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

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 (E-g,E-opt = 1.91 eV, E-g,E-elec = 1.84 eV) and are moderately porous (124 m(2) g(-1)). The material consists of a crystalline 2D phase that is fully sp(2) hybridized and provides structural stability, and an amorphous, porous phase with mixed sp(2)-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 mu mol 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.