Yize Zhang

Covalent triazine frameworks (CTFs) with donor–acceptor motifs have been identified as prospective semiconducting materials for photocatalysis. Though donor–acceptor motifs can favor forward intramolecular charge separation, some cases still suffer from backward charge recombination, resulting in the decrease of the photocatalytic activity. Herein, acetylene-bridged CTFs bearing an extended donor−π–acceptor motif was fabricated to prompt exciton dissociation. Experimental investigations and density functional theory calculations prove that the acetylene moiety can suppress backward charge recombination, minimize exciton binding energy, and enhance charge carrier lifetime, thereby prompting forward charge transfer/separation in comparison to the analogous one without acetylene. Thus, the acetylene-bridged CTFs showcased a higher photocatalytic activity for metal-free photocatalytic oxidative amines coupling with oxygen under visible-light irradiation, and apparent quantum efficiency at 420 nm was achieved up to 32.3%, that is, twofold higher than the one without acetylene. Furthermore, the acetylene moieties can adsorb oxygen molecules and provide active sites to lower the energy barrier and thus significantly enable the photoredox catalysis. This work provides alternative insights into the design and construction of high-performance CTFs, with prospective applications in solar-to-chemical energy conversion.

Abstract Photocatalytic CO 2 conversion into value‐added chemicals is a promising route but remains challenging due to poor product selectivity. Covalent organic frameworks (COFs) as an emerging class of porous materials are considered as promising candidates for photocatalysis. Incorporating metallic sites into COF is a successful strategy to realize high photocatalytic activities. Herein, 2,2′‐bipyridine‐based COF bearing non‐noble single Cu sites is fabricated by chelating coordination of dipyridyl units for photocatalytic CO 2 reduction. The coordinated single Cu sites not only significantly enhance light harvesting and accelerate electron–hole separation but also provide adsorption and activation sites for CO 2 molecules. As a proof of concept, the Cu‐Bpy‐COF as a representative catalyst exhibits superior photocatalytic activity for reducing CO 2 to CO and CH 4 without photosensitizer, and impressively, the product selectivity of CO and CH 4 can be readily modulated only by changing reaction media. Experimental and theoretical results reveal the crucial role of single Cu sites in promoting photoinduced charge separation and solvent effect in regulating product selectivity, which provides an important sight onto the design of COF photocatalysts for selective CO 2 photoreduction.

Covalent organic frameworks (COFs) are appealing platforms for photocatalysts because of their structural diversity and adjustable optical band gaps. The construction of efficient COFs for heterogeneous photocatalysis of organic transformations is highly desirable. Herein, we constructed a photoactive COF containing benzothiadiazole and triazine (BTDA-TAPT), for which the morphology and crystallinity might be easily tuned by slight synthetic variation. To unveil the relationship of photocatalytic properties between the structure and morphology, analogous COFs were synthesized by precisely tailoring building blocks. Systematic investigations indicated that tuning the structure and morphology might greatly impact photoelectric properties. The BTDA-TAPT featuring ordered alignment and perfect crystalline nature was more beneficial for promoting charge transfer and separation, which exhibited superior photocatalytic activity for visible light-driven oxidative coupling of amines. Outcomes from this study reveal the intrinsic synergy effects between the structure and morphology of COFs for photocatalysis.

Abstract Covalent organic framework (COF) has attracted increasing interest in photocatalytic CO 2 reduction, but it remains a challenge to achieve high conversion efficiency owing to the insufficient active site and fast charge recombination. Rationally optimizing the electronic structures of COF to regulate the local charge of active sites precisely is the key point to improving catalytic performance. Herein, intercalated single Co sites coordinated by imine‐N motifs have been designed by using trinuclear copper‐based imine‐COFs with distinct electronic moieties via a molecular engineering strategy. It is confirmed that the charge delivery property and local charge distribution of these heterometallic frameworks can be profoundly influenced by electronic structures. Among these featured structures with mixed‐state copper clusters, Co/Cu 3 ‐TPA‐COF stands out for an exceptional photocatalytic CO 2 reduction activity and tunable syngas (CO/H 2 ) ratio by changing various bipyridines. Experimental and theoretical results indicate that interlayer Co‐imine N motifs on the donor 1 ‐acceptor‐donor 2 structures facilitate the formation of a highly separated electron‐hole state, which effectively induces the oriented electron transfer from dual electron donors to Co centers, achieving an enhanced CO 2 activation and reduction. This work opens up an avenue for the design of high‐performance COF‐based catalysts for photocatalytic CO 2 reduction.