Three-Dimensional Bicarbazole-Based Covalent Organic Frameworks as Efficient Yeager-Type Photocatalysts for H₂O₂...

Area of Science:

• Materials Science
• Photocatalysis
• Green Chemistry

Background:

• Photocatalytic conversion of oxygen to hydrogen peroxide (H2O2) is a promising solar-to-chemical pathway.
• Challenges include catalyst photocorrosion due to superoxide radicals (•O2-) and photoexcited holes (h+).
• Efficient and durable H2O2 production requires suppression of •O2- and consumption of h+.

Purpose of the Study:

• To develop a high-efficiency and durable H2O2 production system using a novel two-phase approach.
• To investigate metal-free 3D covalent organic framework (COF) photocatalysts for suppressing •O2- and consuming h+.
• To elucidate the reaction mechanisms involved in H2O2 photosynthesis and THIQ semidehydrogenation.

Main Methods:

• Development of a 1,2,3,4-tetrahydroisoquinoline (THIQ)-water two-phase system.
• Synthesis and application of 3D COFs (COF-BCTB-BT and COF-BCTB-TAPT) comprising bicarbazole (BCTB) and thiazole (BT) or triazine (TAPT) units.
• Theoretical calculations to determine reaction mechanisms and energy barriers.

Main Results:

• Achieved •O2--free direct two-electron oxygen reduction reaction (2e- ORR) to H2O2.
• Demonstrated a high H2O2 production rate of ~33.2 mmol gcat.-1 h-1 using COF-BCTB-BT.
• Efficient consumption of photoexcited h+ via THIQ semidehydrogenation (THIQ-SDR) to 3,4-dihydroisoquinoline (DHIQ).
• Theoretical calculations revealed a Yeager-type mechanism for 2e- ORR and THIQ-SDR.

Conclusions:

• The THIQ-water two-phase system effectively suppresses •O2- intermediates and consumes h+.
• High-efficiency and durable H2O2 photosynthesis was achieved using novel 3D bis-heterocyclic COF photocatalysts.
• This work presents an effective strategy for solar-driven H2O2 production, overcoming key catalytic challenges.