Construction of dual S-scheme heterojunctions g-C3N4/CoAl-LDH@MIL-53(Fe) ternary photocatalyst for enhanced photocatalytic H2 evolution

Abstract

The construction of dual-type heterojunction photocatalysts for efficient hydrogen (H₂) production through water splitting is a promising method in the field of photocatalysis. In this work, a ternary photocatalyst of g-C₃N₄/CoAl-LDH@MIL-53(Fe) with a dual S-scheme heterojunction was prepared for the first time. This composite demonstrates outstanding photocatalytic performance under visible light, reaching as high as H₂ production rate of 1222.2 µmol·g⁻¹·h⁻¹ for the optimized g-C₃N₄/CoAl-LDH₄₀@MIL-53(Fe)₍₆₀₎, which was 7.1 times higher than that of the single heterojunction CoAl-LDH₄₀@MIL-53(Fe). The dual heterojunction design narrows the bandgap, increases photocurrent density, and reduces photoluminescence intensity, thereby improving visible light absorption and charge carrier separation. MIL-53(Fe) serves as excellent electron donor, while CoAl-LDH and g-C₃N₄ act as electron acceptors, which synergistically facilitate electron transfer in CoAl-LDH@MIL-53(Fe). Furthermore, the tight contact interface of g-C₃N₄/CoAl-LDH@MIL-53(Fe) establishes a dual S-scheme charge carrier transfer pathway with abundant active sites which are pivotal for the efficient separation of electrons and holes. A plausible mechanism for the photocatalytic water splitting to H₂ was proposed, elucidating the role of the dual S-scheme heterojunction in boosting H₂ production. Current work provides a promising strategy for fabricating dual heterojunction photocatalyst to achieve efficient photocatalytic H₂ evolution.