Research Highlights
This study combined theoretical calculations with experimental investigation to construct an S-scheme Cu₇S₄@ZnIn₂S₄ heterojunction rich in Cu and S dual vacancies. The research revealed the synergistic roles of the dual vacancies in enhancing the localized surface plasmon resonance (LSPR) effect, optimizing electron delocalization, and lowering the H⁺ adsorption energy barrier. Driven jointly by interfacial Cu–S bonds and the S-scheme charge-transfer mechanism, the separation efficiency of photogenerated hot electrons was greatly improved, ultimately delivering a hydrogen-evolution rate of 47.41 mmol·g−1·h−1 and a high apparent quantum efficiency of 52.6% at 500 nm.
Introduction
In January 2026, the Journal of Colloid and Interface Science published online the latest research achievement in photocatalytic hydrogen production from Professor Mengkui Tian’s team at Guizhou University. By combining theoretical simulations with experiments, the researchers constructed an S-scheme Cu₇S₄@ZnIn₂S₄ heterojunction featuring synergistic dual vacancies. Through regulation of the vacancy concentration, the LSPR effect was enhanced while the electronic structure was simultaneously optimized. DFT calculations and transient spectroscopy showed that Cu and S vacancies can serve as synergistic active sites, strengthening the local electromagnetic field and lowering the H⁺ adsorption energy barrier, thereby significantly improving photothermal-synergistic hydrogen-evolution activity. The first author is Dr. Mingkun Wu from the School of Chemistry and Chemical Engineering at Guizhou University, and the corresponding author is Professor Mengkui Tian.
Background
Solar-driven photocatalytic water splitting for hydrogen production provides a sustainable pathway for addressing global energy demand and environmental pollution. However, conventional photocatalysts are generally limited by narrow spectral-response ranges and severe recombination of photogenerated charge carriers, making it difficult for their overall energy-conversion efficiency to meet practical application requirements. In hydrogen-evolution reactions in particular, the slow adsorption and desorption kinetics of hydrogen intermediates and the rapid recombination of photogenerated electrons are key bottlenecks limiting further performance improvements.
In recent years, the localized surface plasmon resonance effect has created new opportunities to address these challenges because it can broaden the light-absorption range and generate high-energy hot electrons as well as localized thermal effects. Non-stoichiometric copper chalcogenides have attracted extensive attention due to their tunable plasmonic properties and abundant defect structures. Nevertheless, two major challenges remain. First, the mechanism by which the copper-vacancy concentration affects light absorption and hotspot distribution is still unclear. Second, the high-energy hot electrons produced by LSPR decay have extremely short lifetimes, ranging from femtoseconds to picoseconds, and their efficient extraction and utilization remain a major performance bottleneck.
To address these issues, this study coupled sulfur-vacancy-rich ZnIn₂S₄ with copper-vacancy-containing Cu₇S₄ to construct a dual-vacancy synergistic S-scheme heterojunction. By combining theoretical calculations with experimental analysis, the researchers systematically investigated how vacancy concentration influences the LSPR effect, electronic structure, and interfacial charge-transfer behavior. They further clarified the synergistic mechanism by which dual vacancies strengthen the local electromagnetic field, optimize the free energy of hydrogen adsorption, and promote directional hot-electron migration. This work not only reveals the origin of the LSPR effect in copper-deficient semiconductors but also provides new ideas and a theoretical basis for designing broad-spectrum, highly efficient plasmonic photocatalysts.
Equipment Used in the Study
Figure Analysis
Figure 1. Theoretical Calculations and Simulations: From Electromagnetic-Field Enhancement to Reaction-Kinetics Optimization
Key findings: FDTD simulations showed that the local electromagnetic-field intensity at the solid Cu₇S₄@Sv-ZIS interface reached 6.8, approximately three times that of pure CuS. DFT calculations confirmed that Cu and S dual vacancies increased the electron-transfer amount to 1.72 e and optimized the H⁺ adsorption free energy from −1.67 eV to −0.27 eV, close to the ideal value. The theoretical results indicate that dual vacancies can simultaneously enhance light absorption and reaction kinetics.
Figure 2. Morphological and Microstructural Characterization: Confirmation of Dual Vacancies and Interfacial Bonding
Key findings: TEM confirmed the successful construction of a core–shell structure consisting of Cu₇S₄ nanocubes measuring 200–300 nm coated with ZnIn₂S₄ nanosheets. HRTEM clearly revealed the formation of interfacial Cu–S bonds and lattice distortion, while EDS elemental mapping confirmed the coexistence of Cu and S vacancies at the heterointerface.
Figure 3. Phase Composition, Defects, and Photothermal Performance: Spectroscopic Evidence of Dual Vacancies
Key findings: EPR showed that the composite exhibited the strongest signal at g = 2.004, confirming enrichment of dual vacancies. In the FT-IR spectrum, the Cu–S vibration peak red-shifted from 613 to 642 cm−1, demonstrating interfacial chemical bonding. Photothermal imaging showed that the composite reached 58.3 °C, indicating that it retained excellent photothermal performance.
Figure 4. Band Structure and Charge-Transfer Mechanism: Experimental Confirmation of the S-Scheme Heterojunction
Key findings: In-situ XPS revealed that, in the dark, electrons flowed from Cu₇S₄ to Sv-ZIS, forming a built-in electric field. Under illumination, photogenerated electrons migrated in the opposite direction, consistent with an S-scheme mechanism. The band structure exhibited a staggered alignment, and the interfacial Cu–S bonds served as charge-transfer channels.
Figure 5. Photocatalytic Hydrogen-Evolution Performance: Record-Level Activity and Stability
Key findings: The optimized 4-C₇S₄Z catalyst achieved a hydrogen-evolution rate of 47.41 mmol·g−1·h−1, 11.6 times that of the pure components. Its apparent quantum efficiency reached 52.6% at 500 nm, and it retained 93% of its activity after five cycles. Its performance surpassed that of previously reported ZnIn₂S₄-based catalysts.
Figure 6. Ultrafast Charge-Carrier Dynamics: Femtosecond Transient Absorption Spectroscopy
Key findings: Femtosecond transient absorption spectroscopy revealed a characteristic hot-electron signal in the 800–900 nm region for the composite system. The lifetime reached 7,728 ps, substantially longer than the 669.6 ps observed for the pure phase, directly confirming that the S-scheme heterojunction suppresses charge-carrier recombination.
Conclusion
By combining theoretical simulations with experimental investigation, this study successfully constructed a core–shell S-scheme Cu₇S₄@ZnIn₂S₄ heterojunction photocatalyst rich in Cu and S dual vacancies. For the first time, it revealed the synergistic mechanism of copper and sulfur vacancies in enhancing the LSPR effect, optimizing electron delocalization, and lowering the H⁺ adsorption energy barrier. In-situ XPS and femtosecond transient absorption spectroscopy confirmed that interfacial Cu–S bonds and the built-in electric field drive S-scheme charge transfer. This mechanism both preserves the high-energy hot electrons generated by LSPR excitation and enables their spatial separation from holes, extending the hot-electron lifetime to 7,728 ps.
Under photothermal-synergistic conditions, the optimized catalyst achieved a hydrogen-evolution rate of 47.41 mmol·g−1·h−1 and an apparent quantum efficiency of 52.6% at 500 nm, placing its performance among the leading systems reported to date. The “dual-vacancy synergy plus S-scheme heterojunction” design concept proposed in this work not only provides a new strategy for plasmonic semiconductor photocatalysis but may also be extended to energy-catalysis applications such as CO₂ reduction, N₂ fixation, and organic synthesis. It has broad application prospects in low-cost hydrogen production, wastewater treatment, and fine-chemical manufacturing.
About the Author
Mengkui Tian is a professor and doctoral supervisor at the School of Chemistry and Chemical Engineering, Guizhou University. His main research interests include environmental materials, photocatalyst development, and waste treatment. He received his master’s degree from Guizhou University between 2000 and 2003 and completed doctoral training jointly at the Chinese Academy of Sciences and Shanghai Jiao Tong University between 2003 and 2007. From 2010 to 2011, he conducted postdoctoral research at the University of Tokyo in Japan. As first or corresponding author, he has published more than 70 papers in domestic and international journals, including Journal of Energy Chemistry, Nano Energy, Journal of Colloid and Interface Science, Separation and Purification Technology, Journal of Materials Chemistry A, International Journal of Hydrogen Energy, Applied Surface Science, and Rare Metals.
Reference Information
Mingkun Wu, Bingxian Chu, Bolin Hu, Jianjun Zhang, Wanliang Yang, Mengkui Tian*. “Unveiling the plasmonic electron origin: dual vacancies synergy in an S-scheme Cu₇S₄@ZnIn₂S₄ heterojunction boosting hot electron flow for photothermal H₂ evolution.” Journal of Colloid and Interface Science, 2026, 708, 139862.
https://doi.org/10.1016/j.jcis.2026.139862
Founded in 2006, Beijing Perfectlight Technology Co., Ltd. is a National High-Tech Enterprise, a Zhongguancun High-Tech Enterprise, and one of the first group of Beijing Specialized, Sophisticated, Distinctive, and Innovative Enterprises. The company has obtained ISO 9001, ISO 14001, and ISO 45001 management-system certifications, and its after-sales service has achieved the five-star standard under GB/T 27922-2011. Perfectlight specializes in the research, development, manufacturing, sales, and service of intelligent, high-precision, high-performance equipment and integrated solutions. Its product portfolio covers more than ten series, including light sources, photocatalytic, photoelectrocatalytic, photothermal and thermal catalytic systems, characterization and testing systems, pilot-scale and industrial research equipment, and photochemical synthesis systems. These products support the full R&D process from fundamental research and laboratory testing to pilot-scale development and industrial scale-up. Perfectlight serves universities, research institutes, and enterprises, with a focus on new energy, pharmaceutical synthesis, fine chemicals, and advanced materials. Its products are used in more than 3,000 laboratories and have been exported to nearly 50 countries, supporting the publication of more than 9,000 SCI-indexed papers. The company has led or participated in the formulation of national and industry standards, undertaken projects under the National Key Research and Development Program, and holds multiple core intellectual property rights and certifications for Beijing New Technologies and New Products. It has also helped multiple industrial customers establish photochemical production lines with annual capacities ranging from several tons to hundreds of tons.
