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

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 N ) linkers grow as large area, transparent yellow-orange membranes on copper surfaces from solution. The membranes have an indirect band gap (E = 1.91 eV, E = 1.84 eV) and are moderately porous (124 m g ). The material consists of a crystalline 2D phase that is fully sp hybridized and provides structural stability, and an amorphous, porous phase with mixed sp -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 g 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.

Tuning the Porosity and Photocatalytic Performance of Triazine‐Based Graphdiyne Polymers through Polymorphism

“…The addition of Pt has a markedly lower effect on TzG Cu . Here, improved interlayer packing leads to a relatively efficient electron transfer, with or without a cocatalyst, as shown previously for crystalline, conductive triazine films …”

“…X‐ray photoelectron spectroscopy (XPS) shows that TzG Cu retains some copper catalyst—0.85 wt % by energy‐dispersive X‐ray spectroscopy (EDX; Table S1) and up to 4.45 wt % by ICP‐OES (Table S2) and thermogravimetric analysis (TGA; Figure S2)—either as Cu metal, or as Cu I oxides (Figure j, Figure S3). The difference in copper content from both methods indicates that copper is embedded within the polymer matrix away from the external surfaces, and that it is unlikely to affect the photocatalytic activity and bulk properties of the polymer at such low quantities, as previously reported …”

“…Triazine is a particularly interesting structural motif for the design of organic polymer networks because it combines heteroatoms held in π‐conjugation and C 3 ‐symmetric co‐planarity . We have successfully used this D–A motif of TzG as part of a 2 D/3 D van der Waals heterostructure for noble metal‐free photocatalytic hydrogen evolution …”

“…The radical component of TzG Cu ( g factor 2.0032, linewidth 0.63 mT) is two times more intense than that of TzG Pd/Cu ( g factor 2.0035, linewidth 0.66 mT), indicating a higher concentration of induced polaron‐like centers in TzG Cu than in TzG Pd/Cu . The spectrum of TzG Cu shows in addition a feature between 340 mT and 345 mT that corresponds to paramagnetic Cu 2+ species . j) Argon sorption isotherms for TzG Pd/Cu (blue) and TzG Cu (black) measured at 87 K.…”

“…[9] We have successfully used this D-AmotifofTzG as part of a2D/3D vander Waalsheterostructure fornoble metal-free photocatalytic hydrogen evolution. [10] [a] Dr.…”