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Aqueous photo(electro)catalysis with eumelanin thin films
Univ Naples Federico II, Italy.
Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering. Rudjer Boskovic Inst, Croatia.
Univ Naples Federico II, Italy; CNR, Italy; Natl Interuniv Consortium Mat Sci and Technol INSTM, Italy.
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2018 (English)In: Materials Horizons, ISSN 2051-6347, E-ISSN 2051-6355, Vol. 5, no 5, p. 984-990Article in journal (Refereed) Published
Abstract [en]

We report that eumelanin, the ubiquitous natural pigment found in most living organisms, is a photocatalytic material. Though the photoconductivity of eumelanin and its photochemical reactions with oxygen have been known for some time, eumelanins have not been regarded as photofaradaic materials. We find that eumelanin shows photocathodic behavior for both the oxygen reduction reaction and the hydrogen evolution reaction. Eumelanin films irradiated in aqueous solutions at pH 2 or 7 with simulated solar light photochemically reduce oxygen to hydrogen peroxide with accompanying oxidation of sacrificial oxalate, formate, or phenol. Autooxidation of the eumelanin competes with the oxidation of donors. Deposition of thin films on electrodes yields photoelectrodes with higher photocatalytic stability compared with the case of pure photocatalysis, implicating the successful extraction of positive charges from the eumelanin layer. These results open up new potential applications for eumelanin as a photocatalytically-active biomaterial, and inform the growing fundamental body of knowledge about the physical chemistry of eumelanins.

Place, publisher, year, edition, pages
ROYAL SOC CHEMISTRY , 2018. Vol. 5, no 5, p. 984-990
National Category
Theoretical Chemistry
Identifiers
URN: urn:nbn:se:liu:diva-151797DOI: 10.1039/c8mh00715bISI: 000444245600023OAI: oai:DiVA.org:liu-151797DiVA, id: diva2:1253310
Note

Funding Agencies|Knut and Alice Wallenberg Foundation; Italian Project RELIGHT [PON02_00556_3306937]

Available from: 2018-10-04 Created: 2018-10-04 Last updated: 2020-02-25
In thesis
1. Organic electronic materials for hydrogen peroxide production
Open this publication in new window or tab >>Organic electronic materials for hydrogen peroxide production
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Hydrogen peroxide (H2O2) is an important oxidant, used in various fields of industry, such as paper manufacturing, production of polymers, detergents, and cosmetics. Considering that the molecule degrades only to H2O and O2, it is regarded as a green chemical. Unfortunately, the incumbent method of H2O2 synthesis, based on anthraquinone oxidation, although efficient, is not environmentally friendly, as it requires fossil fuels and significant energy input. Therefore, there are efforts underway to reduce the ecological impact of hydrogen peroxide production. Some of the most promising approaches involve catalytic reduction of O2 to H2O2 in an aqueous environment. This can be coupled with water oxidation. As the required energy could be delivered in different ways, hydrogen peroxide synthesis can be achieved by electrocatalysis, photoelectrocatalysis, or photocatalysis.

This thesis explores the possibility of using organic electronic materials as catalysts for H2O2 evolution in oxygenated water solutions. Organic electronics is a field of materials science focused on conducting and semiconducting organic molecules. These materials offer many possible advantages, related to low cost, flexibility, and good optoelectronic properties. Huge progress in the field over the last years led to their commercial applications in e.g. organic light emitting diodes and photovoltaics. Only very recently have organic electronics begun to be considered from the point of view of catalysis.

In the first two papers, we investigate electrocatalytic activity of an organic pigment (PTCDI) and a conducting polymer (PEDOT) towards oxygen reduction to hydrogen peroxide. Both types of catalysts are chemically stable and able to operate in a wide pH range. In paper 3, we demonstrate that H2O2-evolving photocathodes can be based on an organic PN heterojunction, giving devices of a record-breaking performance. In the first part of paper 4, the same concept was tested for a naturally-occurring semiconductor, eumelanin, leading to a first report of photoelectrocatalytic properties of this material. In the second part of paper 4, as well as in papers 5 and 6, we explore, respectively, photochemical hydrogen peroxide synthesis with eumelanin, organic semiconductors, and organic dyes. We show that the photostability of catalysts is higher for materials with low-lying HOMO level and it can be increased by an addition of a reducing agent to the reaction system. Our findings prove that already existing organic electronic materials can be successfully applied in H2O2 evolution for environmentally friendly chemical synthesis, suggesting their use in harvesting of solar energy and in situ generation of hydrogen peroxide for biomedical applications.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2020. p. 92
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 2037
Keywords
hydrogen peroxide, catalysis, organic materials, electronics
National Category
Materials Chemistry
Identifiers
urn:nbn:se:liu:diva-163895 (URN)978-91-7929-939-2 (ISBN)
Public defence
2020-03-30, K1, Kåkenhus, Campus Norrköping, Norrköping, 10:15 (English)
Opponent
Supervisors
Funder
Knut and Alice Wallenberg Foundation, WCMM-LiU
Available from: 2020-02-25 Created: 2020-02-25 Last updated: 2020-02-25Bibliographically approved

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