Generation of Reactive Oxygen Species via Electroprotic Interaction of H 2 O 2 with ZrO 2 Gel: Ionic Sponge Effect and pH-Switchable Peroxidase- and Catalase-Like Activity
2017; American Chemical Society; Volume: 7; Issue: 4 Linguagem: Inglês
10.1021/acscatal.7b00189
ISSN2155-5435
AutoresKamila Sobańska, Piotr Pietrzyk, Zbigniew Sojka,
Tópico(s)Electrochemical Analysis and Applications
ResumoFormation of reactive oxygen species (ROS) is of vital importance in catalytic oxidation chemistry. In this paper we have shown that a nonredox system such as amorphous zirconium dioxide (a-ZrO2) is highly active in ROS formation via H2O2 decomposition. Interaction between a-ZrO2 and H2O2 in aqueous solution was investigated by means of EPR, HYSCORE, Raman, and UV–vis, along with auxiliary FTIR, TG-MS, and XPS techniques, in a broad range of pH values and H2O2 concentrations. Various reaction intermediates such as superoxide (O2•–) and hydroxyl (•OH) radicals as well as peroxide (O22–) species were identified. At pH 5.3 formation of O22– is accompanied by a substantial release of O2 due to the pronounced catalase-like activity of a-ZrO2. The role of electroprotic processes (an interfacial proton transfer coupled with an intermolecular electron transfer) in H2O2 decomposition and ROS formation was elucidated, and a plausible mechanism of this reaction, ≡Zr+–HO2–(surf) + H2O2(aq) → •OH(aq) + ≡Zr+–O2•–(surf) + H2O, was proposed. The surface of a-ZrO2 covered with hydroxyl groups plays a role of an ionic sponge, which controls the electroprotic equilibrium by capturing the charged reaction intermediates. Unlike the amorphous gel, crystalline zirconia exhibits only weak activity in the production of the O2•– and •OH radicals, and a different mechanism is involved. It is worth mentioning that the activity of the zirconia gel catalyst in ROS generation, as gauged by the Michaelis–Menten constant, is comparable (ca. 40%) to that of the Fenton-type oxides (Fe3O4, Co3O4).
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