Eutectic-Mediated Template-Free Synthesis of Mesoporous Single-Crystalline CdS for CO₂ Photoreduction

Efficient photocatalytic conversion of CO₂ into syngas is crucial for sustainable fuel production, yet conventional catalysts are often hampered by rapid charge recombination and insufficient surface area. Mesoporous single crystals (MSCs), which integrate a continuous single-crystal lattice with an open porous framework, offer a promising solution. Herein, we report a template-free strategy for synthesizing CdS MSCs in a NaOH-KOH-H₂O eutectic medium, yielding materials with tunable mesopore sizes (2.9-4.2 nm) and high surface areas (111-185 m²·g^-1). The optimized material achieves CO and H₂ evolution rates of 7019 and 4027 μmol·g^-1·h^-1, corresponding to 38- and 12-fold increases over bulk CdS. Notably, the H₂/CO ratio in the syngas product can be tuned by adjusting the cocatalyst dosage. The enhanced activity is attributed to the synergistic effects of large surface area, interconnected mesopores, and a continuous single-crystalline framework, which together facilitate charge separation and increase the density of accessible active sites. This work demonstrates a novel synthesis of mesoporous single-crystalline metal sulfides and establishes a generalizable strategy for designing high-performance photocatalysts. Its versatility is further evidenced by successful extension to NiO and Ni(OH)₂, among other materials, suggesting potential applicability to a broader range of compounds.