Chemical and electrochemical contributions to the redox-sorption of oxygen from water on granular layers of copper-containing nanocomposites
Abstract
Metal nanoparticles demonstrate noticeable sorption and redox properties in porous polymer matri-ces. Deep deoxygenation of water is based on these properties of metal-polymer nanocomposites (NC). Earli-er studies demonstrated a significant contribution of the electrochemical component to the process of oxygen reduction on a thin cathode-polarised granular layer of a copper-containing nanocomposite. During the early stage, the process is limited by the stage of external diffusion of oxygen towards the surface of the nanocom-posite’s granules. Further process is marked by the growing contribution of the chemical component. The characteristic feature of this component is that it limits the process by means of internal diffusion stage of oxygen transfer to copper nanoparticles and uses electric current for the electroreduction of metal oxides. However, when transferring from thin films and layers to granular layers of an NC of the column type with vertically distributed kinetic parameters, the proportion of electrochemical and chemical contributions should be studied further.
In our study, we investigated the redox-sorption of oxygen from water on dynamic granular layers of copper – sulfocation exchanger nanocomposites (KU-23, Lewatit K2620) at various polarisation currents and evaluated the contributions of the chemical and electrochemical components to the stationary period.
We determined that the amount of absorbed oxygen depends extremely on the strength of the polari-sation current of the limiting polarisation. The products of the metal nanoparticles oxidation were observed in the form of island clusters. The oxidation of some granules is accompanied by the formation of the bounda-ries of oxide layers of the same height as the granular layer. The higher the granular layer and the stronger the limiting polarising current, the more quasistationary the oxygen absorption process is. The study also demonstrated that the contributions of the chemical and electrochemical paths of the oxygen reduction are compatible, when the process lasts long (100 hours). Some oxygen is absorbed through the reaction of elec-troreduction on copper particles mainly on the surface of the granules of the nanocomposite. The rest is ab-sorbed by means of an autocatalytic chemical reaction of oxygen with electro-regenerated metal nanoparti-cles contained in the nanocomposite granules. The probability of each process depends on the state of the system and the current strength. The stationary mode of redox-sorption of oxygen from water is established due to the constant electro-generation of hydrogen ions and electro-regeneration of copper nanoparticles re-quired for the reduction of oxygen.
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References
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