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Benefiting from the excellent structural tunability, robust framework, ultrahigh porosity, and rich active sites, covalent organic frameworks (COFs) are widely recognized as promising photocatalysts in chemical conversions, and emerged in the hydrogen peroxide (H2O2) photosynthesis in 2020. H2O2, serving as an environmental‐friendly oxidant and a promising liquid fuel, has attracted increasing researchers to explore its potential. Over the past few years, numerous COFs‐based photocatalysts are developed with encouraging achievements in H2O2 production, whereas no comprehensive review articles exist to summarize this specific and significant area. Herein we provide a systematic overview of the advances and challenges of COFs in photocatalytic H2O2 production. We first introduce the priorities of COFs in H2O2 photosynthesis. Then, various strategies to improve COFs photocatalytic efficiency are discussed. The perspective and outlook for future advances of COFs in this emerging field are finally offered. This timely review will pave the way for the development of highly efficient COFs photocatalysts for practical production of value‐added chemicals not limited to H2O2. [ABSTRACT FROM AUTHOR]

In our study, we aimed to show how different reaction parameters can affect production rates using photocatalytic hydrogen peroxide formation by different polymeric carbon nitrides (PCN). For this purpose, selected materials were first compared under the same reaction conditions and compared with TiO2 (P25). We also show that different light intensities can have a different influence on seemingly similar materials. Since hydrogen peroxide production in the presence of an electron donor proceeds mainly by reduction of oxygen, we also show an influence of the oxygen flow on the formation rates. Thus, with high oxygen fluxes and high intensities of irradiated light, we were able to achieve an H2O2 concentration of 125 mM after about 25 h. Finally, the two best PCN materials were selected to measure light intensity dependence at different wavelengths up to visible light. It was found that they behaved differently at the different wavelengths and thus it could be shown that an exact specification of the reaction parameters is indispensable for comparisons in the literature. [ABSTRACT FROM AUTHOR]

The full reaction photosynthesis of H2O2 that can combine water‐oxidation and oxygen‐reduction without sacrificial agents is highly demanded to maximize the light‐utilization and overcome the complex reaction‐process of anthraquinone‐oxidation. Here, a kind of oxidation‐reduction molecular junction covalent‐organic‐framework (TTF‐BT‐COF) has been synthesized through the covalent‐coupling of tetrathiafulvalene (photo‐oxidation site) and benzothiazole (photo‐reduction site), which presents visible‐light‐adsorption region, effective electron‐hole separation‐efficiency and photo‐redox sites that enables full reaction generation of H2O2. Specifically, a record‐high yield (TTF‐BT‐COF, ≈276 000 μM h−1 g−1) for H2O2 photosynthesis without sacrificial agents has been achieved among porous crystalline photocatalysts. This is the first work that can design oxidation‐reduction molecular junction COFs for full reaction photosynthesis of H2O2, which might extend the scope of COFs in H2O2 production. [ABSTRACT FROM AUTHOR]

The full reaction photosynthesis of H2O2 that can combine water‐oxidation and oxygen‐reduction without sacrificial agents is highly demanded to maximize the light‐utilization and overcome the complex reaction‐process of anthraquinone‐oxidation. Here, a kind of oxidation‐reduction molecular junction covalent‐organic‐framework (TTF‐BT‐COF) has been synthesized through the covalent‐coupling of tetrathiafulvalene (photo‐oxidation site) and benzothiazole (photo‐reduction site), which presents visible‐light‐adsorption region, effective electron‐hole separation‐efficiency and photo‐redox sites that enables full reaction generation of H2O2. Specifically, a record‐high yield (TTF‐BT‐COF, ≈276 000 μM h−1 g−1) for H2O2 photosynthesis without sacrificial agents has been achieved among porous crystalline photocatalysts. This is the first work that can design oxidation‐reduction molecular junction COFs for full reaction photosynthesis of H2O2, which might extend the scope of COFs in H2O2 production. [ABSTRACT FROM AUTHOR]

Photocatalytic H2O2 production is a prospective alternative to the traditional anthraquinone oxidation method for H2O2 production. Compared to well‐established inorganic counterparts, organic photocatalysts show greater promise owing to their structural diversity and functional tunability, but unfortunately suffer from limited activity at present. Here, a comonomer doping strategy is reported to tune the electronic structures of covalent triazine framework nanoshells by introducing strong electron‐withdrawing benzothiadiazole units into the conjugated networks. The product exhibits much enhanced charge separation as evidenced by multiple spectroscopic analyses. When investigated as the photocatalyst in aqueous solution, the best sample can enable an impressive H2O2 production rate of 1630 µmol g−1 h−1, which is approximately three times higher than that of the undoped sample and superior to most other inorganic and organic competitors. [ABSTRACT FROM AUTHOR]

Hydrogen peroxide (H2O2) has received increasing attention because it is not only a mild and environmentally friendly oxidant for organic synthesis and environmental remediation but also a promising new liquid fuel. The production of H2O2 by photocatalysis is a sustainable process, since it uses water and oxygen as the source materials and solar light as the energy. Encouraging processes have been developed in the last decade for the photocatalytic production of H2O2. In this Review we summarize research progress in the development of processes for the photocatalytic production of H2O2. After a brief introduction emphasizing the superiorities of the photocatalytic generation of H2O2, the basic principles of establishing an efficient photocatalytic system for generating H2O2 are discussed, highlighting the advanced photocatalysts used. This Review is concluded by a brief summary and outlook for future advances in this emerging research field. [ABSTRACT FROM AUTHOR]

Polymeric carbon nitride modified with selected heteroatom dopants was prepared and used as a model photocatalyst to identify and understand the key mechanisms required for efficient photoproduction of H2O2 via selective oxygen reduction reaction (ORR). The photochemical production of H2O2 was achieved at a millimolar level per hour under visible‐light irradiation along with 100 % apparent quantum yield (in 360–450 nm region) and 96 % selectivity in an electrochemical system (0.1 V vs. RHE). Spectroscopic analysis in spatiotemporal resolution and theoretical calculations revealed that the synergistic association of alkali and sulfur dopants in the polymeric matrix promoted the interlayer charge separation and polarization of trapped electrons for preferable oxygen capture and reduction in ORR kinetics. This work highlights the key features that are responsible for controlling the photocatalytic activity and selectivity toward the two‐electron ORR, which should be the basis of further development of solar H2O2 production. [ABSTRACT FROM AUTHOR]

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Defect engineering is crucial in tailoring photocatalytic efficiency, but it suffers from uncertainty in determining the vacancy type and in which type of the vacancy can better promote the photocatalytic efficiency. In this study, Bi2S3 nanorods with bismuth or sulfur vacancies were synthesized to investigate their distinct effects on the electronic structure, electron–hole separation characteristics, and near‐infrared (NIR)‐driven photocatalytic bacterial inactivation activity. Both bismuth and sulfur vacancies can enhance the light absorption ability of Bi2S3. However, the lifetime of photoinduced electrons is extended by bismuth vacancies but shortened by sulfur vacancies. Owing to these tendencies, Bi2S3 with Bi vacancies fully inactivated 7 log E. coli cells within 40 min of NIR irradiation, displaying better NIR‐driven photocatalytic bacterial inactivation efficiency than Bi2S3 with S vacancies. This study discloses the defect‐type‐dependent photocatalytic behaviors, providing new insights into designing highly efficient photocatalysts. Special defects: Bi2S3 nanorods with Bi or S vacancies were synthesized to investigate their effects on the electronic structure, electron–hole separation, and near‐infrared‐driven photocatalytic bacterial inactivation activity. Both bismuth and sulfur vacancies can enhance the light absorption ability of Bi2S3. This study discloses the defect‐type‐dependent photocatalytic behaviors, providing new insights into designing highly efficient photocatalysts. [ABSTRACT FROM AUTHOR]

Photocatalysis, which can directly convert solar energy into chemical energy and simultaneously accomplish solar energy conversion and storage objectives, is regarded as one of the most promising strategies to address the energy supply and environmental degradation issues. In recent decades, great efforts and encouraging achievements are performed in the field of semiconductor photocatalysts. Herein, this progress report summarizes the recent investigations and focuses on the advanced semiconductor-based nanocomposite materials and structures and the novel mechanisms for the photocatalytic solar-to-chemical energy conversion. It begins with discussing basic principles for the establishment of an efficient photocatalysis system and illustrating recent studies on improving the elementary processes of photocatalysis, i.e., photophysics and surface/interface chemistry. Then, it demonstrates how the fundamental principles are utilized to enhance the important energy-conversion-related reactions, such as light-driven water splitting, CO2 reduction, nitrogen fixation, organic photosynthesis, etc. Finally, the report concludes the topic on semiconductor-based nanocomposite photocatalysis along with identifying crucial issues in fundamental studies, challenges in large-scale industrializations, and perspectives in related research fields. [ABSTRACT FROM AUTHOR]

Gold nanoparticle-loaded rutile TiO2 with a bimodal size distribution around 10.6 nm and 2.3 nm (BM-Au/TiO2) was prepared by the deposition precipitation and chemical reduction (DP-CR) technique. Visible-light irradiation (λ>430 nm) of the BM-Au/TiO2 plasmonic photocatalyst yields 35 μ m H2O2 in aerated pure water at irradiation time ( tp)=1 h, and the H2O2 concentration increases to 640±60 μ m by the addition of 4 % HCOOH as a sacrificing electron donor. Further, a carbonate-modified surface BM-Au/TiO2 (BM-Au/TiO2-CO32−) generates a millimolar level of H2O2 at tp=1 h with a quantum efficiency ( Φ) of 5.4 % at λ=530 nm under the same conditions. The recycle experiments confirmed the stable performance of BM-Au/TiO2. [ABSTRACT FROM AUTHOR]

Light-driven generation of H2O2 only from water and molecular oxygen could be an ideal pathway for clean production of solar fuels. In this work, a mixed metal oxide/graphitic-C3N4 (MMO@C3N4) composite was synthesized as a dual-functional photocatalyst for both water oxidation and oxygen reduction to generate H2O2. The MMO was derived from a NiFe-layered double hydroxide (LDH) precursor for obtaining a high dispersion of metal oxides on the surface of the C3N4 matrix. The C3N4 is in the graphitic phase and the main crystalline phase in MMO is cubic NiO. The XPS analyses revealed the doping of Fe3+ in the dominant NiO phase and the existence of surface defects in the C3N4 matrix. The formation and decomposition kinetics of H2O2 on the MMO@C3N4 and the control samples, including bare MMO, C3N4 matrix, Ni- or Fe-loaded C3N4 and a simple mixture of MMO and C3N4, were investigated. The MMO@C3N4 composite produced 63 μmol L−1 of H2O2 in 90 min in acidic solution (pH 3) and exhibited a significantly higher rate of production for H2O2 relative to the control samples. The positive shift of the valence band in the composite and the enhanced water oxidation catalysis by incorporating the MMO improved the light-induced hole collection relative to the bare C3N4 and resulted in the enhanced H2O2 formation. The positively shifted conduction band in the composite also improved the selectivity of the two-electron reduction of molecular oxygen to H2O2. [ABSTRACT FROM AUTHOR]