Hexagonal\nHollow Porous Organic Framework Nanotubes\nfor Efficient Photocatalytic H₂O₂ Production\nin Pure H₂O under O₂ Atmosphere

Abstract

The production of hydrogen peroxide (H₂O₂) by combining photocatalytic oxygen (O₂) reduction\nwith\nwater (H₂O) oxidation is a satisfactory substitute for\nthe industrial anthraquinone process. But the photocatalytic efficiency\nof H₂O₂ generation is still low, especially\nin heterogeneous reactions, owing to the poor mass transfer and weak\nH₂O oxidation. Hereby, a porous organic framework (BPYTEA-POF)\nwith a hexagonal hollow nanotube structure was synthesized through\n5,5′-dibromo-2,2′-bipyridine (BPY) reacting with tris(4-ethynylphenyl)amine\n(TEA) by the Sonogashira coupling reaction without a template, which\ncontains a 2,2′-bipyridine H₂O oxidation active\nsite. BPYTEA-POF with hexagonal hollow nanotube morphology and a hierarchical\nporous wall is beneficial to the mass transfer and/or diffusion of\nthe substrate via a siphonic effect; meanwhile, it benefits exposure\nof the catalytic active site, which boosts the contact of O₂ and H₂O with the active site and rapidly dissociates\nthe generated H₂O₂, thus improving the photocatalytic\nreaction efficiency. At the same time, the 2,2′-bipyridine\nmoiety is capable of effectually weakening the O–H bonds of\nH₂O and promoting the oxidation of H₂O to produce\nO₂ and proton (H⁺); then, the produced O₂ and H⁺ were used for efficient H₂O₂ production under additive-free condition. The definite hollow\nnanotube structure and specific active sites of H₂O oxidation\nenhance the initial photocatalytic rate of O₂ and H₂O to H₂O₂ by BPYTEA-POF up to 3446 μmol\ng_cat^–1 h^–1, under the\ncondition of visible-light irradiation (λ ≥ 400 nm) without\nany additional additive.