Key Takeaways & Executive Findings
- •• • Uranyl decoration on imine-based COFs boosts H2O2 production by 1.6–10.1 folds across pH 2–11, with optimal rate of 1435.9 μmol g−1 h−1 (28.72 mmol g(U)−1 h−1) under visible light, demonstrating universal pH applicability for industrial wastewater treatment. • • The enhanced performance stems from accelerated oxygen activation and favored formation of ·O2− and *OOH intermediates, facilitating the two-step single-electron ORR, which is critical for selective H2O2 synthesis. • • The optimal catalyst, uranyl-decorated TTa-COF, achieves a high space-time yield of 28.72 mmol per gram of uranium per hour, indicating efficient use of uranium as a cocatalyst, which is economically relevant for precious metal replacement. • • The work provides a new strategy for designing uranyl-based photocatalysts, expanding the application of uranium chemistry beyond nuclear energy, with potential for scalable solar-driven H2O2 production.
Abstract
Photocatalytic synthesis has been considered a promising technology for solar-to-chemicals conversion. Here, a series of novel photocatalysts was synthesized by decorating uranyl sites on imine-based covalent organic frameworks (i-COF) and proved functioning for the uniformly boosted H2O2 production by 1.6–10.1 folds compared with the bare i-COFs in a wide pH range from 2 to 11. Typically, an optimal H2O2 production rate of 1435.9 μmol g−1 h−1, i.e., 28.72 mmol g(U)−1 h−1, was realized over uranyl decorated TTa-COFs under visible light. Systematic investigations reveal that the universally and remarkably promoted performance is attributed to the outstanding electron-transfer ability, accelerated activation of molecular oxygen and favored formation of ·O2− and *OOH as the key intermediate by virtue of the decorated uranyl ions; thus the two-step single-electron oxygen reduction reaction (ORR) for H2O2 photo-generation is significantly facilitated. This work paves a new way for the uranyl-decorated COFs as a novel photocatalyst and provides in-depth insight to the reaction mechanism for photocatalytic H2O2 production.
1. Introduction
Hydrogen peroxide (H2O2) is a versatile oxidant essential in medicine, chemical synthesis, and environmental remediation, with global demand projected to reach 5.7 million tons per year by 2028. The dominant industrial anthraquinone process is energy-intensive and environmentally hazardous. Photocatalytic H2O2 production via oxygen reduction offers a green alternative, but its efficiency is limited by poor charge separation and sluggish oxygen activation kinetics. Conventional photocatalysts often suffer from rapid electron-hole recombination and insufficient active sites for O2 adsorption and reduction, leading to low H2O2 yields and poor selectivity.
This study addresses these bottlenecks by decorating imine-based covalent organic frameworks (i-COFs) with uranyl ions ([UO2]2+). Uranyl species, with their unique electronic structure and redox versatility, act as efficient cocatalysts that enhance electron transfer and promote the two-step single-electron oxygen reduction reaction (ORR). The resulting uranyl-decorated COFs exhibit significantly boosted H2O2 production rates across a wide pH range, outperforming bare COFs by up to an order of magnitude. This work introduces a novel application of uranium chemistry in photocatalysis, offering a promising route to efficient and sustainable H2O2 synthesis.
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Zewen Shen, Yana Chen, Ruiqing Cai, Yang Liu, Yezi Hu, Na Wang, Haotian Zhang, Guixia Zhao, Yanyu Liu, Xiubing Huang, Xiangke Wang (2026). Accelerated oxygen activation over uranyl decorated covalent organic framework for universally promoted H2O2 photosynthesis. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3700-7
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Frequently Asked Questions
What is the stability of the uranyl-decorated COF under prolonged irradiation and in varying pH conditions?
The study reports boosted H2O2 production across pH 2–11, indicating stability in acidic to alkaline media. However, long-term operational stability data (e.g., cycling tests) are not provided in the abstract. Further investigation is needed to assess photostability and potential uranyl leaching.
How does the H2O2 production rate compare with state-of-the-art photocatalysts on a per-active-site basis?
The optimal rate is 1435.9 μmol g−1 h−1, which corresponds to 28.72 mmol g(U)−1 h−1. This per-uranium rate is exceptionally high, suggesting that uranyl sites are highly efficient. However, direct comparison with other catalysts requires normalization by active site density and reaction conditions.
What is the selectivity for H2O2 versus competing products like water?
The abstract emphasizes the two-step single-electron ORR pathway via ·O2− and *OOH intermediates, which is selective for H2O2. However, quantitative selectivity data (e.g., electron number, H2O2 yield vs. H2O) are not provided. Detailed product analysis is necessary to confirm high selectivity.
What is the role of the imine linkage in the COF structure for uranyl coordination and photocatalytic activity?
The imine-based COF provides nitrogen-rich coordination sites for uranyl binding, which likely enhances electron transfer and oxygen activation. The study indicates that uranyl decoration on i-COFs leads to universally promoted performance, but the exact coordination environment and its effect on band structure are not detailed in the abstract.
What are the scalability prospects for this photocatalyst system?
The synthesis of uranyl-decorated COFs involves solution-based methods that are potentially scalable. However, the use of uranium raises concerns about radioactivity and regulatory compliance. The high per-uranium activity suggests that only trace amounts of uranium are needed, mitigating some concerns. Further engineering and life-cycle assessment are required.
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