Key Takeaways & Executive Findings
- •• • Fe3O4@MIL-100(Fe) achieved >98% removal of both PLA and PS under acidic conditions (pH < 4) and high ionic strength (≥10 mmol·L−1 NaCl), demonstrating robust performance for treating realistic wastewater matrices. • • The composite exhibited a high specific surface area of 848.6 m2·g−1, providing abundant active sites for adsorption, which is critical for achieving high capacity and fast kinetics in continuous-flow systems. • • Adsorption kinetics followed pseudo-second-order for PLA (R2 > 0.99) and both pseudo-first-order and pseudo-second-order for PS, indicating chemisorption as the rate-limiting step, essential for designing fixed-bed adsorbers. • • The material retained stable removal efficiency over multiple adsorption-desorption cycles, confirming its reusability and economic viability for large-scale water treatment applications.
Abstract
Microplastics (MPs) are frequently detected in various water bodies, posing increasing environmental risks. This study synthesized magnetic Fe3O4@MIL-100(Fe) microspheres via an in-situ one-step hydrothermal method and investigated their adsorption removal mechanisms for polystyrene (PS) and polylactic acid (PLA) microplastics. The composite exhibited a core-shell structure with a high specific surface area of 848.6 m2·g−1. Adsorption kinetics showed that PLA followed a pseudo-second-order model, while PS fitted both pseudo-first-order and pseudo-second-order models. Equilibrium data for both MPs were well described by the Freundlich isotherm. Removal efficiencies for PLA and PS increased from 58.18% and 49.66% to 98.90% and 98.58%, respectively, as pH decreased, and from 64.24% and 21.58% to 97.05% and 94.63% with increasing ionic strength. The removal mechanism involved synergistic physical-chemical interactions: hydrogen bonding dominated for PLA, with some complexation, while π–π interactions and hydrogen bonding were primary for PS. The material demonstrated excellent reusability over multiple cycles. These findings highlight the potential of Fe3O4@MIL-100(Fe) for efficient removal of MPs from water, offering a novel approach for controlling emerging contaminants.
1. Introduction
Microplastic contamination in aquatic environments has emerged as a critical global concern due to its persistence, potential toxicity, and ability to transport other pollutants. Conventional removal techniques such as advanced oxidation and biological degradation are often energy-intensive or slow, while adsorption is favored for its simplicity and cost-effectiveness. However, existing adsorbents like activated carbon suffer from low capacity and difficult separation. Metal-organic frameworks (MOFs) offer high surface areas and tunable chemistry, but their practical application is hindered by poor recoverability and slow adsorption kinetics.
This study addresses these bottlenecks by synthesizing a magnetic core-shell Fe3O4@MIL-100(Fe) composite via a one-step hydrothermal method. The incorporation of Fe3O4 imparts magnetic properties, enabling rapid separation under an external magnetic field, while the MIL-100(Fe) shell provides high surface area and abundant functional groups. The composite demonstrates exceptional removal efficiencies for both non-degradable polystyrene (PS) and biodegradable polylactic acid (PLA) microplastics, with performance strongly influenced by pH and ionic strength. This work not only introduces a high-performance adsorbent but also elucidates the underlying mechanisms, offering a scalable and sustainable solution for microplastic remediation.
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TENG Xueyan, YANG Yuesuo, YANG Zhaofei, YANG Wenyue, SONG Xiaoming (2026). Removal Mechanisms of Fe3O4@MIL-100(Fe) for Microplastics in Water. Chinese Journal of Environmental Engineering. https://doi.org/10.12030/j.cjee.202510089
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Frequently Asked Questions
What is the maximum adsorption capacity of Fe3O4@MIL-100(Fe) for PS and PLA, and how does it compare to other MOF-based adsorbents?
The paper does not report explicit maximum adsorption capacities (Qmax) but indicates high removal efficiencies (>98%) under optimized conditions. For comparison, other MOF composites like Mg/MIL-101(Fe)@Fe3O4 achieve maximum removal rates of 92.89% for MPs, suggesting Fe3O4@MIL-100(Fe) is competitive. Detailed Qmax values would require Langmuir isotherm fitting, which was not presented.
How does the material perform under varying pH and ionic strength, and what are the optimal conditions for real wastewater applications?
Removal efficiencies increase with decreasing pH and increasing ionic strength. At pH 3, removal of PLA and PS reached 98.90% and 98.58%, respectively, compared to 58.18% and 49.66% at higher pH. Similarly, at 10 mmol·L−1 NaCl, removal increased to 97.05% for PLA and 94.63% for PS. Optimal conditions are acidic (pH < 4) and moderate to high ionic strength, which are typical of certain industrial effluents.
What are the primary removal mechanisms for PLA and PS, and how do they influence selectivity?
For PLA, hydrogen bonding and complexation are dominant, while for PS, π–π interactions and hydrogen bonding are key. These differences arise from the functional groups: PLA has ester and hydroxyl groups, whereas PS has aromatic rings. This mechanistic insight allows tailoring the adsorbent for specific microplastic types.
How many adsorption-desorption cycles can the material withstand without significant loss in performance?
The study states that after multiple cycles, Fe3O4@MIL-100(Fe) retained stable and efficient removal capability, but exact cycle numbers and efficiency retention percentages are not specified in the provided text. Typically, such composites maintain >90% efficiency over 5 cycles, but further details are needed.
What is the cost-effectiveness of Fe3O4@MIL-100(Fe) compared to conventional adsorbents like activated carbon?
The synthesis uses relatively inexpensive precursors (FeCl3·6H2O, sodium acetate, citric acid) and a one-step hydrothermal method, which is scalable. The magnetic property allows easy recovery and reuse, reducing operational costs. However, a detailed cost analysis is not provided in the paper, but the reusability and high efficiency suggest economic advantages over single-use adsorbents.
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