Nature Reviews Materials 2, Article number: 17030 (2017)

doi:10.1038/natrevmats.2017.30

Fabian K. Kessler, Yun Zheng, Dana Schwarz, Christoph Merschjann, Wolfgang Schnick, Xinchen Wang & Michael J. Bojdys

In the past decade, research in the field of artificial photosynthesis has shifted from simple, inorganic semiconductors to more abundant, polymeric materials. For example, polymeric carbon nitrides have emerged as promising materials for metal-free semiconductors and metal-free photocatalysts. Polymeric carbon nitride (melon) and related carbon nitride materials are desirable alternatives to industrially used catalysts because they are easily synthesized from abundant and inexpensive starting materials. Furthermore, these materials are chemically benign because they do not contain heavy metal ions, thereby facilitating handling and disposal. In this Review, we discuss the building blocks of carbon nitride materials and examine how strategies in synthesis, templating and post-processing translate from the molecular level to macroscopic properties, such as optical and electronic bandgap. Applications of carbon nitride materials in bulk heterojunctions, laser-patterned memory devices and energy storage devices indicate that photocatalytic overall water splitting on an industrial scale may be realized in the near future and reveal a new avenue of ‘post-silicon electronics’.

A. Indra, A. Acharjya, P. W. Menezes, C. Merschjann, D. Hollmann, M. Schwarze, M. Aktas, A. Friedrich, S. Lochbrunner, A. Thomas, M. Driess,
Angew. Chem. Int. Ed. 2017, 56, 1653
DOI: 10.1002/anie.201611605

Solar light harvesting by photocatalytic H₂ evolution from water could solve the problem of greenhouse gas emission from fossil fuels with alternative clean energy. However, the development of more efficient and robust catalytic systems remains a great challenge for the technological use on a large scale. Here we report the synthesis of a sol–gel prepared mesoporous graphitic carbon nitride (sg-CN) combined with nickel phosphide (Ni₂P) which acts as a superior co-catalyst for efficient photocatalytic H₂ evolution by visible light. This integrated system shows a much higher catalytic activity than the physical mixture of Ni₂P and sg-CN or metallic nickel on sg-CN under similar conditions. Time-resolved photoluminescence and electron paramagnetic resonance (EPR) spectroscopic studies revealed that the enhanced carrier transfer at the Ni₂P–sg-CN heterojunction is the prime source for improved activity.

Azhr A. Raheem^1,2,3, Martin Wilke^1,2, Mario Borgwardt^1,2, Nicholas Engel^1,2, Sergey I. Bokarev^4,a), Gilbert Grell⁴, Saadullah G. Aziz⁵, Oliver Kühn⁴, Igor Yu. Kiyan², Christoph Merschjann^1,2,b), and Emad F. Aziz^1,2,6,c)

Structural Dynamics 4, 044031 (2017); doi: http://dx.doi.org/10.1063/1.4990567

The kinetics of ultrafast photoinduced structural changes in linkage isomers is investigated using Na₂[Fe(CN)₅NO] as a model complex. The buildup of the metastable side-on configuration of the NO ligand, as well as the electronic energy levels of ground, excited, and metastable states, has been revealed by means of time-resolved extreme UV (XUV) photoelectron spectroscopy in aqueous solution, aided by theoretical calculations. Evidence of a short-lived intermediate state in the isomerization process and its nature are discussed, finding that the complete isomerization process occurs in less than 240 fs after photoexcitation.