A Green Method to Determine VUV (185 nm) Fluence Rate Based on Hydrogen Peroxide Production in Aqueous Solution

A mini-fluidic vacuum ultraviolet/ultraviolet (VUV/UV) photoreaction system (MVPS) was developed in our previous study. Based on the MVPS, a green method to determine VUV fluence rate has been developed using the production rate of H₂ O₂ when water is exposed to 185 nm VUV. The H₂ O₂ production followed pseudo-zero-order reaction kinetics well over the first 10 min of VUV/UV exposure. This new method was well calibrated with a standard cis-cyclooctene cis-trans photoisomerization actinometer as recommended by the International Union of Pure and Applied Chemistry. The apparent quantum yield for H₂ O₂ production by 185 nm VUV irradiation of water was determined to be 0.024 ± 0.002. As the solution pH increased from 5.0 to 8.0, the H₂ O₂ production rate decreased from 0.83 to 0.40 μm min^-1 . Dissolved oxygen had a negligible influence on the H₂ O₂ production. This study proposes a novel VUV fluence rate determination method with advantages of nontoxicity, low detection limits, low costs and convenience, and it can be used as a good alternative to traditional actinometers.