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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.

Abstract [sv]

Väteperoxid (H2O2) är en viktig oxidant som används inom olika industrier, såsom papperstillverkning och produktion av polymerer, tvättmedel och kosmetika. Med tanke på att molekylen bryts ner till vatten (H2O) och syre (O2) betraktas den som en grön kemikalie. Tyvärr är den befintliga metoden för framställning av H2O2 baserad på oxidation av en antrakinon, en metod som är effektiv, men inte miljövänlig eftersom den kräver fossila bränslen och betydande energitillförsel. Det pågår därför ansträngningar för att minska den ekologiska effekten av väteperoxidproduktionen. Några av de mest lovande metoderna involverar katalytisk O2 till H2O2-reduktion i vattenlösning, kombinerat med vattenoxidation. Eftersom den nödvändiga energin kan levereras på olika sätt kan väteperoxidsyntesen uppnås genom elektrokatalys, fotoelektrokatalys eller fotokatalys.

Denna avhandling undersöker möjligheten att använda organiska elektroniska material som katalysatorer för framställning av H2O2i syresatta vattenlösningar. Organisk elektronik är ett område inom materialvetenskap med fokus på ledande och halvledande organiska molekyler. Dessa material erbjuder många fördelar, såsom låg kostnad, flexibilitet och goda optoelektroniska egenskaper. Enorma framsteg på området har under de senaste åren lett till deras kommersiella tillämpningar i till exempel organiska ljusemitterande dioder och fotovoltaik. Nyligen har också organisk elektronik börjat övervägas ur katalysens synvinkel.

I de två första artiklarna undersöker vi en elektrokatalytisk aktivitet av ett organiskt pigment (PTCDI) och en ledande polymer (PEDOT) i respekt till syrereduktion och väteperoxidproduktion. Båda typerna av katalysatorer är kemiskt stabila och kan arbeta inom ett brett pH-område. I artikel 3 visar vi att H2O2-producerande fotokatoder kan baseras på en organisk PN-gränsyta, vilket ger enheter med en rekordbrytande kapacitet. I den första delen av artikel 4 testades samma koncept för en naturligt förekommande halvledare, eumelanin, vilket ledde till en första rapport om fotoelektrokatalytiska egenskaper hos detta material. I den andra delen av artikel 4, samt i artikel 5 och 6, undersöker vi fotokemisk väteperoxidsyntes med eumelanin, organiska halvledare och organiska färgämnen. Vi visar att fotostabiliteten hos katalysatorer är högre för material med lågt liggande HOMO-nivå och att den kan ökas genom en tillsats av ett reduktionsmedel till reaktionssystemet. Våra fynd visar att redan befintliga organiska elektroniska material framgångsrikt kan tillämpas i H2O2-utvecklingen för miljövänlig kemisk syntes, vilket antyder att de kan användas för att ta tillvara på solenergi och för produktion av väteperoxid inom biomedicin.

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)10.3384/diss.diva-163895 (DOI)9789179299392 (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: 2020-03-02Bibliographically approved

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