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

B and K co-doped g-C 3 N 4 , synthesized by molten salt method, exhibits the good photocatalytic performance for water vapor splitting and recycled molten salt was used for preparation of codoped g-C 3 N 4. • B and K co-doped g-C 3 N 4 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-C 3 N 4. • 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 O 2 from photocatalysts, the simultaneous generation of H 2 and O 2 is a critical challenge for water splitting. B and K co-doped g-C 3 N 4 (B/K-g-C 3 N 4) catalyst was synthesized by the recyclable molten-salt method in this study. Compared with the K doped and pristine g-C 3 N 4 samples, B/K-g-C 3 N 4 exhibited the highest photocatalytic activity for water vapor splitting under visible light illumination. The yield ratio of H 2 and O 2 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-C 3 N 4 sample demonstrated good photocatalytic stability after 9 cycles. Additionally, the co-doped g-C 3 N 4 catalyst, obtained from the repeatedly recyclable salts, still exhibited equivalent photocatalytic activity. Based on the built structure model with g-C 3 N 4 , 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-C 3 N 4 semiconductor was speculated. [ABSTRACT FROM AUTHOR]