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Ultrathin graphene oxide encapsulated in uniform MIL-88A(Fe) for enhanced visible light-driven photodegradation of RhB
Summary:
The authors from University of Shanghai for Science and Technology, Shanghai University, and Taizhou Vocation & Technical College developed M88/GO nanocomposites (ultrathin graphene oxide encapsulated in MIL-88A(Fe)) with high surface area, good visible light absorption, and excellent stability, achieving enhanced visible light-driven photodegradation of organic pollutants like Rhodamine B (RhB) in environmental purification.
Background:
1. Metal-organic frameworks (MOFs) have potential in photocatalysis but suffer from poor separation of photogenerated electron-hole pairs. Previous strategies like noble metal doping are limited by high cost, and some MOFs use DMF as solvent causing secondary contamination.
2. The authors proposed a one-pot hydrothermal method to synthesize DMF-free MIL-88A(Fe)/graphene oxide (M88/GO) composites, which significantly enhanced photocatalytic efficiency by improving charge separation and surface area.
Research Content:
1. Synthesis:
The authors synthesized M88/GO nanocomposites using a one-pot hydrothermal method. GO was prepared by modified Hummers method, MIL-88A(Fe) by hydrothermal reaction of FeCl₃·6H₂O and fumaric acid (C₄H₄O₄) in water, and M88/GO by mixing GO solution with FeCl₃·6H₂O and fumaric acid, followed by hydrothermal treatment at 65 °C for 12 h.
2. Characterizations:
1) BET surface area of M88/GO-9 (optimal GO content 9 wt%) is 408.9 m²/g, with pore size distribution of 1.12/2.60-3.21 nm, much higher than pure MIL-88A(Fe) (15.9 m²/g, 3.76 nm).
2) SEM/TEM tests show M88/GO-9 has needle-shaped microrods (1-3 μm length, 200-500 nm diameter) with GO evenly wrapping the surface.
3) Other tests: XRD confirms structure; FT-IR indicates preserved functional groups; XPS shows Fe(III) with shifted binding energy due to GO interaction; UV-vis DRS reveals narrowed band gap (2.19 eV vs 2.58 eV of MIL-88A(Fe)) and enhanced visible light absorption; Mott-Schottky plot shows it's an n-type semiconductor with conduction band -0.70 V vs NHE and valence band 1.49 V vs NHE.
3. Application:
The material was tested in photodegradation of RhB, phenol, methyl blue (MB), and methyl orange (MO). Under optimal conditions (0.4 g/L M88/GO-9, 20 mM H₂O₂, visible light), RhB (10 mg/L) is almost completely degraded within 80 min, with a pseudo-first-order rate constant (0.0645 min⁻¹) 8.4 times that of pure MIL-88A(Fe). It also degrades 95.8% phenol, 92.0% MB, and 93.2% MO, and maintains ~100% RhB removal after 5 cycles.
4. Mechanism:
Under visible light, M88/GO-9 generates e⁻ and h⁺. GO acts as electron acceptor, accelerating e⁻/h⁺ separation. e⁻ reacts with H₂O₂ to produce ·OH and with O₂ to form ·O₂⁻; Fe(III)-O clusters in MIL-88A(Fe) catalyze H₂O₂ via Fenton-like reaction to generate ·OH; h⁺ directly oxidizes pollutants. These active species (·OH, ·O₂⁻, h⁺) degrade RhB synergistically.
Outlook:
This research successfully fabricates high-performance M88/GO composites via a simple method, providing a new approach for designing efficient, stable, and environment-friendly MOF-based photocatalysts for environmental pollutant degradation.
Ultrathin graphene oxide encapsulated in uniform MIL-88A(Fe) for enhanced visible light-driven photodegradation of RhB
Authors: Ning Liu, Wenyuan Huang, Xiaodong Zhang, Liang Tang, Liang Wang, Yuxin Wang, Minghong Wu
DOI: 10.1016/j.apcatb.2017.09.020
Link: https://www.sciencedirect.com/science/article/pii/S0926337317308597
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