Chemists at the National University of Singapore (NUS) have made a breakthrough in the field of chemical synthesis by developing hexavalent photocatalytic covalent organic frameworks (COFs). These frameworks have the potential to mimic natural photosynthesis to produce hydrogen peroxide (H2O2), a vital industrial chemical.

The Need for Innovation

Traditionally, the production of H2O2 has been done using anthraquinone as a catalyst, involving costly noble metal catalysts, high-pressure hydrogen gas, and hazardous solvents. This process is energy-intensive and not environmentally friendly. The research conducted by the NUS team aims to offer a sustainable and efficient alternative to this conventional method.

The artificial photosynthesis process faces several challenges, including insufficient charge carrier generation, limited catalytic sites, and inefficient delivery of charges and reactants to catalytic sites. Overcoming these obstacles is crucial for enhancing the efficiency and productivity of the photocatalytic system.

Led by Professor Donglin Jiang, the NUS research team devised a new strategy to develop hexavalent photocatalytic COFs. These COFs are porous, crystalline materials constructed from organic molecules linked by strong covalent bonds. Their flexibility allows for the systematic design of the π skeletons and pores, making them ideal for constructing efficient photocatalysts.

The researchers created donor-alt-acceptor framework photocatalysts that convert into catalytic scaffolds with dense catalytic sites upon irradiation. The spatially segregated donor and acceptor columns facilitate holes and electrons’ separation, preventing charge recombination and enabling rapid charge transport. Additionally, the engineered hydrophilic pore walls facilitate the passage of water and dissolved oxygen to reach the catalytic sites via capillary effect.

The COFs function as efficient photocatalysts for H2O2 production using only water, air, and light. They demonstrate a production rate of 7.2 mmol g–1 h–1, an optimal apparent quantum yield of 18.0%, and a solar-to-chemical conversion efficiency of 0.91% in bath reactors. When integrated into flow reactors, they sustainably produce over 15 liters of pure H2O2 solution under ambient conditions, showcasing operational stability over a two-week period.

Professor Jiang emphasized that the development of these novel photocatalysts represents nearly two decades of collective efforts in the COF field. The efficient delivery of charges and reactants to catalytic sites is crucial for addressing the challenges in artificial photosynthesis and achieving significant advancements in H2O2 production. The innovative approach taken by the NUS research team holds immense promise for the future of sustainable chemical synthesis.

Chemistry

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