Covalent Organic Cage-Based Photocatalysts for Highly Efficient and Selective H₂O₂ Production

Area of Science:

• Materials Science
• Photocatalysis
• Green Chemistry

Background:

• Sustainable hydrogen peroxide (H2O2) production is crucial.
• Existing polymeric or composite photocatalysts have limitations in solubility, architecture, and mechanistic understanding.
• Discrete, metal-free photocatalysts are needed for well-defined structure-function relationships.

Purpose of the Study:

• To develop novel, discrete, metal-free photocatalysts for H2O2 generation.
• To investigate the structure-activity relationships of covalent organic superphane cages.
• To explore their potential in solar-to-chemical energy conversion and environmental applications.

Main Methods:

• Synthesis of covalent organic superphane cages with amine functionalities.
• Photocatalytic evaluation for H2O2 production under visible light.
• Characterization using spectroscopy and density functional theory (DFT) calculations.
• Assessment of reaction pathways (WOR, ORR) and charge transport dynamics.

Main Results:

• The tied tertiary amine derivative (SUPE-ptz-2) demonstrated superior performance.
• Achieved H2O2 production rate of 11,089 µmol h⁻¹ g⁻¹ (25,031 µmol h⁻¹ g⁻¹ with isopropanol).
• Apparent quantum yield of 29.2% at 400 nm and 93% selectivity for the two-electron oxygen reduction pathway.
• DFT calculations elucidated the roles of phenothiazine and amine groups in water oxidation and oxygen reduction, respectively.
• Cage architecture facilitated redox site separation and charge transport.

Conclusions:

• Covalent organic superphane cages are effective metal-free photocatalysts for sustainable H2O2 generation.
• SUPE-ptz-2 exhibits excellent photocatalytic efficiency, selectivity, and robustness.
• These singzymes offer a promising platform for solar-to-chemical conversion and environmental remediation.