Ice-Assisted Synthesis of Black Phosphorus Nanosheets as a Metal-Free Photocatalyst: 2D/2D Heterostructure for Broadband H2 Evolution

A 2D/2D heterojunction of black phosphorous (BP)/graphitic carbon nitride (g-C3N4) is designed and synthesized for photocatalytic H-2 evolution. The ice-assisted exfoliation method developed herein for preparing BP nanosheets from bulk BP, leads to high yield of few-layer BP nanosheets (approximate to 6 layers on average) with large lateral size at reduced duration and power for liquid exfoliation. The combination of BP with g-C3N4 protects BP from oxidation and contributes to enhanced activity both under lambda > 420 nm and lambda > 475 nm light irradiation and to long-term stability. The H-2 production rate of BP/g-C3N4 (384.17 mu mol g(-1) h(-1)) is comparable to, and even surpasses that of the previously reported, precious metal-loaded photocatalyst under lambda > 420 nm light. The efficient charge transfer between BP and g-C3N4 (likely due to formed NP bonds) and broadened photon absorption (supported both experimentally and theoretically) contribute to the excellent photocatalytic performance. The possible mechanisms of H-2 evolution under various forms of light irradiation is unveiled. This work presents a novel, facile method to prepare 2D nanomaterials and provides a successful paradigm for the design of metal-free photocatalysts with improved charge-carrier dynamics for renewable energy conversion.