A recyclable molten-salt synthesis of B and K co-doped g-C3N4 for photocatalysis of overall water vapor splitting

Highlights: • B and K co-doped g-C₃N₄ was synthesized by molten salt method. • The good photocatalytic performance for water vapor splitting was found. • Recycled molten salt was used for preparation of codoped g-C₃N₄. • Photocatalyst exhibited good cycling and stability. • Doped B and K accelerated the photoinduced electron-hole separation. Photocatalytic overall water splitting is one of the green and efficient energy technologies. Due to difficult release of O₂ from photocatalysts, the simultaneous generation of H₂ and O₂ is a critical challenge for water splitting. B and K co-doped g-C₃N₄ (B/K-g-C₃N₄) catalyst was synthesized by the recyclable molten-salt method in this study. Compared with the K doped and pristine g-C₃N₄ samples, B/K-g-C₃N₄ exhibited the highest photocatalytic activity for water vapor splitting under visible light illumination. The yield ratio of H₂ and O₂ reached approximately 2:1, and the corresponding rates were 1.18 and 0.58 μmol/h after 24 h of illumination. The B/K-g-C₃N₄ sample demonstrated good photocatalytic stability after 9 cycles. Additionally, the co-doped g-C₃N₄ catalyst, obtained from the repeatedly recyclable salts, still exhibited equivalent photocatalytic activity. Based on the built structure model with g-C₃N₄, the HOMO and LUMO distributions were changed by B and K co-doping, leading to improved separation of photoinduced carriers. The photocatalytic mechanism for water splitting over g-C₃N₄ semiconductor was speculated.