Hexagonal Hollow Porous Organic Framework Nanotubes for Efficient Photocatalytic H2O2 Production in Pure H2O under O2 Atmosphere

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