lamp using 254 nm band-pass filter. The light intensity was measured with ferrioxalate actinometry and the product yield was determined by gas chromatographic analysis of the samples photolyzed in methylene chloride. The quantum yield for biphenyl formation is ca. 5 x 10 . No change in the quantum yield for biphenyl was noticed in the presence and in absence of molecular oxygen. Since only a trace amounts of benzene and phenol were detected by gas chromatography, their formation quantum yields could not be determined accurately. 

The most accurate solution actinometer currently available is the potassium ferrioxalate actinometer. Potassium ferrioxalate solutions absorb light in the range 250-509 nm. This broad range is both an advantage and a disadvantage since the solutions are sensitive to room light and must be carefully shielded from light until the intensity determination is made ... 

The quantitative study of any photochemical process requires the measurement of the number of molecules that have formed or reacted and the number of photons absorbed. Chemical actinometers are commonly used for the determination of the intensity of the incident light on the sample or reaction vessel. Among these the ferrioxalate actinometer is probably the most accurate and widely used. Its useful range extends from 250 nm to 509 nm [17]. The uranyl oxalate actinometer, the Reinecke s salt actinometer, the benzophenone—benzhydrol actinometer and the o-nitrobenzaldehyde actinometer have also been used [4,18]. Obviously any photochemical reaction for which the quantum yield has been determined with reference to any known actinometer can itself be used as a standard. 

Polymers were deposited onto the quartz crystal (0.8 cm diameter) by casting from chloroform solution. The area coated with the polymer film was usually 0.13 cm2. The quartz crystal was placed in the middle of the sealed glass vessel which had a quartz window for UV irradiation. 2M KNO 3 aqueous solution was placed at the bottom of the vessel to control its humidity (RH=95%) at 25 "C. Irradiation of polymer films on the quartz crystal through the quartz window of the vessel was carried out with 254-nm light using a 5-W low-pressure Hg lamp (Toshiba LP-llB). The intensity of the incident light determined with a chemical actinometer (potassium ferrioxalate) (10) was 0.1 mJ/cm2 - sec at 254 nm. 

Figure 3.8 shows pe +] as a function of the irradiation time. The quantum yield for formation of iron(II) (that is the ratio of product formed to photons absorbed) when a 0.006 M solution of ferrioxalate is irradiated at 405 nm is 1.14 [10]. This allows us to calculate the intensity of light absorbed by the ferrioxalate solution, which is why this solution is called... 

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