Self-oscillating Water Chemiluminescence Modes and Reactive Oxygen Species Generation Induced by Laser Irradiation; Effect of the Exclusion Zone Created by Nafion.

Sergey Gudkov,Vadim Bruskov,Valeriy Kozlov,Maxim Astashev,Stanislav Zakharov,Nikolai Bunkin

doi:10.3390/e16116166

Abstract

Samples of water inside and outside an exclusion zone (EZ), created by Nafion swollen in water, were irradiated at the wavelength l = 1264 nm, which stimulates the electronic transition of dissolved oxygen from the triplet state to the excited singlet state. This irradiation induces, after a long latent period, chemiluminescence self-oscillations in the visible and near UV spectral range, which last many hours. It occurs that this effect is EZ-specific: the chemiluminescence intensity is twice lower than that from the bulk water, while the latent period is longer for the EZ. Laser irradiation causes accumulation of H2O2, which is also EZ-specific: its concentration inside the EZ is less than that in the bulk water. These phenomena can be interpreted in terms of a model of decreasing O2 content in the EZ due to increased chemical activity of bisulfite anions (HSO3-), arisen as the result of dissociation of terminal sulfonate groups of the Nafion. The wavelet transform analysis of the chemiluminescence intensity from the EZ and the bulk water gives, that self-oscillations regimes occurring in the liquid after the latent period are the determinate processes. It occurred that the chemiluminescence dynamics in case of EZ is characterized by a single-frequency self-oscillating regime, whereas in case of the bulk water, the self-oscillation spectrum consists of three spectral bands.

Highlights

At present the proton-exchange membrane Nafion®, developed by the DuPontTM Company, is widely used in the manufacture of low-temperature (i.e., < 1000 °С) hydrogen fuel cells [1]
In our recent works [14,15] we show that the water layer adjacent to the Nafion interface has an increased refractive index; it was found that the exclusion zone (EZ) water exhibits birefringence properties, which implies the quasi-crystalline structure of that liquid
After irradiation at this wavelength we can distinguish three phases of the chemiluminescence from water: the latent period, when the average intensity of the emission corresponds to the background level, the growth and reaching the steady-state level of the chemiluminescence intensity; the latter regime is characterized by the self-oscillatory modes

Summary

Introduction

At present the proton-exchange membrane Nafion®, developed by the DuPontTM Company, is widely used in the manufacture of low-temperature (i.e., < 1000 °С) hydrogen fuel cells [1]. Its unique ionic properties result from incorporation of perfluorovinyl ether groups terminated with sulfonate groups onto a tetrafluoroethylene backbone [2] (Figure 1). I.e., the internal interface of those channels appears to be charged negatively. This is why the positive ions are attracted to the channels, while the negative ions are repelled, which gives rise to the ion-exchange properties of the membrane. This phenomenon has attracted much interest from biophysicists, since cell membranes behave —selectively transmitting ions of a certain type, and repelling the ions of other type [3]. Nafion, being in contact with water, exhibits well expressed hydrophilic properties, i.e., it should affect the near-surface molecular layers of water. The conventional point of view concerning the hydrophilic hydration radius (i.e., the spatial scale, where the molecular structure of water, contacted with a solid interface, can be treated as an ordered one) consists in this size is about several tens of nanometers due to the effect of the short-range dispersion forces

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