Visible light driven hydrogen (H2) production from water is a promising strategy to convert and store solar energy as chemical energy. Covalent organic frameworks (COFs) are front runners among different classes of organic photocatalyst, owing to their tunable porosity, crystallinity, optical and electronic properties.Photocatalytic activity of COFs depends on numerous factors such as band gap, crystallinity, porosity, exciton migration, charge separation and transport, stability etc. However, it is challenging to fine tune all these factors simultaneously to enhance the photocatalytic activity. Hence, in this report, we have prioritized the key factors for efficient photocatalytic H2 production through structure-property-activity relationship combined with microwave spectroscopy and first-principles calculations. Careful molecular engineering allowed us to tune the light absorption (i.e. band gap), crystallinity, porosity, layer stacking and charge carrier generation and transport of a series of isoreticular COFs. We have assessed how these properties and the interplay between them impact photocatalytic activity of studied COFs. From the structure-property-activity relationship, we found that light absorption and charge carrier generation and transport are the prime factors, which influence the photocatalytic H2 production of COFs in much greater extent than other factors. File list (2)download file view on ChemRxiv Ghosh_etal_Manuscript.pdf (5.34 MiB) download file view on ChemRxiv Ghosh_etal_SI.pdf (4.80 MiB) Scheme 1. Chemical structures of the building blocks along with corresponding molecular lengths and torsional angles. Reaction scheme for the synthesis of COFs under different solvothermal conditions, condition A and condition B.

In an aqueous solution, photophysical, photochemical, and photocatalytic abilities of a Ru(II)-Re(I) binuclear complex (RuReCl), of which Ru(II) photosensitizer and Re(I) catalyst units were connected with a bridging ligand, have been investigated in details. RuReCl could photocatalyze CO2 reduction using ascorbate as an electron donor, even in an aqueous solution. The main product of the photocatalytic reaction was formic acid in the aqueous solution; this is very different in product distribution from that in a dimethylformamide (DMF) and triethanolamine (TEOA) mixed solution in which the main product was CO. A (13)CO2 labeling experiment clearly showed that formic acid was produced from CO2. The turnover number and selectivity of the formic acid production were 25 and 83%, respectively. The quantum yield of the formic acid formation was 0.2%, which was much lower, compared to that in the DMF-TEOA mixed solution. Detail studies of the photochemical electron-transfer process showed back-electron transfer from the one-electron-reduced species (OERS) of the photosensitizer unit to an oxidized ascorbate efficiently proceeded, and this should be one of the main reasons why the photocatalytic efficiency was lower in the aqueous solution. In the aqueous solution, ligand substitution of the Ru(II) photosensitizer unit proceeded during the photocatalytic reaction, which was a main deactivation process of the photocatalytic reaction. The product of the ligand substitution was a Ru(II) bisdiimine complex or complexes with ascorbate as a ligand or ligands.

Tantalum and nitrogen co-doped rutile TiO2 nanorods were developed as a visible-light-active water oxidation photocatalyst for solar-driven Z-scheme water splitting.

The discovery of building blocks offers new opportunities to develop and control properties of extended solids. Compounds with fluorite-type Bi 2 O 2 blocks host various properties including lead-free ferroelectrics and photocatalysts. In this study, we show that triple-layered Bi 2 MO 4 blocks (M = Bi, La, Y) in Bi 2 MO 4 Cl allow, unlike double-layered Bi 2 O 2 blocks, to extensively control the conduction band. Depending on M, the Bi 2 MO 4 block is truncated by Bi−O bond breaking, resulting in a series of n-zigzag chain structures (n = 1, 2, ∞ for M = Bi, La, Y, respectively). Thus, formed chain structures are responsible for the variation in the conduction band minimum (−0.36 to −0.94 V vs SHE), which is correlated to the presence or absence of mirror symmetry at Bi. Bi 2 YO 4 Cl shows higher photoconductivity than the most efficient Bi 2 O 2 -based photocatalyst with promising visible-light photocatalytic activity for water splitting. This study expands the possibilities of thickening (2D to 3D) and cutting (2D to 1D) fluorite-based blocks toward desired photocatalysis and other functions.