Key Takeaways & Executive Findings
- •• • Bacterial/Fe3O4 hybrid materials achieved significantly higher gallic acid degradation rates than Fe3O4 alone, with hydroxyl radicals showing the highest correlation (r = 0.98) to the degradation rate constant, confirming their dominant role in the oxidative pathway. • • Electroactive bacteria promote the formation of oxygen vacancies (OVs) on Fe3O4 surfaces, which are positively correlated with ROS generation, thereby accelerating electron transfer and enhancing catalytic efficiency. • • The optimal temperature range for gallic acid degradation was 30–40 °C, attributed to bacterial temperature sensitivity, indicating a trade-off between bacterial activity and catalytic performance. • • The hybrid system generates multiple ROS species (hydroxyl radicals, superoxide radicals, and singlet oxygen), with hydroxyl radicals identified as the primary species responsible for degradation, as verified by quenching experiments.
Abstract
Iron-based catalysts are widely used in water pollution treatment due to their high stability and redox capabilities. However, conventional single-component iron-based catalytic systems face challenges such as slow reaction kinetics and low efficiency in generating reactive oxygen species (ROS) during organic pollutant degradation. In this study, three electroactive bacteria (Bacillus megaterium, Lactococcus lactis, and Shewanella putrefaciens) were selected to interact with nano-Fe3O4 to construct bacterial/Fe3O4 hybrid materials, accelerating the degradation of gallic acid. The results showed that bacterial interaction with Fe3O4 facilitated rapid electron transfer, enhancing gallic acid degradation. The bacterial/Fe3O4 hybrid materials exhibited significantly higher gallic acid degradation rates compared to Fe3O4 alone. This improvement was mainly attributed to the ability of electroactive bacteria to promote the formation of oxygen vacancies (OVs) on the Fe3O4 surface, accelerating electron transfer and subsequently enhancing the generation of ROS, including hydroxyl radicals, superoxide radicals, and singlet oxygen. Correlation analysis demonstrated a significant positive relationship between OVs and ROS generation, with hydroxyl radicals showing the highest correlation with the gallic acid degradation rate constant (r = 0.98), indicating its dominant role in gallic acid degradation; the hydroxyl radicals quenching experiment also verified its dominant role. Additionally, due to the temperature sensitivity of bacteria, the degradation rate of gallic acid reached its peak in the temperature range of 30–40 °C. This study reveals the mechanism by which electroactive bacteria enhance the catalytic activity of Fe3O4, providing a new strategy for its application in advanced oxidation technology for water pollution treatment.
1. Introduction
Conventional iron-based catalytic systems, while stable and redox-active, suffer from sluggish kinetics and insufficient reactive oxygen species (ROS) generation when degrading organic pollutants in water. This bottleneck limits their practical application in advanced oxidation processes, particularly for recalcitrant small-molecule organic acids like gallic acid, which can form carcinogenic disinfection byproducts during chlorination.
This study addresses the limitation by integrating electroactive bacteria with nano-Fe3O4 to form hybrid materials. The bacterial component enhances electron transfer and promotes the formation of oxygen vacancies on the Fe3O4 surface, thereby increasing ROS production and accelerating pollutant degradation. This bio-inorganic hybrid strategy offers a novel approach to overcome the kinetic and efficiency barriers of traditional iron-based catalysts.
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WANG Xuyang, ZHENG Yu, WU Min, DU Wei, LI Shunling, PAN Bo (2026). Electroactive Bacteria Accelerate the Degradation of Gallic Acid by Nano Iron Minerals and Its Mechanism. Environmental Chemistry. https://doi.org/10.7524/j.issn.0254-6108.2025021602
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Frequently Asked Questions
What is the mechanism by which electroactive bacteria enhance the catalytic activity of Fe3O4?
Electroactive bacteria interact with Fe3O4 to promote the formation of oxygen vacancies (OVs) on the Fe3O4 surface. These OVs facilitate rapid electron transfer, which in turn enhances the generation of reactive oxygen species (ROS) such as hydroxyl radicals, superoxide radicals, and singlet oxygen. The increased ROS production accelerates the degradation of gallic acid.
What is the optimal temperature range for gallic acid degradation using the bacterial/Fe3O4 hybrid system?
The optimal temperature range is 30–40 °C. This is attributed to the temperature sensitivity of the bacteria, which likely exhibit maximum metabolic activity in this range, thereby enhancing electron transfer and ROS generation.
Which reactive oxygen species plays the dominant role in gallic acid degradation?
Hydroxyl radicals (•OH) play the dominant role, as indicated by the highest correlation coefficient (r = 0.98) with the degradation rate constant. This was further confirmed by hydroxyl radical quenching experiments.
How does the degradation rate of gallic acid with the hybrid material compare to that with Fe3O4 alone?
The bacterial/Fe3O4 hybrid materials exhibited significantly higher gallic acid degradation rates compared to Fe3O4 alone, demonstrating the synergistic effect of the bacteria in enhancing catalytic performance.
What is the significance of oxygen vacancies in the catalytic process?
Oxygen vacancies are positively correlated with ROS generation. They act as active sites that facilitate electron transfer, leading to increased production of ROS and thus higher degradation efficiency.
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