Twinned Growth of Metal-Free, Triazine-Based Photocatalyst Films as Mixed-Dimensional (2D/3D) van der Waals Heterostructures

Schwarz, D.; Noda, Y.; Klouda, J.; Schwarzová-Pecková, K.; Tarábek, J.; Rybáček, J.; Janoušek, J.; Simon, F.; Opanasenko, M. V.; Čejka, J.; Acharjya, A.; Schmidt, J.; Selve, S.; Reiter-Scherer, V.; Severin, N.; Rabe, J. P.; Ecorchard, P.; He, J.; Polozij, M.; Nachtigall, P.; Bojdys,* M. J. Adv. Mater. 2017, DOI: 10.1002/adma.201703399

Design and synthesis of ordered, metal-free layered materials is intrinsically difficult due to the limitations of vapor deposition processes that are used in their making. Mixed-dimensional (2D/3D) metal-free van der Waals (vdW) heterostructures based on triazine (C3N3) linkers grow as large area, transparent yellow-orange membranes on copper surfaces from solution. The membranes have an indirect band gap (Eg,opt = 1.91 eV, Eg,elec = 1.84 eV) and are moderately porous (124 m2 g−1). The material consists of a crystalline 2D phase that is fully sp2 hybridized and provides structural stability, and an amorphous, porous phase with mixed sp2–sp hybridization. Interestingly, this 2D/3D vdW heterostructure grows in a twinned mechanism from a one-pot reaction mixture: unprecedented for metal-free frameworks and a direct consequence of on-catalyst synthesis. Thanks to the efficient type I heterojunction, electron transfer processes are fundamentally improved and hence, the material is capable of metal-free, light-induced hydrogen evolution from water without the need for a noble metal cocatalyst (34 µmol h−1 g−1 without Pt). The results highlight that twinned growth mechanisms are observed in the realm of “wet” chemistry, and that they can be used to fabricate otherwise challenging 2D/3D vdW heterostructures with composite properties.

DOI: 10.1002/adma.201703399

Tailored band gaps in sulphur and nitrogen containing porous donor-acceptor polymers (SNPs)

Schwarz, D.; Kochergin, Y. S.; Acharja, A.; Ichangi, A.; Opanasenko, M. V.; Čejka, J.; Lappan, U.; Arki, P.; He, J.; Schmidt, J.; Nachtigall, P.; Thomas, A.; Bojdys,* M. J. Chem. – Eur. J. 2017, DOI: 10.1002/chem.201703332

Donor-acceptor dyads hold the key to tuning of electrochemical properties and enhanced mobility of charge carriers, yet their incorporation into a heterogeneous polymer network proves difficulty due to the fundamentally different chemistry of the donor- and acceptor-subunits. We present a family of sulphur and nitrogen containing porous polymers (SNPs) that are obtained via Sonogashira-Hagihara cross-coupling and that combine electron-withdrawing triazine (C3N3) and electron donating, sulphur-containing linkers. Choice of building blocks and synthetic conditions determines the optical band gap (from 1.67 to 2.58 eV) and nanoscale ordering of these microporous materials with BET surface areas of up to 545 m2 g-1 and CO2 capacities up to 1.56 mmol g-1. Our results highlight the advantages of the modular design of SNPs, and we report one of the highest photocatalytic hydrogen evolution rates for a cross-linked polymer without Pt co-catalyst (194 µmol h-1 g-1).

DOI: 10.1002/chem.201703332

Functional carbon nitride materials — design strategies for electrochemical devices

Kessler, F. K.; Zheng, Y.; Schwarz, D.; Merschjann, C.; Schnick, W.; Wang, X.; Bojdys,* M. J. Nature Reviews Materials 2017, Article number: 17030 (2017), DOI: 10.1038/natrevmats.2017.30

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’.

DOI: 10.1038/natrevmats.2017.30

Anionic silicate organic frameworks constructed from hexacoordinated silicon centres

Roeser,* J.; Dragica, P.; Bojdys, M. J.; Fayon, P.; Trewin, A.; Fitch, A. N.; Schmidt, M. U.; Thomas,* A. Nature Chemistry 2017, Advance Article, DOI: 10.1038/NCHEM.2771

Crystalline frameworks composed of hexacoordinated silicon species have thus far only been observed in a few high pressure silicate phases. By implementing reversible Si–O chemistry for the crystallization of covalent organic frameworks, we demonstrate the simple one-pot synthesis of silicate organic frameworks based on octahedral dianionic SiO6 building units. Clear evidence of the hexacoordinated environment around the silicon atoms is given by 29Si nuclear magnetic resonance analysis. Characterization by high-resolution powder X-ray diffraction, density functional theory calculation and analysis of the pair-distribution function showed that those anionic frameworks—M2[Si(C16H10O4)1.5], where M = Li, Na, K and C16H10O4 is 9,10-dimethyl-2,3,6,7-tetraolatoanthracene—crystallize as two-dimensional hexagonal layers stabilized in a fully eclipsed stacking arrangement with pronounced disorder in the stacking direction. Permanent microporosity with a two-step filling process was evidenced by gas-sorption measurements. The negatively charged backbone balanced with extra-framework cations and the permanent microporosity are characteristics that are shared with zeolites.

DOI: 10.1038/NCHEM.2771

Dicyano- and tetracyanopentacene: foundation of an intriguing new class of easy-to-synthesize organic semiconductors

Glöcklhofer, F.; Petritz, A.; Karner, E.; Bojdys, M. J.; Stadlober, B.; Fröhlich, J.; Unterlass, M. M. Journal of Materials Chemistry C 2017, Advance Article, DOI: 10.1039/C7TC00143F.

Cyanated pentacenes are very promising candidate materials for ambipolar and n-type transistors. However, only a few examples have been obtained to date – all requiring lengthy, multi-step processes. Herein, we present the first preparation of 5,7,12,14-tetracyanopentacene (TCP) and a facile, scaled-up preparation of 6,13-dicyanopentacene (DCP). Both compounds are prepared by a one-pot synthesis using cheap quinones as starting materials. Detailed crystallographic investigations evince that the bulk assemblies of both cyanated pentacenes are dominated by non-covalent interactions, resulting in a dense, stable, face-to-face packing and in an intriguing packing motif for TCP. Very low frontier molecular orbital energy levels and a reversible bleaching of TCP are revealed by cyclic voltammetry. Finally, both cyanated pentacenes are used in proof-of-concept organic thin-film transistors (OTFTs) operating under ambient conditions. This work highlights the potential of cyanation for larger acenes and presents a straightforward route to the rational design of this promising class of materials.

DOI: 10.1039/C7TC00143F

CUCAM Workshop

 

 

 

 

 

 

Want to find out more about the new “Charles University Center of Advanced Materials” (CUCAM)? Come along on the 8th of February to our kick-off workshop at Charles University, Department of Chemistry, Hlavova 8 in Prague!

 

Carbon nitride frameworks and dense crystalline polymorphs

Pickard, C. J.; Salamat, A.; Bojdys, M. J.; Needs, R. J.; McMillan, P. F. Physical Review B 2016, 94, 094104, DOI: 10.1103/PhysRevB.94.094104, arXiv:1605.02893.

Capture

We used ab initio random structure searching (AIRSS) to investigate polymorphism in C3N4 carbon nitride as a function of pressure. Our calculations reveal new framework structures, including a particularly stable chiral polymorph of space group P43212 containing mixed sp2 and sp3-bonding, that we have produced experimentally and recovered to ambient conditions. As pressure is increased a sequence of structures with fully sp3-bonded C atoms and three-fold coordinated N atoms is predicted, culminating in a dense Pnma phase above 250 GPa. Beyond 650 GPa we find that C3N4 becomes unstable to decomposition into diamond and pyrite-structured CN2.

DOI: 10.1103/PhysRevB.94.094104, arXiv:1605.02893

WO2016027042 (A1) – Two-dimensional carbon nitride material and method of preparation

Cooper, A. I. and Bojdys, M. J. (2016). Two-dimensional carbon nitride material and method of preparation. WO2016027042 (A1).

WOGB2014052568

Graphitic carbon nitride has been prepared and its structure confirmed by extensive characterization. This material has useful electronic, in particular semiconducting, properties. Crystalline thin films have been prepared. Synthesis may be carried out by condensation of unsaturated carbon- and nitrogen- containing compound(s) in inert solvent such as a salt melt, forming graphitic carbon nitride at a gas-liquid or solid-liquid interface.

External Links: Patentscope, Espacenet, Google Patents

“2D Materials – Beyond Silicone and Graphene” – by Mara Staffilani

Michael J. Bojdys, head of the Functional Nanomaterials group at the Charles University in Prague, describes a class of [graphene-]analogous, two-dimensional sheets made from a mix of carbon and nitrogen that are here to complement the one property that the wonder material graphene has not: a useful electronic band gap.” – Dr Mara Staffilani

MaterialsViews 2016. [Link]

macp.201500312

Highlight for the article: Bojdys,* M. J. Macromolecular Chemistry and Physics 2016, 217, 232–241. [DOI: 10.1002/macp.201500312]

Bojdys Group