Efficient degradation of high concentration azo-dye wastewater by heterogeneous Fenton process with iron-based metal-organic framework

• High surface area FeII@MIL-100(Fe) as Fenton catalyst was used to remove 500 ppm MB.
• Electrostatic attraction greatly influenced MB adsorption over different MOFs.
• MOF-based catalysts presented much higher TOF value than traditional iron oxides.
• Reasonable activation mechanism was proposed to explain Fenton oxidation activity.

A novel iron-based metal-organic framework, possessing high surface area and good catalytic activity, was proposed as a heterogeneous Fenton catalyst for degrading high concentration methylene blue (CMB = 500 ppm). The morphology and physicochemical properties of prepared catalysts were characterized by SEM, XRD, XPS, FT-IR, Raman spectra, etc. The obtained results showed that MOF-based catalysts MIL-100(Fe) and FeII@MIL-100(Fe) possess high surface area of 1646 and 1228 m2 g−1, respectively. The MB removal though adsorption by MIL-100(Fe) and FeII@MIL-100(Fe) is respectively 27 and 6% in 30 min, due to the electrostatic interaction between negative (or positive) adsorbent and positive pollutant. However, FeII@MIL-100(Fe) exhibited highest Fenton catalytic ability compared to MIL-100(Fe) and Fe2O3 catalysts. The catalytic activity of each active site, evaluated by the turn over frequency (TOF) value, varied in the order of FeII@MIL-100(Fe) > MIL-100(Fe) > Fe2O3. The main role of determining the decomposition efficiency, i.e., hydroxyl radical (OH) generation, surface redox properties and surface reaction, was greatly enhanced by the synergistic effect between FeII and FeIII in FeII@MIL-100(Fe). Moreover, iron-based metal-organic framework retained the catalytic performance in a wide pH range of 3–8, and had a relative low iron leaching even in acidic condition.

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