Evaluation of Efficient and Noble-Metal-Free NiTiO₃ Nanofibers Sensitized with Porous gC₃N₄ Sheets for Photocatalytic Applications

Abstract

One-dimensional nickel titanate nanofibers (NiTiO3 NFs) were synthesized and loaded with acetic acid-treated exfoliated and sintered sheets of graphitic carbon nitride (AAs-gC3N4) to fabricate a unique heterogeneous structure. This novel fabrication method for porous AAs-gC3N4 sheets using acetic acid-treated exfoliation followed by sintering provided gC3N4 with a surface area manifold larger than that of bulk gC3N4, with an abundance of catalytically active sites. Hybrid photocatalysts were synthesized through a two-step process. Firstly, NiTiO3 NFs (360 nm in diameter) were made by electrospinning, and these NiTiO3 NFs were sensitized with exfoliated gC3N4 sheets via a sonication process. Varying the weight ratio of NiTiO3 fibers to porous AAs-gC3N4 established that NiTiO3 NFs containing 40 wt% of porous AAs-gC3N4 exhibited optimal activity, i.e., removal of methylene blue and H2 evolution. After 60 min exposure to visible light irradiation, 97% of the methylene blue molecules were removed by the hybrid photocatalyst, compared with 82%, 72%, and 76% by pristine AAs-gC3N4, NiTiO3 NFs, and bulk gC3N4, respectively. The optimal structure also displayed excellent H2 evolution performance. The H2 evolution rate in the optimal sample (152 μmol g−1) was 2.2, 3.2 and 3-fold higher than that in pure AAs-gC3N4 (69 μmol g−1), NiTiO3 NFs (47 μmol g−1) and bulk gC3N4 (50 μmol g−1), respectively. This clearly shows that the holey AAs-gC3N4 nanosheets interacted synergistically with the NiTiO3 NFs. This extended the lifetime of photogenerated charge carriers and resulted in superior photocatalytic activity compared with pristine NiTiO3 NFs and bulk gC3N4. The higher Brunauer-Emmett-Teller surface area and the presence of many catalytically active sites also enhanced the photocatalytic performance of the hybrid sample. Moreover, through photoluminescence and photocurrent response analysis, a significant decrease in the recombination losses of the hybrid photocatalysts was also confirmed. Thus, this is a novel strategy to fabricate highly efficient photocatalysts with precisely tunable operating windows and enhanced charge separation.

Keywords

• NiTiO₃ NFs
• photocatalyst
• water treatment
• H₂ evolution
• gC₃N₄
• methylene blue