A Study in Red: The Overlooked Role of Azo-Moieties in Polymeric Carbon Nitride Photocatalysts with Strongly Extended Optical Absorption

Mitoraj D, Krivtsov I, Li C, Rajagopal A, Im C, Adler C, Koble K, Khainakova O, Hniopek J, Neumann C, Turchanin A, Da Silva I, Schmitt M, Leiter R, Lehnert T, Popp J, Kaiser U, Jacob T, Streb C, Dietzek B, Beranek R (2021)

Publication Type: Journal article

Publication year: 2021

Journal

Chemistry - A European Journal Wiley

Book Volume: 27

Pages Range: 17188-17202

Journal Issue: 68

DOI: 10.1002/chem.202102945

Abstract

The unique optical and photoredox properties of heptazine-based polymeric carbon nitride (PCN) materials make them promising semiconductors for driving various productive photocatalytic conversions. However, their typical absorption onset at ca. 430–450 nm is still far from optimum for efficient sunlight harvesting. Despite many reports of successful attempts to extend the light absorption range of PCNs, the determination of the structural features responsible for the red shift of the light absorption edge beyond 450 nm has often been obstructed by the highly disordered structure of PCNs and/or low content of the moieties responsible for changes in optical and electronic properties. In this work, we implement a high-temperature (900 °C) treatment procedure for turning the conventional melamine-derived yellow PCN into a red carbon nitride. This approach preserves the typical PCN structure but incorporates a new functionality that promotes visible light absorption. A detailed characterization of the prepared material reveals that partial heptazine fragmentation accompanied by de-ammonification leads to the formation of azo-groups in the red PCN, a chromophore moiety whose role in shifting the optical absorption edge of PCNs has been overlooked so far. These azo moieties can be activated under visible-light (470 nm) for H2 evolution even without any additional co-catalyst, but are also responsible for enhanced charge-trapping and radiative recombination, as shown by spectroscopic studies.

Involved external institutions

Universität Ulm DE Germany (DE) Friedrich-Schiller-Universität Jena DE Germany (DE) Universidad de Oviedo ES Spain (ES) Rutherford Appleton Laboratory GB United Kingdom (GB)

How to cite

APA:

Mitoraj, D., Krivtsov, I., Li, C., Rajagopal, A., Im, C., Adler, C.,... Beranek, R. (2021). A Study in Red: The Overlooked Role of Azo-Moieties in Polymeric Carbon Nitride Photocatalysts with Strongly Extended Optical Absorption. Chemistry - A European Journal, 27(68), 17188-17202. https://dx.doi.org/10.1002/chem.202102945

MLA:

Mitoraj, Dariusz, et al. "A Study in Red: The Overlooked Role of Azo-Moieties in Polymeric Carbon Nitride Photocatalysts with Strongly Extended Optical Absorption." Chemistry - A European Journal 27.68 (2021): 17188-17202.

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