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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]

Monolayer Bi2MoO6 nanosheets have been successfully prepared for the first time via a bottom-top approach with surfactant assistance, and show 8 times higher activity than bulk Bi2MoO6 for the selective oxidation of benzyl alcohol. Ultrafast charge separation and more acid–base active sites on the monolayer nanosheets are considered to be responsible for the robust photoactivity. [ABSTRACT FROM AUTHOR]

Covalent triazine-based frameworks (CTFs) with a graphene-like layered morphology have been controllably synthesized by the trifluoromethanesulfonic acid-catalyzed nitrile trimerization reactions at room temperature via selecting different monomers. Platinum nanoparticles are well dispersed in CTF-T1, which is ascribed to the synergistic effects of the coordination of triazine moieties and the nanoscale confinement effect of CTFs. CTF-T1 exhibits excellent photocatalytic activity and stability for H2 evolution in the presence of platinum under visible light irradiation ( λ ≥ 420 nm). The activity and stability of CTF-T1 are comparable to those of g-C3N4. Importantly, as a result of the tailorable electronic and spatial structures of CTFs that can be achieved through the judicial selection of monomers, CTFs not only show great potential as organic semiconductor for photocatalysis but also may provide a molecular-level understanding of the inherent heterogeneous photocatalysis. [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]

Monolayer H 1.4 Ti 1.65 O 4 ·H 2 O nanosheet (denoted as NST) has been prepared as a photocatalyst for the oxidation of furfuryl alcohol (denoted as FA) to furaldehyde under visible light irradiation. The photocatalytic activity of NST is over 10 times higher than that of its layered counterpart. This enhanced activity may be attributed to the high percentage of exposed Lewis acid sites in NST. The in-situ FTIR result suggests that FA are efficiently chemosorbed on the exposed Lewis acid sites forming the surface coordination species via C O groups, resulting in the activation of FA. The surface coordination species would respond to visible light absorption. Furthermore, The XAFS result shows that the signals for Ti O and Ti–Ti in NST are weaker dramatically and the signals positions are shifted by 0.03 Å in the higher R direction as compared with those in layered counterpart, suggesting the more exposed Ti and O defects in NST. The oxygen molecules absorbed on these surface defects are activated forming O 2 − by photo-electrons under visible light irradiation. Finally, a possible mechanism has been proposed at a molecular level. [ABSTRACT FROM AUTHOR]