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.