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Crystalline covalent organic frameworks (COFs) are porous polymeric semiconductors with network topologies, which are built from the integration of selected organic blocks with covalent bond linkages. They have shown great promise for artificial photosynthesis, owing to broad light harvesting, high crystallinity, and high carrier mobility. This Minireview introduces state‐of‐the‐art COF photocatalysts based on different linkages and discusses the origin of photocatalytic activities for hydrogen evolution. Three typical COF photocatalysts, with linkages including imine (−C=N−), β‐ketoenamine (O=C−C=C−NH−), and vinylene (−C=C−), are discussed with a particular focus on the advancements in synthetic methodologies and structural design, as well as photoelectronic properties that are relevant to photocatalytic performance. The Minireview is expected to elucidate their structure–property relationships and the way to design photoactive COFs with enhanced performances. [ABSTRACT FROM AUTHOR]

Facile fabrication of nanocatalysts consisting of metal nanoparticles (NPs) anchored on a functional support is highly desirable, yet remains challenging. Covalent organic frameworks (COFs) provide an emerging materials platform for structural control and functional design. Here, a facile one‐pot in situ reduction approach is demonstrated for the encapsulation of small Pd NPs into the shell of COF‐derived hollow polyamine spheres (Pd@H‐PPA). In the one‐pot synthetic process, the nucleation and growth of Pd NPs in the cavities of the porous shell take place simultaneously with the reduction of imine linkages to secondary amine groups. Pd@H‐PPA shows a significantly enhanced catalytic activity and recyclability in the tandem dehydrogenation of ammonia borane and selective hydrogenation of nitroarenes through an adsorption–activation–reaction mechanism. The strong interactions of the secondary amine linkage with borane and nitroarene molecules afford a positive synergy to promote the catalytic reaction. Moreover, the hierarchical structure of Pd@H‐PPA allows the accessibility of active Pd NPs to reactants. [ABSTRACT FROM AUTHOR]

Photocatalytic CO2 reduction into carbonaceous feedstock chemicals is a promising renewable energy technology to convert solar energy and greenhouse gases into chemical fuels. Here, a covalent triazine‐based framework (CTF) is demonstrated as an efficient cocatalyst to reduce CO2 under visible‐light irradiation. The nitrogen‐rich triazine moieties in CTF contribute to CO2 adsorption, while the periodical pore structure of CTF favors the accommodation of CO2 and electron mediator. Immobilization of cobalt species onto CTF promotes the photocatalytic activity with a 44‐fold enhancement over pristine CTF and the optimal CO production rate of the obtained Co/CTFs was up to 50 μmol g−1 h−1. The results of solid‐state UV‐vis diffuse reflectance spectra (UV‐vis DRS), CO2 adsorption and electrochemical impedance spectroscopy (EIS) illustrated that the increased activity was ascribed to the enhanced CO2 capture capacity, improved absorption of visible‐light and facilitated the transfer of charge from CTF to CO2 molecules. The CTF not only serves as a substrate for active Co species, but also bridges the photosensitizer with cobalt catalytic sites for the efficient transfer of photoexcited electrons. This work highlights the capability and ease of fabricating covalent organic framework‐based photocatalytic systems that are potentially useful for energy‐conversion applications. [ABSTRACT FROM AUTHOR]

Abstract: MoS2 quantum dots (QDs)‐modified covalent triazine‐based framework (MoS2/CTF) composites are synthesized through an in situ photodeposition method. MoS2 QDs are well distributed and stabilized on the layers of CTFs by coordination of the frameworks to MoS2. The QDs–sheet interactions between MoS2 and CTFs facilitate interfacial charge transfer and separation. As a consequence, the composites exhibit outstanding photocatalytic activity and stability for hydrogen evolution under visible light irradiation (λ≥420 nm), that exceed those over pristine CTFs and MoS2‐modified g‐C3N4 (MoS2/g‐C3N4) composite, making them promising materials for solar energy conversion. [ABSTRACT FROM AUTHOR]

Covalent organic frameworks (COFs) with hollow structures hold great promise for developing new types of functional materials. Herein, we report a hollow spherical COF with a hierarchical shell, which serves as an effective precursor of B,N-codoped hierarchical hollow carbon spheres. Benefiting from the synergistic effects of hierarchical porosity, high surface area, and B,N-codoping, the as-synthesized carbon spheres show prospective utility as metal-free catalysts in nitroarene reduction. A mechanistic hypothesis is proposed based on theoretical and experimental studies. Boron atoms situated meta to pyridinic N atoms are identified to be the main catalytic active sites. The anti-aromaticity originating from the codoping of B and pyridinic N atoms, not charge distribution and deformation energy, is confirmed to play a pivotal role in the catalytic reaction. [ABSTRACT FROM AUTHOR]

[Display omitted] Covalent organic frameworks (COFs) are crystalline porous materials with enormous potential for realizing solar-driven CO 2 -to-fuel conversion, yet the sluggish transfer/separation of photoinduced electrons and holes remains a compelling challenge. Herein, a step (S)-scheme heterojunction photocatalyst (CuWO 4 -COF) was rationally fabricated by a thermal annealing method for boosting CO 2 conversion to CO. The optimal CuWO 4 /COF composite sample, integrating 10 wt% CuWO 4 with an olefin (C═C) linked COF (TTCOF), achieved a remarkable gas–solid phase CO yield as high as 7.17 ± 0.35 μmol g−1h−1 under visible light irradiation, which was significantly higher than the pure COF (1.6 ± 0.29 μmol g−1h−1). The enhanced CO 2 conversion rate could be attributable to the interface engineering effect and the formation of internal electric field (IEF) directing from TTCOF to CuWO 4 according to the theoretical calculation and experimental results, which also proves the electrons transfer from TTCOF to CuWO 4 upon hybridization. In addition, driven by the IEF, the photoinduced electrons can be steered from CuWO 4 to TTCOF under visible light irradiation as well-elucidated by in-situ irradiated X-ray photoelectron spectroscopy, verifying the S-scheme charge transfer pathway over CuWO 4 /COF composite heterojunctions, which greatly foster the photoreduction activity of CO 2. The preparation technique of the S-scheme heterojunction photocatalyst in this study provides a paradigmatic protocol for photocatalytic solar fuel generation. [ABSTRACT FROM AUTHOR]

Designing photocatalysts with well-defined structure-function relationships is imperative for propelling the progression of desired photocatalytic oxidation. Herein, the efficient conversion of solar energy to H 2 O 2 and subsequently to hydroxyl radicals (•OH) is achieved through a synergistic interplay between olefin linkage (-C C-) and spatially separated benzene-triazine dual reaction sites within covalent organic frameworks (COFs). The upgraded -C C- can increase the conjugation degree of COFs, which establishes an expanded superstructure for boosting charge separation/transfer and stability. This precise modulation renders more opportunities for the hot electrons to migrate to the benzene site for solar-to-H 2 O 2 generation, and to the triazine site for H 2 O 2 -to-•OH, separately. The optimized •OH generation pathway enables remarkable oxidation performances against recalcitrant organic pollutants, and pathogenic microorganisms under visible light irradiation. This work provides new insights for tuning the synergistic interactions of various building blocks within the COFs for the selective generation of highly reactive •OH for environmental remediation. [Display omitted] • COFs with decisive structure-function relationship was tailored for •OH production. • ‐C C- bridge enhances conjugation and thereof the e- transfer and stability. • Site-specific functions: benzene drives O 2 to H 2 O 2 , triazine activates H 2 O 2 to •OH. • The oxidation power was proceeded through CB-e- rather than VB-h+. [ABSTRACT FROM AUTHOR]