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.