Ultraviolet (UV) light effect on the electrical potential of interfacial water

Abstract

Water is one of the most essential elements of life. Despite many studies on the physical and chemical properties of water, many features are still not yet understood. Here, we consider the negative electrical potential in the water adjacent to the Nafion membrane. The electrical potential becomes more negative closer to the membrane, a feature that might arise from the special water structure (interfacial water) next to Nafion. Evidence has shown that the water was characterized by a UV absorbance at ∼270 nm. We hypothesized that such radiant energy might contribute to the electrical potential of the interfacial water. Here, the effect of exposure to light on this potential, at wavelengths of 275 nm, 370 nm and 650 nm was studied. The electrical potential became more negative under 275 nm wavelength UV light, while other two wavelengths had negligible effects. The result fits well with the ∼270 nm wavelength absorption peak reported in previous studies. Potentially, the absorbed UV energy helps fuel the ‘water battery’. The findings shed light on the mechanism underlying the character of interfacial water adjacent to hydrophilic surfaces.