Ferrioxalate-Polyoxometalate System as a New Chemical Actinometer

A chemical actinometer that employs an aqueous solution of ferrioxalate and polyoxometalate (POM: SiW12O404-) is proposed as a simple and fast method that quantifies the light intensity of UV radiation in the 300−390 nm range. As a modified ferrioxalate actinometer, illuminated ferrioxalate solution in the presence of POM generates CO2 radical anions that lead to the production of blue-colored POM- (SiW12O405-) whose concentration can be easily determined spectrophotometrically (by monitoring absorbance at 730 nm). Photoproduction rate of POM- is linearly correlated with the light intensity. The measured quantum yields, Φ(POM-), range 0.11−0.21 in the 300−390 nm region and is fairly constant around 0.18 in the 335−380 nm range, which makes this actinometry ideally suited for the rapid measurement of the light intensity in the UVA region such as in common black light sources. This alternative actinometry eliminates the postirradiation analytical procedure (which needs phenanthroline as a complexation reagent for Fe2+ and the subsequent color development) that is required in the standard ferrioxalate actinometry, and it enables the in-situ quantification of the light intensity in a simpler way by monitoring the formation of POM- as a proxy indicator.