Forming electron traps deactivates self-assembled crystalline organic nanosheets toward photocatalytic overall water splitting

A High Crystalline Perylene-Based Hydrogen-Bonded Organic Framework for Enhanced Photocatalytic H2O2 Evolution

Hydrogen-bonded organic frameworks (HOFs) are a kind of crystalline porous material that have shown great potential for photocatalysis on account of their mild synthesis conditions and high crystallinity. Perylene-based photocatalysts have great potential for photocatalytic H2O2 production due to their excellent photochemical stability and broad spectral absorption. In this work, we designed and synthesized a high crystalline perylene-based HOF (PTBA) and an amorphous analog sample PTPA for photocatalytic H2O2 evolution. Under visible light irradiation, PTBA shows a higher photocatalytic H2O2 production rate of 2699 μmol g-1 h-1 than PTPA (2176 μmol g-1 h-1) and an apparent quantum yield (AQY) of 2.96% at 500 nm. The enhanced photocatalytic performance of PTBA is attributed to the promotion of the separation and transfer of photocarriers due to its high crystallinity. This work provides a precedent for the application of HOFs in the field of photocatalytic H2O2 generation.

Controlled Synthesis of Nitro-Terminated Oligothiophene/Crystallinity-Improved g-C3N4 Heterojunctions for Enhanced Visible-Light Catalytic H2 Production

It is highly desired to explore closely contacted polymer semiconductor/g-C₃N₄ heterojunction photocatalysts with promoted photogenerated-carrier separation and extended visible-light response for efficient visible-light-driven H₂ production. Here, we first synthesized the nitro-terminated oligothiophene (OTh) by the controlled copolymerization of thiophene and 2-nitrothiophene monomers, then constructed the nitro-terminated oligothiophene/crystallinity-improved g-C₃N₄ (OTh/g-C₃N₄) heterojunctions by a grinding-induced combination strategy. The ratio-optimized 20OTh₅/g-C₃N₄ shows highly efficient H₂ production activity up to 3.63 mmol h^-1 g^-1 under visible-light irradiation, with ∼25.9-time enhancement compared to that of g-C₃N₄. As verified by time-resolved photoluminescence spectra, surface photovoltage spectra, and the fluorescence spectra related to •OH amounts, the improved photocatalytic activity is due to the promoted photogenerated-carrier transfer and separation in the heterojunctions and the expanded visible-light response. It is also confirmed that the controlled OTh chain length, improved g-C₃N₄ crystallinity, and tight interface contact dependent on the hydrogen bonds and N···S interactions between OTh and g-C₃N₄ are reasonable for enhanced photogenerated-carrier separation with the electron transfer from OTh to g-C₃N₄. This work illustrates a feasible strategy to construct efficient polymer semiconductor/g-C₃N₄ heterojunction photocatalysts for solar-light-driven H₂ production.

Periodically nanoporous hydrogen-bonded organic frameworks for high performance photocatalysis

The development of highly catalytic hydrogen-bonded organic frameworks (HOFs) is of great importance, but remains challenging. Herein, we demonstrate the fabrication of a periodically nanoporous HOF for high performance photocatalysis. Compared with the conventional microporous HOFs, the nanoporous HOF architecture has a larger number of free carboxyl groups on the surface and presents greatly improved photoelectrochemical properties. It exhibits high catalytic activity for the photo-oxidative coupling of amines under mild conditions such as air atmosphere and room temperature and without any co-catalysts, sacrificial reagents or photosensitizers. The relationship between the structure, properties and catalytic performance of the nanoporous HOF was studied by experimental and theoretical investigations. It shows that such a HOF structure facilitates reactant adsorption and O₂ dissociation, thus promoting the oxidative coupling reaction. This work provides a new way for improving the catalytic performance of a single HOF.

Unveiling the Synthetic Potential of 1,3,5-Tri(10H-phenothiazin-10-yl)benzene-Based Optoelectronic Material: A Metal-Free and Recyclable Photocatalyst for Sequential Functionalization of C(sp2)-H Bonds

1,3,5-Tri(10H-phenothiazin-10-yl)benzene (3PTZ) is endowed with unique redox and photoresponsive characteristics and has been utilized as a p-type redox center for organic battery cathode material and a room-temperature phosphorescence (RTP) material, respectively. Conversely, its exploration in other research fields, particularly organic synthesis, remains unknown. Here, we demonstrate that 3PTZ-POP synthesized via cross-linking of 3PTZ is capable of harvesting visible-light photons and selectively converting solar energy to chemical energy. Specifically, 3PTZ-POP functions as a metal-free and recyclable photocatalyst to promote the sequential C(sp²)-H functionalizations of N-arylacrylamides with readily available trifluoromethylsulfonyl chloride as the radical precursor. An array of 3,3-disubstituted 2-oxindoles bearing a pharmaceutically important CF₃ moiety are delivered in moderate to excellent yields under mild and sustainable conditions.

Semiconducting Polymers for Oxygen Evolution Reaction under Light Illumination

Sunlight-driven water splitting to produce hydrogen fuel has stimulated intensive scientific interest, as this technology has the potential to revolutionize fossil fuel-based energy systems in modern society. The oxygen evolution reaction (OER) determines the performance of overall water splitting owing to its sluggish kinetics with multielectron transfer processing. Polymeric photocatalysts have recently been developed for the OER, and substantial progress has been realized in this emerging research field. In this Review, the focus is on the photocatalytic technologies and materials of polymeric photocatalysts for the OER. Two practical systems, namely, particle suspension systems and film-based photoelectrochemical systems, form two main sections. The concept is reviewed in terms of thermodynamics and kinetics, and polymeric photocatalysts are discussed based on three key characteristics, namely, light absorption, charge separation and transfer, and surface oxidation reactions. A satisfactory OER performance by polymeric photocatalysts will eventually offer a platform to achieve overall water splitting and other advanced applications in a cost-effective, sustainable, and renewable manner using solar energy.

Rational Design of Covalent Heptazine Frameworks with Spatially Separated Redox Centers for High-Efficiency Photocatalytic Hydrogen Peroxide Production

The redox reaction centers in natural organisms conducting oxygenic photosynthesis are well arranged in a physically separated manner to convert sunlight into chemical energy efficiently. Mimicking natural photosynthesis via precisely constructing oxidative and reductive reaction centers within photocatalysts is ideal for enhancing catalytic performances in artificial photosynthesis. In this study, new covalent heptazine frameworks (CHFs) with spatially separated redox centers are rationally designed for photocatalytic production of H₂ O₂ from water and oxygen without using any sacrificial agents. Both experimental and computational investigations indicate that the two-electron oxygen reduction reaction occurs on the heptazine moiety, whereas the two-electron water oxidation reaction occurs on the acetylene or diacetylene bond in the CHFs. This unique spatial separation feature is critical for enhancing charge separation and achieving efficient H₂ O₂ production. Meanwhile, the measured exciton binding energy of the diacetylene-containing polymer is merely 24 meV. Under simulated solar irradiation, the rationally designed CHFs can achieve a solar-to-chemical conversion efficiency of 0.78%, surpassing previously reported photocatalytic materials. This study establishes a molecular engineering approach to construct periodically arranged and spatially separated redox centers in single-component polymer photocatalysts, representing a hallmark to create more exciting polymer structures for photocatalysis moving forward.