Authors
- Dariusz Mitoraj Ulm University ,
- Igor Krivtsov Ulm University ,
- Chunyu Li Friedrich Schiller University Jena ,
- Ashwene Rajagopal Ulm University ,
- Changbin Im Ulm University ,
- Christiane Adler Ulm University ,
- Kerstin Köble Ulm University ,
- Olena Khainakova University of Oviedo ,
- Julian Hniopek Friedrich Schiller University Jena ,
- Christof Neumann Friedrich Schiller University Jena ,
- Andrey Turchanin Friedrich Schiller University Jena ,
- Ivan da Silva Rutherford Appleton Laboratory ,
- Michael Schmitt Friedrich Schiller University Jena ,
- Robert Leiter Ulm University ,
- Tibor Lehnert Ulm University ,
- Jürgen Popp Friedrich Schiller University Jena ,
- Ute Kaiser Ulm University ,
- Timo Jacob Ulm University ,
- Carsten Streb Ulm University ,
- Benjamin Dietzek Friedrich Schiller University Jena ,
- Radim Beranek
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Ulm University
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. Our work thus highlights the importance of careful determination of structural features governing the complex interplay between the light absorption, charge separation and catalytic turnover in PCN-based polymers tailored for visible light-driven photocatalysis.
Content
