Twinned Growth of Metal-Free, Triazine-Based Photocatalyst Films as Mixed-Dimensional (2D/3D) van der Waals Heterostructures.
basic_science · Level V
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- Record sourced from PubMed, PMID 28859235.
- Also identified by DOI 10.1002/adma.201703399.
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Abstract
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 (C<sub>3</sub> N<sub>3</sub> ) linkers grow as large area, transparent yellow-orange membranes on copper surfaces from solution. The membranes have an indirect band gap (E<sub>g,opt</sub> = 1.91 eV, E<sub>g,elec</sub> = 1.84 eV) and are moderately porous (124 m<sup>2</sup> g<sup>-1</sup> ). The material consists of a crystalline 2D phase that is fully sp<sup>2</sup> hybridized and provides structural stability, and an amorphous, porous phase with mixed sp<sup>2</sup> -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<sup>-1</sup> g<sup>-1</sup> 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.