Multi-Energy-State Covalent Organic Framework/Sulfur-Vacancy-Engineered Mn_0.2Cd_0.8S S-Scheme Photocatalyst for...

Area of Science:

• Materials Science
• Photocatalysis
• Green Chemistry

Background:

• Hydrogen peroxide (H2O2) is a vital green oxidant, but its sustainable production via photocatalytic oxygen reduction reaction (ORR) is hindered by poor charge separation and carrier recombination.
• Existing single-component photocatalysts exhibit slow carrier dynamics, while multi-energy-state systems often suffer from recombination at intermediate states.
• S-scheme heterojunction engineering is a promising strategy to enhance charge transfer and maintain redox potentials for improved photocatalytic efficiency.

Purpose of the Study:

• To design and construct a novel S-scheme heterojunction photocatalyst for efficient solar-driven hydrogen peroxide production.
• To investigate the charge transfer dynamics and reaction mechanisms of the designed photocatalyst.
• To enhance the photostability and production rate of hydrogen peroxide.

Main Methods:

• Fabrication of an S-scheme photocatalyst by integrating a triazine-based covalent organic framework (COF) with sulfur-vacancy-rich Mn0.2Cd0.8S (Sv-MCS).
• Characterization using X-ray absorption fine-structure (XAFS) analysis to confirm interfacial coordination.
• In situ spectroscopies and density functional theory (DFT) calculations to elucidate reaction pathways and charge transfer mechanisms.
• Femtosecond transient absorption spectroscopy (fs-TAS) to investigate carrier dynamics and recombination suppression.

Main Results:

• The constructed S-scheme photocatalyst achieved a high H2O2 production rate of 5389.6 µmol·h−1·g−1 in pure water.
• XAFS analysis confirmed interfacial Cd-O coordination between the Sv-MCS and COF components.
• Spectroscopic and theoretical studies revealed a preferential two-electron ORR pathway and suppressed carrier recombination due to synergistic S-scheme charge transfer and interfacial bonding.
• Enhanced photostability of the catalyst was observed.

Conclusions:

• The developed dual-functional S-scheme photocatalyst effectively addresses charge separation and recombination issues, leading to high-efficiency solar-driven H2O2 production.
• The study establishes design principles for multi-energy-state S-scheme photocatalysts.
• This work represents a significant advancement in artificial photosynthesis for sustainable H2O2 generation.