Cellulose-Derived Hierarchical g-C₃N₄/TiO₂-Nanotube Heterostructured Composites with Enhanced Visible-Light...

A novel cellulose-derived hierarchical g-C₃N₄/TiO₂-nanotube heterostructured nanocomposite was fabricated by in situ coating thin g-C₃N₄ layers onto the surfaces of the TiO₂ nanotubes, which were synthesized by utilizing the natural cellulose substance (e.g., commercial ordinary filter paper) as the structural template. These g-C₃N₄/TiO₂-nanotube composites with varied thicknesses (ca. 3-30 nm) of the outer g-C₃N₄ layers displayed improved visible-light (λ > 420 nm)-driven photocatalytic degradation performances toward methylene blue. The optimal nanocomposite with an outer g-C₃N₄ layer of ca. 7.5 nm composed of 46 wt % g-C₃N₄ displayed an apparent rate constant of 0.0035 min^-1, which was 8.5- and 4-fold larger than those of the referential TiO₂-nanotube and g-C₃N₄ powder. The excellent and durable photocatalytic activities of these cellulose-derived g-C₃N₄/TiO₂-nanotube composites were ascribed to their hierarchically network porous structures replicated from the cellulose template, as well as the formation of close heterojunctions in-between the g-C₃N₄ and TiO₂ phases. Moreover, it was demonstrated that the photocatalytic mechanism matched with the type-II heterostructured model, while the main effective species during the photocatalytic processes of the nanocomposite were proved to be superoxide radicals.