Hierarchical Honeycomb Br-, N-Codoped TiO₂ with Enhanced Visible-Light Photocatalytic H₂ Production

Abstract

The halogen elements modification strategy of TiO₂ encounters a bottleneck in visible-light H₂ production. Herein, we have for the first time reported a hierarchical honeycomb Br-, N-codoped anatase TiO₂ catalyst (HM-Br,N/TiO₂) with enhanced visible-light photocatalytic H₂ production. During the synthesizing process, large amounts of meso-macroporous channels and TiO₂ nanosheets were fabricated in massive TiO₂ automatically, constructing the hierarchical honeycomb structure with large specific surface area (464 m² g^-1). cetyl trimethylammonium bromide and melamine played a key role in constructing the meso-macroporous channels. Additionally, HM-Br,N/TiO₂ showed a high visible-light H₂ production rate of 2247 μmol h^-1 g^-1, which is far more higher than single Br- or N-doped TiO₂ (0 or 63 μmol h^-1 g^-1, respectively), thereby demonstrating the excellent synergistic effects of Br and N elements in H₂ evolution. In HM-Br,N/TiO₂ catalytic system, the codoped Br-N atoms could reduce the band gap of TiO₂ to 2.88 eV and the holes on acceptor levels (N acceptor) can passivate the electrons on donor levels (Br donor), thereby preventing charge carriers recombination significantly. Furthermore, the proposed HM-Br,N/TiO₂ fabrication strategy had a wide range of choices for N source (e.g., melamine, urea, and dicyandiamide) and it can be applied to other TiO₂ materials (e.g., P25) as well, thereby implying its great potential application in visible-light H₂ production. Finally, on the basis of experimental results, a possible photocatalytic H₂ production mechanism for HM-Br,N/TiO₂ was proposed.