Potassium tris(oxalato) ferrate(III) trihydrate (K3[Fe(C2O4)3]•3H2O) and sulfuric acid (H2SO4) were dissolved in deionized water to prepare the solution including 4.0 × 10-4-3.0 × 10-2 M of potassium tris(oxalato) ferrate(III) (K3[Fe(C2O4)3]) and 5.0 × 10-2 M of H2SO4. Measuring the consumed powers of LED by the digital multi-meter, the all light from LED was irradiated into the 50-cm optical cell filled with the solution including K3[Fe(C2O4)3] and H2SO4. Here the area of irradiation light from LED was typically about 2.3 cm 2. An aliquot of 10 mL of the solution after the irradiation was diluted by 65.0 mL of deionized water to which 9.91 mg of 1,10phenanthroline (C12N2H8) and 25.0 mL of sulfur acid-sodium acetate buffer solution was added. The buffer solution was prepared with 0.180 M of H2SO4 and 0.6 M of sodium acetate (CH3CO2Na). The mixed solution was sufficiently stirred and was then left to stand in a dark place. After standing for more than a half hour, the solution was poured into a 1-cm square cell and then the absorption spectrum of the solution was measured in the range of 400-700 nm by the absorption spectrophotometer (K-MAC: Lab-Junior). The concentration of tris(1,10-phenantholine) iron(II) ([Fe(C12N2H8)3] 2+), which is generated by the complex formation of Fe(II) 2+ ion and C12N2H8 was determined using the value of absorbance at 510 nm where [Fe(C12N2H8)3] 2+ has the absorption peak and the reported molar absorption coefficient of [Fe(C12N2H8)3] 2+. S 1 Here, the values of the quantum yield for the formation of Fe(II) 2+ at 365, 405, 436, 468, 480 and 509 nm are reported by Hatchard and Parker S 2. In present work, the values of the quantum yield for the formation of Fe(II) 2+ at 375, 405, 430, 450 and 470 nm that were necessary to measure photon flux of LEDs by Hatchard-Parker actinometer were not reported. Thus, these values were estimated to be 1.17 at 375 nm, 1.10 at 405 nm, 1.04 at 430 nm, 0.99 at 450 nm and 0.94 at 470 nm by using an interpolation method with the reported values of the quantum yield. Using the concentration of [Fe(C12N2H8)3] 2+ which is the same concentration as the concentration of Fe(II) 2+ ion photogenerated from K3[Fe(C2O4)3] by LED irradiation and the reported quantum yield of the photolysis of K3[Fe(C2O4)3], S2 the photon flux from LED could be determined.
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