Synergistic design of dual S-scheme heterojunction CuO/NiAl-LDH@MIL-53(Fe) for boosting photocatalytic hydrogen evolution.

The development of heterojunctions is a proven strategy to augment the photocatalytic efficiency of materials. However, the enhancement in charge transfer facilitated by a single heterojunction is inherently constrained. To overcome these limitations, we synthesized a dual S-scheme heterojunction ternary composite photocatalyst, CuO/NiAl-LDH@MIL-53(Fe), designed for efficient visible-light-driven hydrogen (H) production. The composite catalyst demonstrated a remarkable H production rate of 2093.9 μmol·g·h, which is 4.0-fold greater than that of pristine CuO (530.5 μmol·g·h), 56.7-fold higher than that of NiAl-LDH (36.9 μmol·g·h), and 5.9-fold superior to the single S-scheme heterojunction NiAl-LDH@MIL-53(Fe) (353.8 μmol·g·h). The improved photocatalytic performance is ascribed to the synergistic electrostatic forces and coordination interactions between MIL-53(Fe) and in-situ grown NiAl-LDH, which establish a closely contacted interface. Additionally, the incorporation of CuO mitigates electron transfer resistance and diminishes the recombination rate of photogenerated charge carriers. The engineered dual S-scheme heterojunction significantly increases the charge transfer pathways for photogenerated charge carriers and introduces minimal interfacial resistance, thus achieving efficient charge transfer. Comprehensive experimental characterizations and density functional theory (DFT) calculations substantiate that the migration of photogenerated electrons adheres to the dual S-scheme heterojunction mechanism. This work provides a design concept that integrates a surface in-situ growth strategy with heterojunction engineering, offering a novel approach for the fabrication of advanced photocatalytic composite materials.