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Functionalized MIL-53(Fe) as efficient adsorbents for removal of tetracycline antibiotics from aqueous solution
Summary:
The authors from College of Environmental Science and Engineering, Hunan University and Key Laboratory of Environmental Biology and Pollution Control (Hunan University) developed functionalized MIL-53(Fe) (including NH₂-MIL-53(Fe), NO₂-MIL-53(Fe), Br-MIL-53(Fe)) with characteristics such as high adsorption capacity, good reusability, and stable performance, achieving excellent results in the application of tetracycline (TCN) removal from aqueous solution.
Background:
1. Antibiotic pollution, especially tetracycline, is a serious environmental problem. Existing removal methods like electrochemical and biological methods have deficiencies such as secondary pollution or low efficiency. Adsorption is superior but lacks high-performance adsorbents with good selectivity and stability.
2. The authors proposed introducing functional groups (-NH₂, -NO₂, -Br) into MIL-53(Fe) via a one-step solvothermal method to enhance its adsorption performance for TCN, obtaining efficient adsorbents.
Research Content:
1. Synthesis:
The authors synthesized MIL-53(Fe) and functionalized MIL-53(Fe) using the solvothermal method. For MIL-53(Fe), FeCl₃·6H₂O and terephthalic acid (H₂BDC) were mixed in DMF, stirred, and heated in a Teflon-lined autoclave at 170 °C for 24 h, followed by washing and drying. NH₂-MIL-53(Fe), NO₂-MIL-53(Fe), and Br-MIL-53(Fe) were synthesized similarly by replacing H₂BDC with 2-aminoterephthalic acid, nitro-terephthalic acid, and 2-bromoterephthalic acid, respectively.
2. Characterizations:
1) BET, pore size distribution: MIL-53(Fe) has a BET surface area of 52.18 m²/g, pore size of 8.81 nm, and total pore volume of 0.115 cm³/g; NH₂-MIL-53(Fe) has 65.64 m²/g, 3.80 nm, 0.314 cm³/g; NO₂-MIL-53(Fe) has 30.01 m²/g, 4.85 nm, 0.243 cm³/g; Br-MIL-53(Fe) has 39.75 m²/g, 4.07 nm, 0.107 cm³/g.
2) SEM tests: MIL-53(Fe) is rod-like with an average width of 10 μm; NH₂-MIL-53(Fe) and NO₂-MIL-53(Fe) are bipyramidal hexagonal prisms with smooth surfaces; Br-MIL-53(Fe) is a cubic octahedron with a smooth surface.
3) Other tests: XRD confirmed the framework structure of all samples was maintained after functionalization; FTIR identified characteristic functional groups, such as -NH₂, -NO₂, and Fe-O bonds.
3. Application:
- Adsorption of TCN: Br-MIL-53(Fe) has the highest maximum adsorption capacity of 309.6 mg/g.
- Effects of factors: The adsorption is affected by pH, co-existing ions (NaCl, CaCl₂), and humic acid, with higher temperatures promoting adsorption.
- Reusability: After 4 cycles, the adsorption capacity remains nearly 80% using ethanol as eluent.
4. Mechanism:
The adsorption kinetics fit the pseudo-second order model, indicating chemisorption is dominant. The isotherms fit the Langmuir model, suggesting monolayer adsorption on a homogeneous surface. Thermodynamics show the process is spontaneous and endothermic. Mechanisms include π-π interaction, hydrogen bonding (for NH₂-MIL-53(Fe)), acid-base interaction (for NO₂/Br-MIL-53(Fe)), and the breathing feature of Br-MIL-53(Fe) which increases pore size to accommodate more TCN.
Outlook:
This research successfully prepares functionalized MIL-53(Fe) with high TCN adsorption capacity and good reusability, providing an effective strategy for antibiotic wastewater treatment and expanding the application of MOFs in environmental remediation.
Functionalized MIL-53(Fe) as efficient adsorbents for removal of tetracycline antibiotics from aqueous solution
Authors: Jun Yu, Weiping Xiong, Xin Li, Zhaohui Yang, Jiao Cao, Meiying Jia, Rui Xu, Yanru Zhang
DOI: 10.1016/j.micromeso.2019.109642
Link: https://doi.org/10.1016/j.micromeso.2019.109642
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