Influence of pH upon the photolysis of the uranyl oxalate actinometer system

Abstract

A study has been made at 25" of the influence of pH upon the relative quantum yields for the consumption of oxalate and the production of carbon dioxide, carbon monoxide, and uranous ion by light of 254 nm absorbed by the uranyl oxalate actinometer system. The uranyl ion was at 0.01 F , the oxalate at 0.06 F , and initial pH was at 0-6. About 12% of the oxalate was decomposed. The quantum yields for the consumption of oxalate were found to be independent of the pH between 1 and 5 but to decrease outside this range. The reaction at all values of pH was found to consume acid. The moles of carbon dioxide produced in all forms (COZ, H&Oa, HCOa' , COa2-and the uranyl carbonate complexes) per mole of oxalate consumed very nearly equalled unity at pH 0 to 5. The moles of carbon monoxide produced per mole of oxalate consumed were always less than unity; they decreased with increase in pH abruptly between pH 1 and 2, and became negligible above pH 3. The mole ratio of uranous ion produced to oxalate consumed increased slowly from about 0.03 between pH 1.5 and 4 to about 0.08 at pH 6. The mechanisms of the reactions are discussed.

Formaldehyde degradation in the presence of methanol by photo-Fenton process

“…The photochemical reactor was purchased from ACE Glass Co. A 10 W low-pressure mercury lamp with a principal wavelength of 254 nm was used as the light source in all experiments. The intensity of the incident light inside the photo reactor was measured as 0.50 Â 10 À6 Einstein s À1 by uranil actinometer method (Heidt et al, 1979). The UV lamp was inserted into a double-walled quartz immersion-well located at the center of the reactor.…”

A comparative study of the advanced oxidation of 2,4-dichlorophenol

“…The radiation flux entering the reactor was determined by actinometric experiments based on the photochemical decomposition of oxalic acid in the presence of uranyl ion [13]. For 350 nm wavelength, the quantum yield of this system is equal to 0.51 mol Einstein −1 .…”

Free-radical redox reactions of uranium ions in sulphuric acid solutions

“…As a check, the maximum yield of uranium(1V) was confirmed by photolytically reducing the uranyl ions. This was not possible when oxalate was present, as photolysis of these solutions forms CO and C 0 2 but very little uranium(1V) (4). In the cases where tert-butanol or gluconate were present, complete reduction by radiolysis was not always possible; however, the extinction coefficient of uranium(1V) was determined by the complete photolytic reduction of uranyl ions in these solutions.…”

“…Depending on the pH of the solution, the organic solute (S) present, and how far the reduction of the uranyl ions has proceeded, the solvated electrons will be scavenged either by the uranyl ions or the organic solute to form uranium(V) (reactions [2]- [4]), or will be scavenged by the protons to form hydrogen atoms (reaction [5]). [5] H+ + e-,,+ H k5 = 2 x L mol-' s-I (9) These hydrogen atoms formed through [I] and [5] will either reduce the uranyl ions, or react with the organic solute present.…”