Potassium ferrioxalate

Aqueous solutions of this salt are the most reliable and practical actinometer for UV and visible light up to 500 nm, first proposed by Hatehard and Parker in 1956 [8]. Under light excitation the potassium ferrioxalate decomposes according to the following equations  

The quantity of Fe ions formed during an irradiation period is monitored by conversion to the coloured tris-phenanthroUne complex Fe(phen) (s= 11,100 L mol cm at = 510 nm). The original Fe ions are not 

Because of the large experimental errors, the use of the ferrioxalate actinometer for excitation wavelengths higher than 450 nm is not recommended. 

Procedure—Potassium ferrioxalate can be easily synthesized as indicated in [8], and purified by recrystallization (three times). 

The same amount of phenanthroline solution is added to an aliquot of the irradiated solution and to an equal volume of the actinometric solution kept in the dark and then the solutions are brought to an appropriate final volume. The difference in absorbanee at 510 nm between the irradiated and dark solutions, AA(510), is measured. From Eqs. 4.8 and 4.12 the following equations for the incident flux are derived  

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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 quantum yield for the potassium ferrioxalate actinometer as a function of wavelength is shown in Table 2.8. 

The quantum yield of an actinometer may be affected by temperature. For potassium ferrioxalate this temperature effect is very small, as indicated in Table 2.9. 

This result may be substituted into Eq. 15-40 to calculate Oir(A). Classical actinometers that are used in this way include the potassium ferrioxalate actinometer that can be employed both in the uv and visible spectral region the Reinecke s salt actinometer (visible region), and the ort/io-nitrobenzaldehyde actinometer (uv region). For further description of these actinometers we refer to the literature (e.g., Leifer, 1988, pp. 148-151). 

The output of a lamp may be monitored by chemical actinometry. The standard method remains the irradiation of potassium ferrioxalate which is useful in the range 254 to 480 nm. The method is described in detail by Calvert and Pitts (1966) and by Murov (1973). But perhaps, the most convenient way to check the lamp output is to keep a stock solution of a model compound or the reagent itself, if it is readily available, and determine its rate of photolysis periodically by irradiation in a spectrophotometer cuvet. In this way the output of the lamp in the region of interest can be rapidly checked. An alternative is to use one of many radiation measuring instruments that are commercially available, a thermopile and voltmeter, for example (see Appendix for a list of manufacturers). 

It should be mentioned, that solar photolysis of ferrioxalate is of importance within atmospheric water droplets (cf. Sigg and Stumm, 1996). Potassium ferrioxalate... 

A = 253.7nm Parabolic cylinder. Made of Aluminum, specularly finished Measured by actinometry (potassium ferrioxalate) (13.9-5.45-2.33) x 10 Einstein cm s ... 

For a laboratory reactor like the one used in this work, these values can be obtained resorting to conventional acfinometry employing the well-known potassium ferrioxalate reaction. The details of the method can be found in Zalazar et al. (2005). The obtained results for the boundary conditions are indicated in Table 6. 

Incident radiation at the wall Operation Measured by actinometry (potassium ferrioxalate) 100% (without filters) 7.55 X 10 Einstein cm s (at each window) Calculated with a superficial emission model... 

The potassium ferrioxalate actinometer developed by Hatchard et al. (10,11) in the 1950s is probably the most widely used and most thoroughly investigated solution-phase actinometer [Ref. (9) and references therein]. Irradiation of an aqueous solution (0.006-0.15M) of K3Fe(C20 )j-3H20 with radiation between 250 and 470run (vide infra) results in a two-step photoreduction of iron (III) to iron (11) with quantum yields higher than unity, i.e.. 

Gruter H. Measuring the pulse energy of a nitrogen laser with the potassium ferrioxalate actinometer. J Appl Phys 1980 51 5204—5206. 

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

Y. Quan, S. Pehkonen, and M.B. Ray, Evaluation of three different lamp emission models using novel application of potassium ferrioxalate actinometry, Ind. Eng. Chem. Res. 43, 948-955 (2004). 

The photoreduction of potassium ferrioxalate is a classical example whose kinetic behavior can be summarized by a single photochemical step of the... 

C. G. Hatchard and C. A. Parker, A new sensitive chemical actionometer. II. Potassium ferrioxalate as a standard chemical actinometer, Proc. Roy. Soc. (London) A235, 581 (1956). 

Experimental details 55 The quantum yields of the reactions shown in Scheme 6.98 were obtained by simultaneous irradiation of the corresponding 4-nitroanisole amine solutions in methanol water (20 80, v/v) and actinometer (Section 3.9.2) solutions (aqueous potassium ferrioxalate) in UV cells, placed in a merry-go-round apparatus (Figure 3.30). The samples were irradiated by passing the light from a... 

Fig. 6A.11. Three-dimensional response surface representation of the diuron degradation as a function of potassium ferrioxalate and hydrogen peroxide concentrations.

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