Pulsed Laser Engineering of Sulfur Defects in ZnIn2S4 Boosts CO2 Reduction

Scientists are racing to mimic photosynthesis by turning carbon dioxide (CO₂) into fuels and chemicals using sunlight. A major bottleneck in photocatalysis is finding materials that are both efficient and stable at converting CO₂ while resisting rapid charge-carrier losses inside the catalyst. Now, a collaborative team from the University of Science and Technology of China and partner institutions reports a defect-engineering strategy that dramatically boosts performance in a leading photocatalyst family.

The work focuses on ZnIn₂S₄ nanosheets, a semiconductor that can drive CO₂ reduction under light but typically suffers from limited absorption and fast recombination of photogenerated electrons and holes. Instead of relying on conventional defect-creation methods that may require harsh reagents or high-temperature processing, the researchers used pulsed laser ablation in liquid (PLAL). This approach is performed in water at room temperature and is designed for precise, tunable modification of the material’s defect landscape.

In their method, high-energy laser pulses strike a suspension of ZnIn₂S₄ nanosheets. The intense, localized energy ejects sulfur atoms from the crystal lattice, generating sulfur vacancies while preserving the overall nanosheet integrity. Crucially, the team demonstrated that irradiation time controls the defect density, allowing systematic tuning rather than one-size-fits-all defect introduction.

Advanced spectroscopy and microscopy confirmed that the engineered vacancies introduce mid-gap electronic states, extending light absorption into the visible range. At the same time, the vacancies act as electron traps, which suppress electron–hole recombination—one of the dominant causes of performance loss in photocatalytic CO₂ reduction.

The researchers describe sulfur vacancies as a “triple function”: enhanced light harvesting, improved charge separation and carrier lifetime, and creation of highly active adsorption sites that can capture and activate inert CO₂ molecules. This combination targets multiple steps of the reaction rather than optimizing only one.

With the optimal PLAL treatment (1.5 hours, labeled ZIS-D₁.₅h), the catalyst delivered a CO production rate of 365 μmol g⁻¹ h⁻¹ with high selectivity (89%). The defective structure also retained strong activity across multiple reaction cycles, indicating that the laser-created defects are stable enough for repeated use.

To verify the reaction pathway, the team performed isotope labeling using ¹³CO₂. The isotopic experiments showed that the produced CO originates from the supplied CO₂ feed rather than from contamination or background sources. They further supported mechanistic claims with theoretical calculations showing that sulfur vacancies lower the energy barrier of the key rate-limiting step, the formation of the *COOH intermediate from adsorbed CO₂.

Overall, the study positions PLAL as a green, scalable platform for precision defect engineering in next-generation photocatalysts. The authors suggest the same principles could be extended to other materials to help build more effective artificial photosynthesis systems.

Keywords

photocataysis; CO₂-to-CO; ZnIn₂S₄; sulfur vacancies; PLAL; defect engineering; charge separation; visible-light absorption; isotope labeling