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Metal–organic frameworks MIL-88A hexagonal microrods as a new photocatalyst for efficient decolorization of methylene blue dye
Summary:
The authors from Laboratory of Advanced Porous Materials and School of Chemistry and Chemical Engineering, Anhui University, and National Synchrocyclotron Radiation Laboratory, University of Science and Technology of China developed MIL-88A hexagonal microrods, which have visible light response, high stability, and a large volume swelling effect in polar solvents, achieving efficient decolorization of methylene blue (MB) dye in the application of environmental purification.
Background:
1. To address the challenge of developing efficient, stable, and low-cost visible-light-responsive photocatalysts for pollutant degradation, previous researchers explored various photocatalysts such as TiO₂, ZnO, and some MOFs. While they showed certain activities, they had limitations like requiring UV excitation, photo-corrosion, or being in the infancy stage of photocatalytic properties.
2. The authors in this study proposed using MIL-88A as a new photocatalyst and found it has active performance for MB decolorization under visible light, with enhanced efficiency when adding H₂O₂ and good stability.
Research Content:
1. Synthesis:
The authors synthesized the MIL-88A photocatalyst by dissolving 5 mmol FeCl₃·6H₂O and 5 mmol fumaric acid in 25 mL ultrapure water, transferring the homogeneous solution into a 60 mL Teflon-lined stainless steel autoclave, heating to 65 °C for 12 h, then washing with water and ethanol, centrifuging, and drying in a vacuum oven.
2. Characterizations:
1) N₂ adsorption and desorption isotherms showed that due to the flexible structure being in a closed pore configuration after degassing, true physical parameters like surface area, pore size, and pore volume could not be obtained.
2) SEM and TEM tests show the particle size of the material: hexagonal microrods over 2 μm in length, less than 500 nm in diameter, with an average length of ~2.6 μm and width of ~500 nm, and relatively uniform size distribution.
3) Other tests: XRD analysis confirmed it is single-phase MIL-88A with an average crystallite size of ~24.7 nm; UV-vis spectrum showed absorption peaks with an absorption edge around ~650 nm and a band gap energy of 2.05 eV; VB XPS spectrum indicated the VB edge is at ~2.3 eV.
3. Application:
The material was tested in MB dye decolorization. Under visible light, ~16% MB was degraded in 20 min, which is 2 times higher than P25 TiO₂. With H₂O₂ addition, MB was completely degraded in 20 min, and no obvious activity loss was observed after four consecutive cycles.
4. Mechanism:
When MIL-88A is illuminated by visible light with energy ≥ its band gap, electrons are excited from the valence band to the conduction band, leaving holes. Holes can oxidize OH⁻ to generate •OH, and electrons can be trapped by O₂ to form •O₂⁻, both oxidizing MB. Adding H₂O₂ scavenges electrons, suppressing electron-hole recombination, increasing •OH generation, thus enhancing degradation efficiency.
Outlook:
This research demonstrates that MIL-88A hexagonal microrods are a promising visible-light-responsive photocatalyst for environmental purification, providing new insights into developing MOF photocatalysts and highlighting MOFs' potential in this field.
Metal–organic frameworks MIL-88A hexagonal microrods as a new photocatalyst for efficient decolorization of methylene blue dye
Authors: Wen-Tao Xu, Lin Ma, Fei Ke, Fu-Min Peng, Geng-Sheng Xu, Yu-Hua Shen, Jun-Fa Zhu, Ling-Guang Qiu, Yu-Peng Yuan
DOI: 10.1039/c3dt52574k
Link: https://pubs.rsc.org/en/content/articlelanding/2014/dt/c3dt52574k
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