A Dimolybdenum Paddlewheel Embedded Covalent Organic Framework for Photocatalytic Hydrogen Peroxide Generation.

In the midst of the global energy crisis, the conversion of solar energy into chemical energy or high-value chemicals has become critical. Hydrogen peroxide (H2O2), a versatile oxidizing agent, plays an important role in chemical synthesis, medical disinfection, and clean energy generation via fuel cells. Recently, photocatalytic H2O2 generation from water and oxygen using covalent organic frameworks (COFs) and metal-organic frameworks (MOFs) has emerged as a sustainable approach. In this context, a novel dimolybdenum paddlewheel-embedded COF (Mo-DHTA COF) is presented and synthesized for photocatalytic H2O2 generation. It is observed that Mo sites help to bind the oxygen molecule, while high-energy valence band electrons localized on the α-hydroquinone moiety of the COF facilitate efficient photoelectron transfer for oxygen reduction. Simultaneously, the reduced electron density above the hydroxy groups in the conduction band serves as a proton source during H2O2 production. Due to these synergistic effects, Mo-DHTA COF exhibited an H2O2 production rate of 626 µmol g-1 h-1 in aqueous ethanol and 4084 µmol g-1 h-1 in aqueous benzyl alcohol, which is found to be higher than the polymeric counterpart of Mo-DHTA (Mo-DHTA-P). This innovative design highlights the potential of metal-embedded crystalline and porous COFs for advanced photocatalytic applications.