
==== Front
Nat Commun
Nat Commun
Nature Communications
2041-1723
Nature Publishing Group UK London

52405
10.1038/s41467-024-52405-3
Article
Perfluoroalkyl-modified covalent organic frameworks for continuous photocatalytic hydrogen peroxide synthesis and extraction in a biphasic fluid system
Shao Chaochen 12
Yu Xiaohan 12
http://orcid.org/0000-0003-3177-2073
Ji Yujin 12
http://orcid.org/0000-0002-4506-9701
Xu Jie 3
Yan Yuchen 12
Hu Yongpan 12
http://orcid.org/0000-0002-5248-2756
Li Youyong 12
http://orcid.org/0000-0003-3808-8258
Huang Wei weihuang@suda.edu.cn

12
http://orcid.org/0000-0003-0506-0451
Li Yanguang yanguang@suda.edu.cn

124
1 grid.263761.7 0000 0001 0198 0694 Institute of Functional Nano & Soft Materials (FUNSOM), Soochow University, 215123 Suzhou, China
2 https://ror.org/05kvm7n82 grid.445078.a 0000 0001 2290 4690 Jiangsu Key Laboratory of Advanced Negative Carbon Technologies, Soochow University, 215123 Suzhou, China
3 https://ror.org/020hxh324 grid.412899.f 0000 0000 9117 1462 College of Chemistry and Materials Engineering, Wenzhou University, 325035 Wenzhou, Zhejiang China
4 https://ror.org/03jqs2n27 grid.259384.1 0000 0000 8945 4455 Macao Institute of Materials Science and Engineering (MIMSE), MUST-SUDA Joint Research Center for Advanced Functional Materials, Macau University of Science and Technology, 999078 Macao, China
13 9 2024
13 9 2024
2024
15 802320 4 2024
5 9 2024
© The Author(s) 2024
2024
https://creativecommons.org/licenses/by-nc-nd/4.0/ Open Access This article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which permits any non-commercial use, sharing, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if you modified the licensed material. You do not have permission under this licence to share adapted material derived from this article or parts of it. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by-nc-nd/4.0/.
H2O2 photosynthesis represents an appealing approach for sustainable and decentralized H2O2 production. Unfortunately, current reactions are mostly carried out in laboratory-scale single-phase batch reactors, which have a limited H2O2 production rate (<100 μmol h−1) and cannot operate in an uninterrupted manner. Herein, we propose continuous H2O2 photosynthesis and extraction in a biphasic fluid system. A superhydrophobic covalent organic framework photocatalyst with perfluoroalkyl functionalization is rationally designed and prepared via the Schiff-base reaction. When applied in a home-built biphasic fluid photo-reactor, the superhydrophobicity of our photocatalyst allows its selective dispersion in the oil phase, while formed H2O2 is spontaneously extracted to the water phase. Through optimizing reaction parameters, we achieve continuous H2O2 photosynthesis and extraction with an unprecedented production rate of up to 968 μmol h−1 and tunable H2O2 concentrations from 2.2 to 38.1 mM. As-obtained H2O2 solution could satisfactorily meet the general demands of household disinfection and wastewater treatments.

Photocatalytic H2O2 synthesis is often performed in lab-scale batch reactors with low efficiency. Here, the authors report a biphasic fluid system that enables continuous H2O2 synthesis and automatic product extraction, addressing the limitations of traditional methods.

Subject terms

Organic-inorganic nanostructures
Photocatalysis
Catalysis
https://doi.org/10.13039/501100001809 National Natural Science Foundation of China (National Science Foundation of China) 52161160331 U2002213 Li Yanguang https://doi.org/10.13039/501100004608 Natural Science Foundation of Jiangsu Province (Jiangsu Provincial Natural Science Foundation) BK20220027 Li Yanguang Science and Technology Development Fund Macau SAR (0077/2021/A2) Natural Science Foundation of the Jiangsu Higher Education Institutions of China (20KJA430002)issue-copyright-statement© Springer Nature Limited 2024
==== Body
pmcIntroduction

Hydrogen peroxide (H2O2) is one of the most essential basic chemicals for synthetic industry, environmental remediation, and medical disinfection, with an annual global demand of 4.4 million tons and a market size of USD 3.2 billion in 20221,2. During the recent COVID-19 pandemic, its demand has risen substantially owing to its wide use in the formulation of disinfectant products3. At present, over 95% of commercial H2O2 is manufactured through the well-established anthraquinone oxidation process in centralized plants, involving substantial energy consumption and waste emission4. It generally yields highly concentrated H2O2, whose storage, transportation, and handling may pose significant safety risks. On many occasions, however, end-users only need dilute H2O2 solution: for example, <0.1 wt% (or ~30 mM) H2O2 is usually sufficient for water treatments and antibacterial purposes5,6. This notable gap between production and consumption stimulates us to search for alternative processes to enable the on-site, on-demand production of dilute H2O2 solution7,8.

Solar-driven H2O2 photosynthesis from oxygen and water has emerged as a promising route9–11. It uses solar energy as the sole energy input and generates no waste chemicals throughout the reaction process. Over recent years, a variety of photocatalysts have been developed with many exciting progresses12–15. They, unfortunately, have been predominantly investigated in laboratory-scale single-phase batch reactors, in which catalyst powders are dispersed in an O2-saturated aqueous solution (Fig. 1a)14,16. While such a batch configuration is easy to operate and permits quick catalyst screening, its often limited size (solution volume <50 mL) and H2O2 production rate (<100 μmol h−1) are far from amenable to practical applications17. Moreover, all the batch reactors only operate intermittently, and necessitate repetitive catalyst separation and recycling at intervals as short as a few hours to extract H2O2 solution, resulting in low productivity and added expenses. Several attempts have been made to address this limitation. For example, biphasic batch reactors containing liquid water and oil phases have been shown to facilitate the spontaneous separation and collection of H2O218,19. Supporting photocatalyst powders on porous hydrophobic substrates floating on the solution surface creates abundant triple-phase boundaries, and promotes O2 mass transfer and hence H2O2 production20,21. Despite some performance gains, none of them could enable the continuous photosynthesis and extraction of H2O2 at practically meaningful concentrations for directly connecting to the end users.Fig. 1 Schematic illustration of the reaction systems for photocatalytic H2O2 production.

a Previously reported photocatalytic systems for H2O2 production including the monophasic system, H2O-oil biphasic system, and gas-solid-liquid triphasic system. The colors yellow, blue, and pink represent the photocatalyst, water phase, and oil phase, respectively, while the gray grids denote the hydrophobic support. b Biphasic fluid system that enables continuous H2O2 photosynthesis, separation, and extraction. The colors yellow, blue, and pink represent the photocatalyst, water phase, and oil phase, respectively.

We envision that a biphasic fluid system represents a promising solution to the above challenge (Fig. 1b). Fluid reactors have the demonstrated potential for the continuous electrosynthesis or photosynthesis of a variety of valuable chemicals22–26. The introduction of biphasic water-oil reaction solution within fluid systems may benefit spontaneous H2O2 separation while being continuously produced. To achieve so, desirable photocatalyst materials should have strong surface hydrophobicity in order to be stably and selectively dispersed in organic phases. Covalent organic frameworks (COFs)—a class of crystalline and porous polymer semiconductors—are appealing candidates by virtue of their versatile structural diversity, and tunable optoelectronic and surface properties27–31. Their interactions with solvents could, in principle, be modified by incorporating proper functional building blocks32. Based on the above reasoning, we here prepare a superhydrophobic COF photocatalyst via a judiciously designed Schiff-base reaction between tritopic amine and tetratopic aldehyde monomers. Their symmetry mismatch leaves periodical uncondensed aldehyde sites, which are subsequently grafted with perfluoroalkyl chains to afford the product with superhydrophobicity. This surface property allows the photocatalyst to be stably dispersed in the oil phase within a biphasic fluid photo-reactor. By properly adjusting reaction parameters, we achieve continuous production and extraction of pure H2O2 solution with an exceptional production rate of up to 968 μmol h−1 and tunable H2O2 concentrations from 2.2 to 38.1 mM. As-prepared H2O2 solution can be used for household disinfection and environmental remediation.

Results

Preparation and characterizations of BTTA-COF and PF-BTTA-COF

As schematically illustrated in Fig. 2a, our catalyst was prepared through a [4+3] Schiff-base condensation reaction between 5,5’-(benzo[c][1,2,5]thiadiazole-4,7-diyl)diisophthalaldehyde (BTDIPA) and 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TAPT) under a solvothermal condition (see the synthetic details in the Supplementary Information). The as-prepared sample from this step is denoted as BTTA-COF. Previous studies indicated that benzothiadiazole (BT) and triazine moieties favored the two-electron oxygen reduction reaction (2e− ORR)33–35. Their abundant incorporation into polymeric frameworks is expected to accelerate H2O2 photosynthesis. Moreover, the symmetry mismatch between tritopic amines and tetratopic aldehydes leaves uncondensed aldehyde sites after the reaction, which could be subsequently functionalized with other molecules for regulating the photocatalyst surface wettability. Here in order to afford BTTA-COF with superhydrophobicity, its unreacted aldehyde sites were further condensed with 1H,1H-undecafluorohexylamine (UFHA) via the Schiff-base reaction. The final product is denoted as PF-BTTA-COF to reflect its perfluoroalkyl functionalization.Fig. 2 Syntheses, characterizations, and batch photocatalysis experiments of BTTA-COF and/or PF-BTTA-COF.

a Schematic synthetic procedure for BTTA-COF and PF-BTTA-COF. b FT-IR spectra of BTTA-COF, PF-BTTA-COF, and TAPT. c XRD patterns of BTTA-COF and PF-BTTA-COF. d TEM image of PF-BTTA-COF. e Water or α,α,α-trifluorotoluene (TFT) contact angle measurements of BTTA-COF and PF-BTTA-COF as well as the photograph showing their dispersion in biphasic H2O-TFT mixture. f Time-dependent H2O2 evolution on BTTA-COF within batch reactors of two different sizes while retaining the same catalyst concentration.

The molecular structures of both samples were interrogated by spectroscopic characterizations. In the Fourier-transform infrared (FT-IR) spectrum of BTTA-COF, the emergence of the signature imine signal at 1627 cm−1 attests to the successful condensation between monomers (Supplementary Fig. 1a)36. Its moderate signal at 1696 cm−1 indicates the existence of uncondensed aldehyde sites owing to the monomer symmetry mismatch as explained above, while no unreacted amine signal is noted in BTTA-COF (Fig. 2b)37,38. The molar percentage of residual aldehydes is estimated to be 15%, close to the theoretical value (Supplementary Fig. 2a–c). The subsequent introduction of perfluoroalkyl functionalities in PF-BTTA-COF does not disrupt the overall molecular structure (Supplementary Fig. 1b). New peaks, however, are observed at 1237 cm−1 and 1201 cm−1 assignable to the C-F bonding in PF-BTTA-COF, and the signal intensity of uncondensed aldehydes significantly attenuates after modification, evidencing that perfluoroalkyl groups are successfully grafted to the polymeric frameworks39. Energy-dispersive X-ray spectroscopy (EDS) analysis reveals a fluorine content of 5.3 wt%, indicating that around one-third of unreacted aldehydes are modified by UFHA (Supplementary Fig. 2d, e)40,41. The condensed molecular structure and incorporation of perfluoroalkane are also corroborated by the solid-state 13C (Supplementary Fig. 3a) and 19F nuclear magnetic resonance (NMR) results (Supplementary Fig. 3b).

Both BTTA-COF and PF-BTTA-COF feature great structural crystallinity. Their X-ray diffraction patterns (XRD) exhibit intense peaks that can be simulated by the eclipsed (AA) stacking of two-dimensional (2D) molecular layers (Fig. 2c and Supplementary Fig. 4). The strongest signal at 2θ = 6.1° corresponds to the (100) diffraction and evidences the in-plane ordering with a d-spacing of 14.4 Å—close to the pore-to-pore distance of the proposed structure (14 Å). N2 sorption isotherms reveal their microporous nature (Supplementary Fig. 5a). The Brunauer‐Emmett‐Teller (BET) specific surface area is calculated to be 1090 m2 g−1 for BTTA-COF and 462 m2 g−1 for PF-BTTA-COF, with an average pore size of 1.39 and 1.27 nm, respectively (Supplementary Fig. 5b). The decreased surface area and pore size of PF-BTTA-COF result from its pore filling with perfluoroalkane as expected. Furthermore, scanning electron microscopy (SEM) imaging shows the rod-like morphology of both samples (Supplementary Fig. 6). High-resolution transmission electron microscopy (TEM) imaging unveils clear lattice fringes and supports their long-range structural ordering (Fig. 2d and Supplementary Fig. 7). Thermogravimetric analysis (TGA) under N2 evidences the excellent thermal stability of both samples up to 500 °C (Supplementary Fig. 8).

Surface hydrophobicity is a prerequisite to the catalyst design for biphasic H2O2 photosynthesis18. To investigate the effect of perfluoroalkyl functionalization, water contact angle (CA) measurements were conducted. As shown in Fig. 2e, unmodified BTTA-COF exhibits a static water CA of 31.4°, while the CA value is dramatically increased to 151.2° for PF-BTTA-COF. When α,α,α-trifluorotoluene (TFT)—a commonly used water-immiscible organic solvent—is dropped onto the surface of PF-BTTA-COF, the organic solvent quickly spreads and is absorbed in less than a second. These results reflect the superhydrophobicity and superoleophilicity of PF-BTTA-COF as a result of perfluoroalkyl functionalization. Thanks to this unique surface property, when its powder is added to an immiscible H2O-TFT mixture, PF-BTTA-COF immediately migrates to and becomes stably dispersed in the oil phase, forming a clear oil-water boundary. Such a feature is essential to the continuous H2O2 production and extraction in our biphasic fluid system, as will be shown later. By sharp contrast, unmodified BTTA-COF does not form selective dispersion and can be suspended in both water and TFT.

We also examined the optoelectronic properties of our samples. The ultraviolet-visible (UV-Vis) diffuse reflectance spectrum of BTTA-COF displays an adsorption onset at 550 nm (Supplementary Fig. 9a). This corresponds to an optical band gap (Eg) of 2.58 eV according to the Tauc’s relation. Using Mott-Schottky and ultraviolet photoelectron spectroscopy (UPS) analyses, its conduction band (CB) and valence band (VB) positions are estimated to be −0.57 V and 2.01 V versus normal hydrogen electrode (NHE), respectively (Supplementary Fig. 9b, c). The incorporation of perfluoroalkyl groups in PF-BTTA-COF does not noticeably modify the optoelectronic property (Supplementary Fig. 10a–c). Based on their electronic structures, both samples are capable of driving simultaneous 2e− ORR and 4e− water oxidation reaction (4e− WOR) (Supplementary Figs. 9d and 10d).

Photocatalytic measurements of BTTA-COF in a batch system

In order to evaluate the potential of our photocatalysts and to make a fair comparison with other competitors under similar conditions, we first conducted photocatalytic measurements of hydrophilic BTTA-COF in a conventional single-phase batch reactor. The catalyst powder was dispersed in 10 mL of pure water at an optimal concentration of 1 g L−1 (Supplementary Figs. 11 and 12, see more photocatalysis details in the Supplementary Information). Under visible light irradiation (λ > 420 nm), BTTA-COF enables H2O2 production and linear accumulation over time, yielding a total amount of 53 μmol after 2 h (Fig. 2f). This corresponds to a H2O2 production rate of 2650 μmol h−1 g−1 or a concentration accumulation rate of 2.65 mM h−1. Control experiments show that H2O2 is predominantly produced through the 2e− ORR by photogenerated electrons (Supplementary Fig. 13a). This process involves the formation of both superoxide anion (•O2−) and endoperoxide (–O–O–) intermediates, as verified by electron paramagnetic resonance (EPR) and in-situ diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS) analyses (Supplementary Fig. 14), while photogenerated holes are responsible for driving the 4e− WOR to O2 (Supplementary Fig. 13b)26,42,43. Moreover, when benzyl alcohol (BA) is introduced as the sacrificial electron donor to accelerate hole consumption under otherwise identical conditions, the H2O2 production rate and concentration accumulation rate are further boosted to 5691 μmol h−1 g−1 and 5.69 mM h−1, respectively (Supplementary Fig. 15). The apparent quantum efficiency (AQE) at 420 nm is measured to be 18% in pure water (Supplementary Fig. 16a) and 37.4% in the presence of BA (Supplementary Fig. 16b). In addition, the solar-to-chemical energy conversion (SCC) efficiency is calculated to be 0.48% in pure water (Supplementary Fig. 17). All these metrics are comparable to other state-of-the-art candidates in pure water or aqueous solutions involving sacrificial electron donors under similar conditions (Supplementary Table 1)19,26,42–49.

BTTA-COF has the required stability for H2O2 photosynthesis in pure water. It shows great compatibility with H2O2, and does not catalyze H2O2 degradation even under visible light irradiation (Supplementary Fig. 18). The cycling photocatalytic experiment demonstrates a negligible activity loss after 6 reaction cycles and a total of 30 h (Supplementary Fig. 19). Characterizations of the catalyst retrieved after the cycling experiment reveal no discernable change in its structure or optoelectronic properties (Supplementary Fig. 20). Note that PF-BTTA-COF exhibits a comparable photocatalytic activity to BTTA-COF under identical reaction conditions, which is expected given their similar optoelectronic properties (Supplementary Fig. 21).

Despite their wide use in photocatalytic measurements, single-phase batch reactors are not amenable to practical applications owing to their limited solution volumes and intermittent operation. We attempted to address the first issue by enlarging the batch reactor and increasing the solution volume to 150 mL (15 times larger) while maintaining the same catalyst concentration and light illumination intensity. Unfortunately, the H2O2 yield does not proportionally increase: the total amount only increases 3 times in pure water, while the normalized H2O2 production rate and concentration accumulation rate are substantially lowered to 0.4 mM h−1 and 400 μmol h−1 g−1, respectively (Fig. 2f). This leads us to conclude that we cannot simply scale up the reaction in batch reactors owing to insufficient light penetration depth and catalyst utilization in large sized reactors50. More importantly, batch reactors are not suitable for continuous H2O2 production and extraction, which we aim for in this study.

Continuous H2O2 photosynthesis and extraction by PF-BTTA-COF in a biphasic fluid system

A biphasic fluid system was developed to address the unavoidable drawbacks of conventional batch reactors. It consists of three main components, as depicted by the photo in Fig. 3a. O2-saturated photocatalyst dispersion in an organic solvent and pure water are co-fed into a T-shaped mixer through peristaltic pumps at controlled flow rates. This generates a series of stable oil-water biphasic segments inside transparent tubular flow channels, which are subsequently transported into a coiled reactor (total channel length ~44 m) irradiated by a set of light-emitting diodes (λ = 455 nm, 25 mW cm−2). During the reaction, the small diameter (~1.6 mm) of flow channels reduces the light penetration path when side-irradiated; the presence of abundant biphasic oil-water interfaces promotes H2O2 extraction from the oil phase to the water phase (Fig. 3b). The oil/water segment lengths and density of the biphasic interfaces could be readily tuned by varying the relative liquid feeding rates (Fig. 3c). After passing through the coiled reactor, the H2O2 solution and photocatalyst dispersion are fed to a collector, where they spontaneously separate into two layers of liquids due to their immiscibility (Supplementary Fig. 22). The upper H2O2 solution is extracted for practical applications, while the lower photocatalyst dispersion is pumped back for subsequent use. Such a biphasic fluid system can continuously yield pure H2O2 solution with tunable concentrations.Fig. 3 Photocatalytic H2O2 production on PF-BTTA-COF in the biphasic fluid system.

a Photographs of the home-built biphasic fluid photocatalytic system in operation. Dashed squares highlight (i) the T-shape mixer for mixing water and oil flows and (ii) spontaneous product separation and collection. b Schematic illustration of H2O2 formation in TFT and migration across the oil-water interfaces. c Typical images of oil-water segments formed inside tubular flow channels at different flow rates and FW/FO ratios. d H2O2 production rate and average solution concentration from the biphasic fluid system at different flow rates (FW = FO). Error bars represent the standard deviations of three independent experiments. e H2O2 production rate and average solution concentration at different FW/FO ratios (FW + FO = 2.12 mL min−1). Error bars represent the standard deviations of three independent experiments. f Performance comparison of PF-BTTA-COF in our biphasic fluid system with those of other state-of-the-art photocatalysts in terms of H2O2 production rate and concentration. Open and filled circles represent the studies in pure water and in the presence of sacrificial electron donors, respectively.

We used superhydrophobic PF-BTTA-COF in the above-developed biphasic fluid system for continuous H2O2 production as a proof of concept. TFT was chosen as the organic solvent in our study considering its excellent wetting of PF-BTTA-COF, complete immiscibility with water, and high oxygen solubility51,52. Our catalyst powder was dispersed in TFT at a concentration of 2 g L−1. When the feeding rates of water (FW) and TFT (FO) are both set at 0.43 mL min−1 to start with, the catalyst retention time inside the coiled reactor is about 100 min, and our biphasic fluid system continuously produces pure H2O2 solution at a rate of 99 μmol h−1 (Supplementary Fig. 23). The introduction of BA in TFT as the sacrificial electron donor further enhances the H2O2 production rate to 318 μmol h−1 and yields H2O2 solution at a concentration of 12.2 mM. Note that BA and its oxidation product benzaldehyde have much higher solubility in TFT than in water, as evidenced by the 1H NMR analysis (Supplementary Fig. 24). This is essential for biphasic H2O2 photosynthesis. As a result, our following optimization is approached in the presence of BA.

We examined the effect of liquid flow rates on photocatalytic activities. Increasing the flow rates is expected to reduce the catalyst retention time in the coiled reactor, and therefore decrease the attainable H2O2 concentration. For example, when both FW and FO are increased to 0.71 mL min−1, the H2O2 concentration is lowered to 9.1 mM; it is further lowered to 6.1 or 3.1 mM at FW = FO = 1.08 or 2.02 mL min−1, respectively (Fig. 3d). Varying the overall flow rate while keeping FW = FO does not significantly change the H2O2 production rate (300 ~ 400 μmol h−1). This is because equal FW and FO values always result in equi-length water and oil segments in tubular flow channels and thereby similar light utilization efficiency. We also investigated the effect of the FW/FO ratio while keeping the same overall flow rate (2.12 mL min−1). At a large FW/FO ratio of 2, the H2O2 production rate is measured to be 363 μmol h−1, and the H2O2 concentration is 4.3 mM (Fig. 3e). Both values improve with decreasing FW/FO ratios due to the enhanced light utilization efficiency by the catalyst dispersed in oil. At the lowest FW/FO ratio of 1/4 (as limited by our peristaltic pumps), the H2O2 production rate and H2O2 concentration are measured to be 616 μmol h−1 and 24.3 mM, respectively. Furthermore, lowering the pH value of the water phase with dilute acid is found to promote H2O2 photosynthesis. For example, the H2O2 production rate of PF-BTTA-COF is boosted to 847 μmol h−1 at pH = 3 and the optimal flow rates, while alkaline pH adversely affects the performance owing to spontaneous H2O2 decomposition under the alkaline condition (Supplementary Fig. 25a)53. At last, rising the BA content in TFT to 50 vol% further enhances the H2O2 production rate and concentration to 968 μmol h−1 and 38.1 mM (0.13 wt%) respectively under the optimal flow rates and water pH (Supplementary Fig. 25b). To our best knowledge, such extraordinary H2O2 production rate is 1 ~ 2 order of magnitude greater than all earlier studies (10 ~ 100 μmol h−1) (Fig. 3f and Supplementary Table 1), thereby unambiguously underlining the unique advantage of our biphasic fluid system34,35,45,48,49,54–59.

We next carried out continuous H2O2 photosynthesis using our biphasic fluid system at FW = 1.04 mL min−1 and FO = 2.08 mL min−1. As shown in Fig. 4a, the total H2O2 amount linearly accumulates at the first 80 h, and the increment slightly slows down as the reaction proceeds. After 100 h, more than 35 mmol of H2O2 is produced with an average H2O2 production rate of 357 μmol h−1, eventually giving rise to more than 6 L of H2O2 solution with a concentration of 5.7 mM (Fig. 4b). The collected liquid product can be directly used for multiple applications. Using two bacteria Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli), as examples, we find that their growth is fully inhibited with the application of 5.7 mM H2O2 solution (Fig. 4c and Supplementary Fig. 26). Our product solution can also be employed in wastewater treatment as simulated by the Fenton reaction in the presence of methyl blue (MB) or methyl orange (MO) at practically relevant concentrations (100 ppm)60. Both organic dyes are observed to totally degrade within 30 s after the introduction of 5.7 mM H2O2 solution (Fig. 4d, e and Supplementary Fig. 27). The above results showcase that the dilute H2O2 solution produced from our biphasic fluid system can satisfactorily meet the demands of household disinfection and environmental remediation. The solution could be stored for over 1 month without significant degradation (Supplementary Fig. 28).Fig. 4 Continuous H2O2 production and extraction for practical applications.

a Total amount of H2O2 produced and its concentration change over time during an uninterrupted 100 h test in our biphasic fluid system. b Photographs of the as-obtained H2O2 solution. c Antibacterial tests against S. aureus and E. coli using the as-obtained H2O2 solution. d, e Degradation of d MB and e MO using the as-obtained H2O2 solution, insets are the photographs showing the dye decolorization.

To evaluate the economic feasibility of our biphasic fluid system, we carried out a techno-economic analysis (TEA) based on an amplified reactor device to determine the levelized cost of the product (LCP) and the end-of-life net present value (NPV)61,62. The estimation of the capital and operational costs is based on the prevailing market price of raw materials and products, as summarized in Supplementary Tables 2 and 3. It is found that when the FW/FO ratio is set at 1/4, LCP is most economical (Supplementary Fig. 29a). Assuming a facility lifespan of 10 years, the end-of-life NPV turns profitable by the fourth year (Supplementary Fig. 29b). These results demonstrate the practical viability of the biphasic fluid system in H2O2 production.

Discussion

In summary, we here demonstrated an innovative strategy for continuous H2O2 photosynthesis and extraction. The success key lies in the judicious design of both the photocatalyst material and the reactor. PF-BTTA-COF was prepared via the Schiff-base reaction between tritopic amine and tetratopic aldehyde monomers, followed by perfluoroalkyl functionalization at uncondensed aldehyde sites to afford its surface superhydrophobicity. Such a surface property allows the photocatalyst to be selectively and stably dispersed in oil instead of water. We then constructed a biphasic fluid system by co-feeding water and O2-saturated catalyst-dispersed TFT through transparent tubular flow channels to a coiled reactor under irradiation. The immiscibility of these two liquid phases led to the formation of a series of stable TFT-water biphasic segments with clear interfaces that promoted H2O2 spontaneous extraction. By properly adjusting reaction conditions, we achieved an unprecedented H2O2 production rate of up to 968 μmol h−1 and tunable H2O2 concentrations from 2.2 to 38.1 mM. As-obtained H2O2 solution could be directly supplied to end-users where and when it is needed, and can satisfactorily meet the practical requirements of disinfection and wastewater treatments. Moreover, our biphasic fluid system could be readily scaled up by increasing the channel length or connecting several coiled reactors in parallel or in series.

Methods

Synthesis of BTTA-COF and PF-BTTA-COF

Typically, BTDIPA (30.0 mg, 0.075 mmol) and 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TAPT) (26.6 mg, 0.075 mmol) were ultrasonically dispersed in a mixture of o-dichlorobenzene, n-butyl alcohol, and 6 M acetic acid (4.4 mL, 5/5/1, v/v/v) in a 25 mL Pyrex tube. The tube was degassed by three vacuum-N2 filling cycles, sealed under vacuum, and heated at 120 °C for 72 h. After cooled down to room temperature, the solid was collected by centrifugation, thoroughly washed with N,N-dimethylformamide (commercial sources and purities), anhydrous tetrahydrofuran, and acetone, respectively, and finally dried under vacuum at 80 °C overnight to afford BTTA-COF as a light-yellow powder (yield: 88%). For the synthesis of PF-BTTA-COF, BTTA-COF (100 mg) was ultrasonically dispersed in ethanol (5 mL), then added with UFHA (500 µL, 2.5 mmol) and acetic acid (50 µL) under stirring. The mixture was stirred at room temperature for 5 h under N2. The product was isolated by filtration, thoroughly washed with ethanol, and dried under vacuum at 80 °C overnight.

Determination of H2O2 concentration

The H2O2 concentration was determined using a colorimetric method as described in our previous publication34. Typically, a ferrous ion oxidation xylenol orange (FOX) solution was prepared by dissolving Fe(NH4)2(SO4)2·6H2O (19.61 mg), D-sorbitol (3.644 mg), and xylenol orange (XO) (14.333 mg) in deionized water (200 mL) added with ethanol (2 mL) and H2SO4 (98%, 272 μL). Subsequently, 50 μL of the obtained H2O2 solution (diluted if needed) was mixed with the pre-prepared FOX solution. The concentration of H2O2 was quantified by monitoring the characteristic absorption peak at 550 nm via UV-Vis spectroscopy according to the calibration curve (Supplementary Fig. 11).

Photocatalytic H2O2 production in a batch system

In a typical batch photocatalytic reaction, 10 mg of photocatalyst was dispersed in 10 mL of pure water (or with 10 vol% BA) inside a top-irradiated Pyrex reactor (120 mL). The suspension was first bubbled with O2 for 30 min before the reactor was carefully sealed. During the photocatalytic reaction, the reactor was irradiated by a 300 W Xe-lamp (China Education Au-light, CEL-HXF300) with a cutoff filter of 420 nm. The light intensity was calibrated to be 200 mW cm−2 using a Newport light-power meter (Model 1918-R). To monitor the reaction process, the reaction solution was extracted every 1 h and filtrated through a syringe filter (0.22 μm) to remove the photocatalyst powder. The resulting H2O2 concentration was quantified using the FOX solution.

Photocatalytic H2O2 production in the biphasic fluid system

In a typical photocatalytic reaction, 140 mg of PF-BTTA-COF photocatalyst was ultrasonically dispersed in 70 mL of TFT (with or without 10 vol% BA). The TFT dispersion (oil phase) and distilled water (water phase) were separately bubbled with O2 for 30 min, and then pumped through a T-shape valve at specific feeding rates by two peristaltic pumps and mixed together. This led to the formation of consecutive oil-water segments, which were fed into a coiled tubular reactor made of polypropylene tubing (Φ1.6 × 3.2 mm). The total tube length in the reactor is 44 m, corresponding to a total volume of ~90 mL. The solution retention time in the flow channel was controlled by the overall flow rate of water and oil. Inside the coiled reactor, the oil-water segments were side-irradiated by a set of LED arrays with a wavelength of 455 nm and a light intensity of 25 mW cm−2. During the photocatalytic reaction, generated H2O2 would migrate across abundant oil-water interfaces and accumulate in the water phase. After passing through the coiled reactor, the oil-water mixed solution was collected in a container, where phase separation occurred spontaneously due to the immiscibility of water and TFT. The upper H2O2 aqueous solution was directly extracted using a peristaltic pump for subsequent uses, while the lower photocatalyst dispersion was pumped back for the next reaction cycle. Such a system achieved continuous H2O2 production and extraction as well as photocatalyst recycling. The H2O2 concentration at the outlet was determined every 1 h using the FOX solution.

Long-term continuous H2O2 photosynthesis in the biphasic system

The long-term continuous photocatalysis in the biphasic fluid system was conducted under similar conditions. 1.2 g of PF-BTTA-COF was dispersed in 300 mL of O2-saturated TFT and BA (30 mL, 9:1, v/v). The flow rates of oil and water phases were kept at 1.04 mL min−1 and 2.08 mL min−1, respectively. The H2O2 concentration at the outlet was determined every 2 h using the FOX solution.

Antibacterial experiments

The antibacterial effect of the as-obtained H2O2 solution was estimated by the plate colony counting method. Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) were selected as the target bacteria. An individual colony was first cultured in a fresh LB agar plate by shaking at a speed of 200 rpm at 37 °C for 12 h. Then, 30 µL of the initial colony solution was subsequently diluted 100-fold and shaken for another 3 h at 37 °C to ensure bacterial growth in the log-phase, eventually resulting in ~106 colony-forming units (CFU) per milliliter. Then 100 µL of the bacterial solution was incubated with the as-obtained H2O2 solution (500 µL, 5.7 mM) for 3 h. The colonies were photographed after 24 h incubation at 37 °C. Control experiments were conducted under identical conditions except that H2O2 solution was not added.

Dye degradation experiments

Methyl blue (MB) and methyl orange (MO) were chosen as representative organic dyes for the degradation experiments using the Fenton reaction process. In a typical experiment, a stock solution containing dye (100 ppm) and FeSO4 (6 mM) was prepared, and its pH value was adjusted to 3.0 using diluted H2SO4. Subsequently, 2 mL of the as-obtained H2O2 solution (5.7 mM) was added to 2 mL of the above-mentioned dye solution in the dark. The absorbance of the organic dye at its maximum absorption wavelength was recorded using UV-Vis spectroscopy, and its concentration was calculated based on the calibration curve with standard solutions.

Supplementary information

Supplementary Information

Peer Review File

Source data

Source Data

Supplementary information

The online version contains supplementary material available at 10.1038/s41467-024-52405-3.

Acknowledgements

We acknowledge the financial support from National Natural Science Foundation of China (U2002213 and 52161160331), the Natural Science Foundation of Jiangsu Province (BK20220027), the Science and Technology Development Fund Macau SAR (0077/2021/A2), the Natural Science Foundation of the Jiangsu Higher Education Institutions of China (20KJA430002), and the Collaborative Innovation Center of Suzhou Nano Science and Technology. We thank Zihui Han and Prof. Liang Cheng for the antibacterial tests. We thank Yuhang Wang for techno-economic analysis.

Author contributions

W.H. and Y.G.L. conceived the project and designed the experiments. C.S. synthesized the catalysts and performed the structural characterizations and photocatalytic tests. C.S. and X.Y. carried out the long-time performance evaluation. Y.J. and Y.Y.L. conducted the structural simulations. J.X. and Y.Y. performed the HR-TEM imaging and EDS mapping. Y.H. assisted on the quantification of H2O2. C.S., W.H., and Y.G.L. co-wrote the manuscript with contributions from all co-authors.

Peer review

Peer review information

Nature Communications thanks Pradip Pachfule, Hai-Long Jiang and Zhuofeng Hu, who co-reviewed with Jimmy Yu, for their contribution to the peer review of this work. A peer review file is available.

Data availability

All the data that support the findings of this study are provided in the Supplementary Information. Other data are available from the corresponding author upon request. Source data are provided with this paper.

Competing interests

The authors declare no competing interests.

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
==== Refs
References

1. Ciriminna R Albanese L Meneguzzo F Pagliaro M Hydrogen peroxide: a key chemical for today’s sustainable development ChemSusChem 2016 9 3374 3381 10.1002/cssc.201600895 27813285
Ciriminna, R., Albanese, L., Meneguzzo, F. & Pagliaro, M. Hydrogen peroxide: a key chemical for today’s sustainable development. ChemSusChem 9, 3374–3381 (2016).27813285 10.1002/cssc.201600895
2. McDonnell, G. The use of hydrogen peroxide for disinfection and sterilization applications in Patai’s Chemistry of Functional Groups, 1–34 (Wiley, 2014).
3. Kumar, G. Hydrogen Peroxide Price Trend, Monitor, Supply & Demand, Forecast. https://www.linkedin.com/pulse/hydrogen-peroxide-price-trend-monitor-supply-demand-kumar-gupta-fyu9c (2024).
4. Campos‐Martin JM Blanco‐Brieva G Fierro JLG Hydrogen peroxide synthesis: an outlook beyond the anthraquinone process Angew. Chem. Int. Ed. Engl. 2006 45 6962 6984 10.1002/anie.200503779 17039551
Campos‐Martin, J. M., Blanco‐Brieva, G. & Fierro, J. L. G. Hydrogen peroxide synthesis: an outlook beyond the anthraquinone process. Angew. Chem. Int. Ed. Engl. 45, 6962–6984 (2006).17039551 10.1002/anie.200503779
5. Pi L Generation of H2O2 by on-site activation of molecular dioxygen for environmental remediation applications: a review Chem. Eng. J. 2020 389 123420 10.1016/j.cej.2019.123420
Pi, L. et al. Generation of H2O2 by on-site activation of molecular dioxygen for environmental remediation applications: a review. Chem. Eng. J. 389, 123420 (2020).10.1016/j.cej.2019.123420
6. Xia C Xia Y Zhu P Fan L Wang H Direct electrosynthesis of pure aqueous H2O2 solutions up to 20% by weight using a solid electrolyte Science 2019 366 226 231 10.1126/science.aay1844 31601767
Xia, C., Xia, Y., Zhu, P., Fan, L. & Wang, H. Direct electrosynthesis of pure aqueous H2O2 solutions up to 20% by weight using a solid electrolyte. Science 366, 226–231 (2019).31601767 10.1126/science.aay1844
7. Yang S Toward the decentralized electrochemical production of H2O2: a focus on the catalysis ACS Catal. 2018 8 4064 4081 10.1021/acscatal.8b00217
Yang, S. et al. Toward the decentralized electrochemical production of H2O2: a focus on the catalysis. ACS Catal. 8, 4064–4081 (2018).10.1021/acscatal.8b00217
8. Sun Y Han L Strasser P A comparative perspective of electrochemical and photochemical approaches for catalytic H2O2 production Chem. Soc. Rev. 2020 49 6605 6631 10.1039/D0CS00458H 32760937
Sun, Y., Han, L. & Strasser, P. A comparative perspective of electrochemical and photochemical approaches for catalytic H2O2 production. Chem. Soc. Rev. 49, 6605–6631 (2020).32760937 10.1039/D0CS00458H
9. Hou H Zeng X Zhang X Production of hydrogen peroxide by photocatalytic processes Angew. Chem. Int. Ed. Engl. 2020 59 17356 17376 10.1002/anie.201911609 31571331
Hou, H., Zeng, X. & Zhang, X. Production of hydrogen peroxide by photocatalytic processes. Angew. Chem. Int. Ed. Engl. 59, 17356–17376 (2020).31571331 10.1002/anie.201911609
10. Qu S Wu H Ng YH Clean production of hydrogen peroxide: a heterogeneous solar‐driven redox process Adv. Energy Mater. 2023 13 2301047 10.1002/aenm.202301047
Qu, S., Wu, H. & Ng, Y. H. Clean production of hydrogen peroxide: a heterogeneous solar‐driven redox process. Adv. Energy Mater. 13, 2301047 (2023).10.1002/aenm.202301047
11. Freese T Meijer JT Feringa BL Beil SB An organic perspective on photocatalytic production of hydrogen peroxide Nat. Catal. 2023 6 553 558 10.1038/s41929-023-00980-x
Freese, T., Meijer, J. T., Feringa, B. L. & Beil, S. B. An organic perspective on photocatalytic production of hydrogen peroxide. Nat. Catal. 6, 553–558 (2023).10.1038/s41929-023-00980-x
12. Wang L Inorganic metal‐oxide photocatalyst for H2O2 production Small 2021 18 2104561 10.1002/smll.202104561
Wang, L. et al. Inorganic metal‐oxide photocatalyst for H2O2 production. Small 18, 2104561 (2021).10.1002/smll.202104561
13. Kondo Y Kuwahara Y Mori K Yamashita H Design of metal-organic framework catalysts for photocatalytic hydrogen peroxide production Chem 2022 8 2924 2938 10.1016/j.chempr.2022.10.007
Kondo, Y., Kuwahara, Y., Mori, K. & Yamashita, H. Design of metal-organic framework catalysts for photocatalytic hydrogen peroxide production. Chem 8, 2924–2938 (2022).10.1016/j.chempr.2022.10.007
14. Yu X Hu Y Shao C Huang W Li Y Polymer semiconductors: a unique platform for photocatalytic hydrogen peroxide production Mater. Today 2023 71 152 173 10.1016/j.mattod.2023.10.005
Yu, X., Hu, Y., Shao, C., Huang, W. & Li, Y. Polymer semiconductors: a unique platform for photocatalytic hydrogen peroxide production. Mater. Today 71, 152–173 (2023).10.1016/j.mattod.2023.10.005
15. Yong Z Ma T Solar‐to‐H2O2 catalyzed by covalent organic frameworks Angew. Chem. Int. Ed. Engl. 2023 62 e202308980 10.1002/anie.202308980 37574706
Yong, Z. & Ma, T. Solar‐to‐H2O2 catalyzed by covalent organic frameworks. Angew. Chem. Int. Ed. Engl. 62, e202308980 (2023).37574706 10.1002/anie.202308980
16. Zeng X Liu Y Hu X Zhang X Photoredox catalysis over semiconductors for light-driven hydrogen peroxide production Green. Chem. 2021 23 1466 1494 10.1039/D0GC04236F
Zeng, X., Liu, Y., Hu, X. & Zhang, X. Photoredox catalysis over semiconductors for light-driven hydrogen peroxide production. Green. Chem. 23, 1466–1494 (2021).10.1039/D0GC04236F
17. Ding Y Emerging semiconductors and metal-organic-compounds-related photocatalysts for sustainable hydrogen peroxide production Matter 2022 5 2119 2167 10.1016/j.matt.2022.05.011
Ding, Y. et al. Emerging semiconductors and metal-organic-compounds-related photocatalysts for sustainable hydrogen peroxide production. Matter 5, 2119–2167 (2022).10.1016/j.matt.2022.05.011
18. Isaka Y Kawase Y Kuwahara Y Mori K Yamashita H Two‐phase system utilizing hydrophobic metal-organic frameworks (MOFs) for photocatalytic synthesis of hydrogen peroxide Angew. Chem. Int. Ed. Engl. 2019 58 5402 5406 10.1002/anie.201901961 30793452
Isaka, Y., Kawase, Y., Kuwahara, Y., Mori, K. & Yamashita, H. Two‐phase system utilizing hydrophobic metal-organic frameworks (MOFs) for photocatalytic synthesis of hydrogen peroxide. Angew. Chem. Int. Ed. Engl. 58, 5402–5406 (2019).30793452 10.1002/anie.201901961
19. Zhao W Accelerated synthesis and discovery of covalent organic framework photocatalysts for hydrogen peroxide production J. Am. Chem. Soc. 2022 144 9902 9909 10.1021/jacs.2c02666 35635501
Zhao, W. et al. Accelerated synthesis and discovery of covalent organic framework photocatalysts for hydrogen peroxide production. J. Am. Chem. Soc. 144, 9902–9909 (2022).35635501 10.1021/jacs.2c02666
20. Li L Xu L Hu Z Yu JC Enhanced mass transfer of oxygen through a gas-liquid-solid interface for photocatalytic hydrogen peroxide production Adv. Funct. Mater. 2021 31 2106120 10.1002/adfm.202106120
Li, L., Xu, L., Hu, Z. & Yu, J. C. Enhanced mass transfer of oxygen through a gas-liquid-solid interface for photocatalytic hydrogen peroxide production. Adv. Funct. Mater. 31, 2106120 (2021).10.1002/adfm.202106120
21. Yan S Photocatalytic H2O2 generation reaction with a benchmark rate at air-liquid-solid joint interfaces Adv. Mater. 2023 36 2307967 10.1002/adma.202307967
Yan, S. et al. Photocatalytic H2O2 generation reaction with a benchmark rate at air-liquid-solid joint interfaces. Adv. Mater. 36, 2307967 (2023).10.1002/adma.202307967
22. Cambié D Bottecchia C Straathof NJW Hessel V Noël T Applications of continuous-flow photochemistry in organic synthesis, material science, and water treatment Chem. Rev. 2016 116 10276 10341 10.1021/acs.chemrev.5b00707 26935706
Cambié, D., Bottecchia, C., Straathof, N. J. W., Hessel, V. & Noël, T. Applications of continuous-flow photochemistry in organic synthesis, material science, and water treatment. Chem. Rev. 116, 10276–10341 (2016).26935706 10.1021/acs.chemrev.5b00707
23. Pieber B Shalom M Antonietti M Seeberger PH Gilmore K Continuous heterogeneous photocatalysis in serial micro‐batch reactors Angew. Chem. Int. Ed. Engl. 2018 57 9976 9979 10.1002/anie.201712568 29377383
Pieber, B., Shalom, M., Antonietti, M., Seeberger, P. H. & Gilmore, K. Continuous heterogeneous photocatalysis in serial micro‐batch reactors. Angew. Chem. Int. Ed. Engl. 57, 9976–9979 (2018).29377383 10.1002/anie.201712568
24. Byun J Hong Y Zhang KAI Beyond the batch: process and material design of polymeric photocatalysts for flow photochemistry Chem. Catal. 2021 1 771 781 10.1016/j.checat.2021.08.003
Byun, J., Hong, Y. & Zhang, K. A. I. Beyond the batch: process and material design of polymeric photocatalysts for flow photochemistry. Chem. Catal. 1, 771–781 (2021).10.1016/j.checat.2021.08.003
25. Wen Y Electrochemical reactors for continuous decentralized H2O2 production Angew. Chem. Int. Ed. Engl. 2022 61 e202205972 10.1002/anie.202205972 35698896
Wen, Y. et al. Electrochemical reactors for continuous decentralized H2O2 production. Angew. Chem. Int. Ed. Engl. 61, e202205972 (2022).35698896 10.1002/anie.202205972
26. Liu R Linkage-engineered donor-acceptor covalent organic frameworks for optimal photosynthesis of hydrogen peroxide from water and air Nat. Catal. 2024 7 195 206 10.1038/s41929-023-01102-3
Liu, R. et al. Linkage-engineered donor-acceptor covalent organic frameworks for optimal photosynthesis of hydrogen peroxide from water and air. Nat. Catal. 7, 195–206 (2024).10.1038/s41929-023-01102-3
27. Huang W Luo W Li Y Two-dimensional semiconducting covalent organic frameworks for photocatalytic solar fuel production Mater. Today 2020 40 160 172 10.1016/j.mattod.2020.07.003
Huang, W., Luo, W. & Li, Y. Two-dimensional semiconducting covalent organic frameworks for photocatalytic solar fuel production. Mater. Today 40, 160–172 (2020).10.1016/j.mattod.2020.07.003
28. Liu R Covalent organic frameworks: an ideal platform for designing ordered materials and advanced applications Chem. Soc. Rev. 2021 50 120 242 10.1039/D0CS00620C 33283811
Liu, R. et al. Covalent organic frameworks: an ideal platform for designing ordered materials and advanced applications. Chem. Soc. Rev. 50, 120–242 (2021).33283811 10.1039/D0CS00620C
29. Gong Y-N Guan X Jiang H-L Covalent organic frameworks for photocatalysis: synthesis, structural features, fundamentals and performance Coord. Chem. Rev. 2023 475 214889 10.1016/j.ccr.2022.214889
Gong, Y.-N., Guan, X. & Jiang, H.-L. Covalent organic frameworks for photocatalysis: synthesis, structural features, fundamentals and performance. Coord. Chem. Rev. 475, 214889 (2023).10.1016/j.ccr.2022.214889
30. Qian Y Computation-based regulation of excitonic effects in donor-acceptor covalent organic frameworks for enhanced photocatalysis Nat. Commun. 2023 14 3083 10.1038/s41467-023-38884-w 37248231
Qian, Y. et al. Computation-based regulation of excitonic effects in donor-acceptor covalent organic frameworks for enhanced photocatalysis. Nat. Commun. 14, 3083 (2023).37248231 10.1038/s41467-023-38884-w
31. Qian Y Jiang H-L Structural regulation of covalent organic frameworks for catalysis Acc. Chem. Res. 2024 57 1214 1226 10.1021/acs.accounts.4c00061 38552221
Qian, Y. & Jiang, H.-L. Structural regulation of covalent organic frameworks for catalysis. Acc. Chem. Res. 57, 1214–1226 (2024).38552221 10.1021/acs.accounts.4c00061
32. Huang W Highly crystalline and water-wettable benzobisthiazole-based covalent organic frameworks for enhanced photocatalytic hydrogen production Natl Sci. Rev. 2023 10 nwac171 10.1093/nsr/nwac171 36684521
Huang, W. et al. Highly crystalline and water-wettable benzobisthiazole-based covalent organic frameworks for enhanced photocatalytic hydrogen production. Natl Sci. Rev. 10, nwac171 (2023).36684521 10.1093/nsr/nwac171
33. Chen L Acetylene and diacetylene functionalized covalent triazine frameworks as metal‐free photocatalysts for hydrogen peroxide production: a new two‐electron water oxidation pathway Adv. Mater. 2019 32 1904433 10.1002/adma.201904433
Chen, L. et al. Acetylene and diacetylene functionalized covalent triazine frameworks as metal‐free photocatalysts for hydrogen peroxide production: a new two‐electron water oxidation pathway. Adv. Mater. 32, 1904433 (2019).10.1002/adma.201904433
34. Shao C A covalent organic framework inspired by C3N4 for photosynthesis of hydrogen peroxide with high quantum efficiency Chin. J. Catal. 2023 46 28 35 10.1016/S1872-2067(22)64205-0
Shao, C. et al. A covalent organic framework inspired by C3N4 for photosynthesis of hydrogen peroxide with high quantum efficiency. Chin. J. Catal. 46, 28–35 (2023).10.1016/S1872-2067(22)64205-0
35. Chang JN Oxidation‐reduction molecular junction covalent organic frameworks for full reaction photosynthesis of H2O2 Angew. Chem. Int. Ed. Engl. 2023 62 e202218868 10.1002/anie.202218868 36581593
Chang, J. N. et al. Oxidation‐reduction molecular junction covalent organic frameworks for full reaction photosynthesis of H2O2. Angew. Chem. Int. Ed. Engl. 62, e202218868 (2023).36581593 10.1002/anie.202218868
36. Ding S-Y Construction of covalent organic framework for catalysis: Pd/COF-LZU1 in Suzuki–Miyaura coupling reaction J. Am. Chem. Soc. 2011 133 19816 19822 10.1021/ja206846p 22026454
Ding, S.-Y. et al. Construction of covalent organic framework for catalysis: Pd/COF-LZU1 in Suzuki–Miyaura coupling reaction. J. Am. Chem. Soc. 133, 19816–19822 (2011).22026454 10.1021/ja206846p
37. Liao Q Donor-acceptor type [4+3] covalent organic frameworks: sub-stoichiometric synthesis and photocatalytic application Sci. China Chem. 2020 63 707 714 10.1007/s11426-019-9696-3
Liao, Q. et al. Donor-acceptor type [4+3] covalent organic frameworks: sub-stoichiometric synthesis and photocatalytic application. Sci. China Chem. 63, 707–714 (2020).10.1007/s11426-019-9696-3
38. Lu M Confining and highly dispersing single polyoxometalate clusters in covalent organic frameworks by covalent linkages for CO2 photoreduction J. Am. Chem. Soc. 2022 144 1861 1871 10.1021/jacs.1c11987 35050618
Lu, M. et al. Confining and highly dispersing single polyoxometalate clusters in covalent organic frameworks by covalent linkages for CO2 photoreduction. J. Am. Chem. Soc. 144, 1861–1871 (2022).35050618 10.1021/jacs.1c11987
39. Sun Q Integrating superwettability within covalent organic frameworks for functional coating Chem 2018 4 1726 1739 10.1016/j.chempr.2018.05.020
Sun, Q. et al. Integrating superwettability within covalent organic frameworks for functional coating. Chem 4, 1726–1739 (2018).10.1016/j.chempr.2018.05.020
40. Enders AA North NM Fensore CM Velez-Alvarez J Allen HC Functional group identification for FTIR spectra using image-based machine learning models Anal. Chem. 2021 93 9711 9718 10.1021/acs.analchem.1c00867 34190551
Enders, A. A., North, N. M., Fensore, C. M., Velez-Alvarez, J. & Allen, H. C. Functional group identification for FTIR spectra using image-based machine learning models. Anal. Chem. 93, 9711–9718 (2021).34190551 10.1021/acs.analchem.1c00867
41. Dai F Zhuang Q Huang G Deng H Zhang X Infrared spectrum characteristics and quantification of OH groups in coal ACS Omega 2023 8 17064 17076 10.1021/acsomega.3c01336 37214670
Dai, F., Zhuang, Q., Huang, G., Deng, H. & Zhang, X. Infrared spectrum characteristics and quantification of OH groups in coal. ACS Omega 8, 17064–17076 (2023).37214670 10.1021/acsomega.3c01336
42. Liao Q Regulating relative nitrogen locations of diazine functionalized covalent organic frameworks for overall H2O2 photosynthesis Angew. Chem. Int. Ed. Engl. 2023 62 e202310556 10.1002/anie.202310556 37632257
Liao, Q. et al. Regulating relative nitrogen locations of diazine functionalized covalent organic frameworks for overall H2O2 photosynthesis. Angew. Chem. Int. Ed. Engl. 62, e202310556 (2023).37632257 10.1002/anie.202310556
43. Yu H Vinyl-group-anchored covalent organic framework for promoting the photocatalytic generation of hydrogen peroxide Angew. Chem. Int. Ed. Engl. 2024 63 e202402297 10.1002/anie.202402297 38488772
Yu, H. et al. Vinyl-group-anchored covalent organic framework for promoting the photocatalytic generation of hydrogen peroxide. Angew. Chem. Int. Ed. Engl. 63, e202402297 (2024).38488772 10.1002/anie.202402297
44. Zhi Q Piperazine-linked metalphthalocyanine frameworks for highly efficient visible-light-driven H2O2 photosynthesis J. Am. Chem. Soc. 2022 144 21328 21336 10.1021/jacs.2c09482 36350764
Zhi, Q. et al. Piperazine-linked metalphthalocyanine frameworks for highly efficient visible-light-driven H2O2 photosynthesis. J. Am. Chem. Soc. 144, 21328–21336 (2022).36350764 10.1021/jacs.2c09482
45. Kou M Molecularly engineered covalent organic frameworks for hydrogen peroxide photosynthesis Angew. Chem. Int. Ed. Engl. 2022 61 e202200413 10.1002/anie.202200413 35166425
Kou, M. et al. Molecularly engineered covalent organic frameworks for hydrogen peroxide photosynthesis. Angew. Chem. Int. Ed. Engl. 61, e202200413 (2022).35166425 10.1002/anie.202200413
46. Liu Y Fluorination of covalent organic framework reinforcing the confinement of Pd nanoclusters enhances hydrogen peroxide photosynthesis J. Am. Chem. Soc. 2023 145 19877 19884 10.1021/jacs.3c05914 37584527
Liu, Y. et al. Fluorination of covalent organic framework reinforcing the confinement of Pd nanoclusters enhances hydrogen peroxide photosynthesis. J. Am. Chem. Soc. 145, 19877–19884 (2023).37584527 10.1021/jacs.3c05914
47. Cheng H Rational design of covalent heptazine frameworks with spatially separated redox centers for high‐efficiency photocatalytic hydrogen peroxide production Adv. Mater. 2021 34 2107480 10.1002/adma.202107480
Cheng, H. et al. Rational design of covalent heptazine frameworks with spatially separated redox centers for high‐efficiency photocatalytic hydrogen peroxide production. Adv. Mater. 34, 2107480 (2021).10.1002/adma.202107480
48. Zhang Y H2O2 generation from O2 and H2O on a near-infrared absorbing porphyrin supramolecular photocatalyst Nat. Energy 2023 8 361 371 10.1038/s41560-023-01218-7
Zhang, Y. et al. H2O2 generation from O2 and H2O on a near-infrared absorbing porphyrin supramolecular photocatalyst. Nat. Energy 8, 361–371 (2023).10.1038/s41560-023-01218-7
49. Das P Roeser J Thomas A Solar light driven H2O2 production and selective oxidations using a covalent organic framework photocatalyst prepared by a multicomponent reaction Angew. Chem. Int. Ed. Engl. 2023 62 e202304349 10.1002/anie.202304349 37150745
Das, P., Roeser, J. & Thomas, A. Solar light driven H2O2 production and selective oxidations using a covalent organic framework photocatalyst prepared by a multicomponent reaction. Angew. Chem. Int. Ed. Engl. 62, e202304349 (2023).37150745 10.1002/anie.202304349
50. Buzzetti L Crisenza GEM Melchiorre P Mechanistic studies in photocatalysis Angew. Chem. Int. Ed. Engl. 2019 58 3730 3747 10.1002/anie.201809984 30339746
Buzzetti, L., Crisenza, G. E. M. & Melchiorre, P. Mechanistic studies in photocatalysis. Angew. Chem. Int. Ed. Engl. 58, 3730–3747 (2019).30339746 10.1002/anie.201809984
51. Dias AMA Gonçalves CMB Legido JL Coutinho JAP Marrucho IM Solubility of oxygen in substituted perfluorocarbons Fluid Phase Equilib. 2005 238 7 12 10.1016/j.fluid.2005.09.011
Dias, A. M. A., Gonçalves, C. M. B., Legido, J. L., Coutinho, J. A. P. & Marrucho, I. M. Solubility of oxygen in substituted perfluorocarbons. Fluid Phase Equilib. 238, 7–12 (2005).10.1016/j.fluid.2005.09.011
52. Adamiak W Hydrogen and hydrogen peroxide formation in trifluorotoluene-water biphasic systems J. Phys. Chem. C 2014 118 23154 23161 10.1021/jp507310d
Adamiak, W. et al. Hydrogen and hydrogen peroxide formation in trifluorotoluene-water biphasic systems. J. Phys. Chem. C 118, 23154–23161 (2014).10.1021/jp507310d
53. Pang Y Xie H Sun Y Titirici M-M Chai G-L Electrochemical oxygen reduction for H2O2 production: catalysts, pH effects and mechanisms J. Mater. Chem. A 2020 8 24996 25016 10.1039/D0TA09122G
Pang, Y., Xie, H., Sun, Y., Titirici, M.-M. & Chai, G.-L. Electrochemical oxygen reduction for H2O2 production: catalysts, pH effects and mechanisms. J. Mater. Chem. A 8, 24996–25016 (2020).10.1039/D0TA09122G
54. Luo Y Sulfone‐modified covalent organic frameworks enabling efficient photocatalytic hydrogen peroxide generation via one‐step two‐electron O2 reduction Angew. Chem. Int. Ed. Engl. 2023 62 e202305355 10.1002/anie.202305355 37096446
Luo, Y. et al. Sulfone‐modified covalent organic frameworks enabling efficient photocatalytic hydrogen peroxide generation via one‐step two‐electron O2 reduction. Angew. Chem. Int. Ed. Engl. 62, e202305355 (2023).37096446 10.1002/anie.202305355
55. Liu Y Substoichiometric covalent organic frameworks with uncondensed aldehyde for highly efficient hydrogen peroxide photosynthesis in pure water Appl. Catal. B 2023 331 122691 10.1016/j.apcatb.2023.122691
Liu, Y. et al. Substoichiometric covalent organic frameworks with uncondensed aldehyde for highly efficient hydrogen peroxide photosynthesis in pure water. Appl. Catal. B 331, 122691 (2023).10.1016/j.apcatb.2023.122691
56. Qin C Dual donor-acceptor covalent organic frameworks for hydrogen peroxide photosynthesis Nat. Commun. 2023 14 5238 10.1038/s41467-023-40991-7 37640726
Qin, C. et al. Dual donor-acceptor covalent organic frameworks for hydrogen peroxide photosynthesis. Nat. Commun. 14, 5238 (2023).37640726 10.1038/s41467-023-40991-7
57. Hao F Photo‐driven quasi‐topological transformation exposing highly active nitrogen cation sites for enhanced photocatalytic H2O2 production Angew. Chem. Int. Ed. Engl. 2023 62 e202315456 10.1002/anie.202315456 37933417
Hao, F. et al. Photo‐driven quasi‐topological transformation exposing highly active nitrogen cation sites for enhanced photocatalytic H2O2 production. Angew. Chem. Int. Ed. Engl. 62, e202315456 (2023).37933417 10.1002/anie.202315456
58. Mou Y Linkage microenvironment of azoles‐related covalent organic frameworks precisely regulates photocatalytic generation of hydrogen peroxide Angew. Chem. Int. Ed. Engl. 2023 62 e202309480 10.1002/anie.202309480 37462327
Mou, Y. et al. Linkage microenvironment of azoles‐related covalent organic frameworks precisely regulates photocatalytic generation of hydrogen peroxide. Angew. Chem. Int. Ed. Engl. 62, e202309480 (2023).37462327 10.1002/anie.202309480
59. Chen D Covalent organic frameworks containing dual O2 reduction centers for overall photosynthetic hydrogen peroxide production Angew. Chem. Int. Ed. Engl. 2023 62 e202217479 10.1002/anie.202217479 36576381
Chen, D. et al. Covalent organic frameworks containing dual O2 reduction centers for overall photosynthetic hydrogen peroxide production. Angew. Chem. Int. Ed. Engl. 62, e202217479 (2023).36576381 10.1002/anie.202217479
60. Yaseen DA Scholz M Textile dye wastewater characteristics and constituents of synthetic effluents: a critical review Int. J. Environ. Sci. Technol. 2019 16 1193 1226 10.1007/s13762-018-2130-z
Yaseen, D. A. & Scholz, M. Textile dye wastewater characteristics and constituents of synthetic effluents: a critical review. Int. J. Environ. Sci. Technol. 16, 1193–1226 (2019).10.1007/s13762-018-2130-z
61. Zhao H Rational design of carbon nitride for remarkable photocatalytic H2O2 production Chem. Catal. 2022 2 1720 1733 10.1016/j.checat.2022.04.015
Zhao, H. et al. Rational design of carbon nitride for remarkable photocatalytic H2O2 production. Chem. Catal. 2, 1720–1733 (2022).10.1016/j.checat.2022.04.015
62. Chi M Spatial decoupling of bromide-mediated process boosts propylene oxide electrosynthesis Nat. Commun. 2024 15 3646 10.1038/s41467-024-48070-1 38684683
Chi, M. et al. Spatial decoupling of bromide-mediated process boosts propylene oxide electrosynthesis. Nat. Commun. 15, 3646 (2024).38684683 10.1038/s41467-024-48070-1
