The widespread use of antibiotics, particularly tetracycline, has led to severe water pollution worldwide. These persistent organic pollutants are difficult to degrade naturally and threaten aquatic ecosystems and human health by promoting bacterial resistance. Photocatalysis—a green technology that uses light to drive chemical reactions—offers a potential solution. However, traditional photocatalysts face three challenges: rapid recombination of photogenerated electron-hole pairs, narrow light absorption range, and poor stability.
In a study published in the KeAi journal Green Energy & Environment , a multidisciplinary team from Fuzhou University, Harvard University, MIT, and Sichuan University has developed a novel photocatalyst that directly tackles these challenges. The researchers engineered a hollow polyhedral bimetallic sulfide heterojunction (Co₉S₈/Ag₂S) derived from metal-organic framework (MOF) templates through a nanoconfinement strategy.
"The hollow architecture acts like a miniature light trap, allowing photons to reflect and scatter multiple times within the structure," explains Prof. Dr. Gao Xiao, the first author and corresponding author of the study. "This significantly enhances light harvesting efficiency. Meanwhile, the abundant mesopores provide fast diffusion pathways for pollutant molecules to reach active sites."
The researchers discovered that at the interface between Co₉S₈ and Ag₂S, a built-in electric field spontaneously forms. Density functional theory (DFT) calculations revealed that electrons tend to flow from Co₉S₈ to Ag₂S until a new equilibrium is established. This built-in electric field acts like a traffic police officer, directing photogenerated electrons to migrate directionally and suppressing recombination with holes.
"The Co₉S₈/Ag₂S heterojunction achieved a tetracycline degradation efficiency of 99.3% within 30 minutes under UV irradiation, with a kinetic rate constant of 0.152 min⁻¹ — five times higher than that of pristine Ag₂S," adds Xiao.
Notably, even in real water matrices such as tap water and lake water, the material maintained over 90% efficiency. After six consecutive cycles, the catalyst retained more than 75% of its initial activity, and XRD analysis confirmed no significant change in crystal structure.
"We also used electron spin resonance spectroscopy to directly capture the reactive species," says Xiao. "Both hydroxyl radicals (·OH) and superoxide radicals (·O₂⁻) were detected, confirming their crucial role in the degradation process."
The team further constructed a six-dimensional radar chart comparing monometallic and bimetallic heterojunction photocatalysts across cycle life, product yield, synergistic effect, light absorption, cost-effectiveness, and catalytic efficiency. The bimetallic Co₉S₈/Ag₂S system outperformed its monometallic counterparts in all dimensions, demonstrating a clear "1+1>2" synergy.
"We believe this rational design strategy — combining MOF self-templating, hollow architecture engineering, interfacial heterojunction construction, and nanoconfinement — provides a generalizable platform for developing high-performance photocatalysts for sustainable water treatment," Xiao says.
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Contact the author: Prof. Dr. Gao Xiao, College of Environment and Safety Engineering, Fuzhou University, Fuzhou 350108, Fujian, P. R. China.; John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA.; Division of Health Sciences & Technology, Harvard-Massachusetts Institute of Technology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA. Email: xiaogao@fzu.edu.cn
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Green Energy & Environment
Experimental study
Not applicable
Nanoconfinement Engineering of MOF-Derived-Hollow-Heterojunctions Towards Enhanced Photocatalysis
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.