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Hydrogen peroxide (H 2 O 2 ) is an important green oxidizing agent for environmental protection and chemical production. In comparison to the traditional anthraquinone method, photosynthesis is a green and energy-saving process for H 2 O 2 production. To improve the stability and practical application value of the H 2 O 2 synthesized by photocatalysis, the H 2 O 2 photosynthesis should be conducted in pure water without involving any sacrificial reagents. In this regard, organic semiconducting catalysts pose as a suitable candidate for photocatalytic H 2 O 2 synthesis owing to their metal-free nature to prevent H 2 O 2 decomposition by the metal ions. In this Perspective, the H 2 O 2 photosynthesis history is firstly introduced, followed by a review of the organic semiconductor photocatalysts reported to date. Finally, the main problems to thwart the advances of current pure H 2 O-to-H 2 O 2 photosynthesis are discussed, followed by proposed solutions to address these issues in order to pave new ways for the development of highly efficient metal-free organic photocatalysts for sustainable pure H 2 O-to-H 2 O 2 conversion., (© 2022 The Authors. ChemSusChem published by Wiley-VCH GmbH.)

Synthesizing H 2 O 2 from water and air via a photocatalytic approach is ideal for efficient production of this chemical at small-scale. However, the poor activity and selectivity of the 2 e - water oxidation reaction (WOR) greatly restricts the efficiency of photocatalytic H 2 O 2 production. Herein we prepare a bipyridine-based covalent organic framework photocatalyst (denoted as COF-TfpBpy) for H 2 O 2 production from water and air. The solar-to-chemical conversion (SCC) efficiency at 298 K and 333 K is 0.57 % and 1.08 %, respectively, which are higher than the current reported highest value. The resulting H 2 O 2 solution is capable of degrading pollutants. A mechanistic study revealed that the excellent photocatalytic activity of COF-TfpBpy is due to the protonation of bipyridine monomer, which promotes the rate-determining reaction (2 e - WOR) and then enhances Yeager-type oxygen adsorption to accelerate 2 e - one-step oxygen reduction. This work demonstrates, for the first time, the COF-catalyzed photosynthesis of H 2 O 2 from water and air; and paves the way for wastewater treatment using photocatalytic H 2 O 2 solution., (© 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

The synthesis of hydrogen peroxide through artificial photosynthesis is a green and promising technology with advantages in sustainability, economy and safety. However, superoxide radical (⋅O2−), an important intermediate in photocatalytic oxygen reduction to H2O2 production, has strong oxidizing properties that potentially destabilize the catalyst. Therefore, avoiding the accumulation of ⋅O2− for its rapid conversion to H2O2 is of paramount significance in improving catalyst stability and H2O2 yield. In this work, a strategy was developed to utilize protonated groups for the rapid depletion of converted ⋅O2−, thereby the efficiency of photocatalytic synthesis of H2O2 from CN was successfully enhanced by 47‐fold. The experimental findings demonstrated that polydopamine not only improved carrier separation efficiency, and more importantly, provided the adsorption reduction active site for ⋅O2− for efficient H2O2 production. This work offers a versatile approach for synthesizing efficient and stable photocatalysts. [ABSTRACT FROM AUTHOR]

With a view to using solar energy, the exploitation of near‐infrared (NIR) light, which constitutes about 50 % of solar energy, in photocatalytic H2O2 synthesis remains challenging. In this study, resorcinol−formaldehyde (RF), which has a relatively low bandgap and high conductivity, is introduced for photothermal catalytic generation of H2O2 under ambient conditions. Owing to the promoted surface charge transfer rate under high temperature, the photosynthetic yield reaches roughly 2000 μm within 40 min under 400 mW cm−2 irradiation with a solar‐to‐chemical conversion (SCC) efficiency of up to 0.19 % at 338 K under ambient conditions, exceeding the rate of photocatalysis with a cooling system by a factor of about 2.5. Notably, the H2O2 produced by RF during photothermal process was formed via a two‐channel pathway, leading to the overall promotion of H2O2 formation. The resultant H2O2 can be applied in situ for pollutant removal. This work offers a sustainable and economical route for the efficient formation of H2O2. [ABSTRACT FROM AUTHOR]

Hydrogen peroxide (H2O2) is an important green oxidizing agent for environmental protection and chemical production. In comparison to the traditional anthraquinone method, photosynthesis is a green and energy‐saving process for H2O2 production. To improve the stability and practical application value of the H2O2 synthesized by photocatalysis, the H2O2 photosynthesis should be conducted in pure water without involving any sacrificial reagents. In this regard, organic semiconducting catalysts pose as a suitable candidate for photocatalytic H2O2 synthesis owing to their metal‐free nature to prevent H2O2 decomposition by the metal ions. In this Perspective, the H2O2 photosynthesis history is firstly introduced, followed by a review of the organic semiconductor photocatalysts reported to date. Finally, the main problems to thwart the advances of current pure H2O‐to‐H2O2 photosynthesis are discussed, followed by proposed solutions to address these issues in order to pave new ways for the development of highly efficient metal‐free organic photocatalysts for sustainable pure H2O‐to‐H2O2 conversion. [ABSTRACT FROM AUTHOR]

K atoms are successfully introduced into the interlayers of g-C 3 N 4 frameworks. Taking advantage of the K–N bridge and the hollow structure, enhanced separation of photogenerated electrons and holes is achieved on K 10-TCN, which facilitates efficient photocatalytic H 2 and H 2 O 2 production. [Display omitted] • K atoms are successfully introduced into the interlayers of g-C 3 N 4 frameworks. • K–N coordination serves as an interlayer bridge between adjacent layers. • The synergistic effect of K–N bridge and hollow structure promotes carrier separation. • K 10-TCN exhibits superior activity for producing both H 2 and H 2 O 2. The development of bifunctional photocatalysts for enhancing hydrogen (H 2) and hydrogen peroxide (H 2 O 2) production from water is essential in addressing environmental and energy issues. However, the practical implementation of photocatalytic technology is still constrained by the inadequate separation of photo-generated charge carriers. Herein, potassium (K) atoms are introduced into the interlayers of graphitic carbon nitride (g-C 3 N 4) with a hollow hexagonal structure (K-TCN) and are coordinated with N atoms in adjacent layers. The presence of K–N coordination serves as a layer bridge, facilitating the separation of charge carriers. The hollow hexagonal structure reduces the distance over which photogenerated electrons migrate to the surface, thereby enhancing the reaction kinetics. Consequently, the optimized K-TCN exhibits a dramatically improved photocatalytic H 2 (941.6 μmol g−1h−1 with platinum (Pt) as the cocatalyst) and H 2 O 2 (347.6 μmol g−1h−1) generation as compared to hollow g-C 3 N 4 (TCN) and bulk g-C 3 N 4 nanosheet (CN) without K–N bridge under visible light irradiation. The unique design holds promising potential for developing highly efficient bifunctional photocatalysts towards producing renewable fuels and value-added chemicals. [ABSTRACT FROM AUTHOR]

Solar-driven photocatalytic H 2 O 2 production is a sustainable and clean technique with respect to the traditional route. Here, the efficient H 2 O 2 generation was accomplished by π−π coupling of AQ onto the few-layered graphitic carbon nitride (g-C 3 N 4) nanoplates through one-step mechanochemical treatment. A H 2 O 2 generation rate of 231 μM h−1 was obtained using AQ-coupled g-C 3 N 4 nanoplates under visible light illumination, exceeding that of the g-C 3 N 4 nanoplates and bulk g-C 3 N 4 by 7-time and 14-time, respectively. Experimental results showed that the high oxygen reduction efficiency could be ascribed to the enhanced surface area, more exposed active sites and the distinct AQ roles of the electrons storage and restraining the charge recombination. This work inspired future work in synthesizing H 2 O 2 through a sustainable and green route. g-C 3 N 4 nanoplates loaded redox molecules were synthesized through a scalable ball milling method. Few-layered structure and AQ coupling can boost the charge separation, offer more active sites and form a more reliable reduction medium (H 2 AQ). [Display omitted] • AQ-coupled g-C 3 N 4 nanoplates were prepared by one-step mechanochemical exfoliation. • The product retained the basic structure and optical properties of g-C 3 N 4 and is fully characterized. • The product showed photocatalytic H 2 O 2 production 14 times better than the bulk in the visible region. • The few-layered structure and AQ coupling led to boosted charge separation, more active sites and reliable reduction medium. [ABSTRACT FROM AUTHOR]

[Display omitted] • Regulating the proton demand–supply offers a fresh view on improving H 2 O 2 yield. • This work delves into effect of PCHA on H 2 O 2 production increased by 29 times. • The photomechanism was proposed based on a series of tests such as DIRFTS. • The proton regulation route by coating PCHA was applicable to other photocatalysts. In the H 2 O 2 photosynthesis, apart from the charge separation, the balance of proton supply and demand was also required between the kinetically faster oxygen reduction reaction (ORR) (μs ∼ ms) and the sluggish kinetics of water oxidation reaction (WOR) (s). Faced by this challenge, the article designed the heterojunction photocatalyst formed by in-situ polymerization of polyphenol amine on the surface of CdS under alkaline conditions. As a result, the synthesized CdS-Poly(catechol-hexamethylenediamine) (PCHA) produced 6.1 mM H 2 O 2 after 8 h of visible light irradiation, which is 29 times that of CdS. The experimental results evidenced that the coating of PCHA increased the charge separation and mobility, inhibited the photocorrosion of CdS, and thus enhanced the stability and photoactivity. Moreover, the catechol units of PCHA could function as a proton supplier and regulate local protons concentrations around the catalytic active sites to balance the proton supply–demand in the ORR and WOR at different reaction time scales. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ultrathin graphitic carbon nitride (g-C3N4) nanosheets were prepared by the glucose assisted exfoliation of the bulk g-C3N4. • The product retained the basic structure and optical properties of g-C3N4 and is fully characterized. • The product showed excellent photocatalytic performance in the visible region, which was 4 times better than the bulk. • The introduction of ultrathin structure changed the H2O2 generation pathway from a two-step single-electron reduction to a one-step two-electron reduction. Photocatalytic generation of hydrogen peroxide (H 2 O 2) is a sustainable technique to realize the solar-energy conversion. Here, ultrathin graphitic carbon nitride (g-C 3 N 4) nanoplates with thickness of 1–3 nm was introduced for the efficient H 2 O 2 production. The as-obtained nanoplates demonstrated the H 2 O 2 production rate of 43.07 μmol g−1 h−1 and about 4 times as high as the pristine g-C 3 N 4. Experimental results reflected that the ultrathin morphology offered an increased surface area, more active sites, smaller charge transfer length and stronger redox ability than that of the bulk counterparts. Moreover, the introduction of ultrathin structure switched the H 2 O 2 production pathway from a two-step single-electron reduction to a one-step two-electron reduction route. This study offered the deep elucidation of the influence of ultrathin structure on the photoactivity of semiconductor photocatalysts. [ABSTRACT FROM AUTHOR]