Construction of core-shell magnetic metal-organic framework composites Fe3O4@MIL-101(Fe, Co) for degradation of RhB by efficiently activating PMS

Abstract

Low catalytic efficiency and catalyst recovery are the key factors limiting the practical application of advanced oxidation processes. In this work, a core-shell magnetic nanostructure Fe₃O₄@MIL-101(Fe, Co) was prepared via a simple solvothermal method. The core-shell structure and magnetic recovery performance were characterized by various technologies. The results of dye degradation experiments proved that within 10 minutes, the Fe₃O₄@MIL-101(Fe, Co)/PMS system can degrade more than 95% of 10 mg per L Rhodamine (RhB) at an initial pH of 7, which possesses higher catalytic activity than the Fe₃O₄/PMS system and the MIL-101(Fe, Co)/PMS system. The effects of initial solution pH and coexisting anions in water on the degradation of RhB were further discussed. The results showed that Fe₃O₄@MIL-101(Fe, Co) displayed excellent degradation efficiency in a wide pH range of 3-11 and capability of resisting coexisting anions. It is worth mentioning that after five cycles, the RhB removal rate can still be maintained at over 90% after 10 minutes of reaction. Free radical quenching experiments were further studied, confirming that ˙OH and SO₄^-˙ were involved in the degradation of RhB, while the dominating active free radical was SO₄^-˙. The possible reaction mechanism of the RhB degradation process was also inferred.

Scheme 1. Schematic illustration of synthetic procedure of Fe₃O₄@MIL-101(Fe, Co) for PMS activation.

Fig. 1. (a) XRD of Fe₃O₄@MIL-101(Fe, Co), MIL-101(Fe, Co) and Fe₃O₄; (b) FT-IR of Fe₃O₄@MIL-101(Fe, Co), MIL-101(Fe, Co) and Fe₃O₄.

Fig. 2. SEM images of Fe₃O₄@MIL-101(Fe, Co) (a and b); the EDX spectrum of Fe₃O₄@MIL-101(Fe, Co) (c) HRTEM image of Fe₃O₄@MIL-101(Fe, Co) (d–f); changes of Fe₃O₄@MIL-101(Fe, Co) before and after magnetic field application (g).

Fig. 3. The degradation of RhB under different reaction conditions (a). Concentration: [RhB] = 10 mg L⁻¹, [PMS] = 0.4 g L⁻¹, [catalyst] = 0.2 g L⁻¹, volume: 20 mL; temperature: 25 °C; initial solution pH: 7.0; pseudo-first order kinetics of different materials (b).

Fig. 4. The influence of catalyst (a) and PMS (b) dosage, initial pH (c) in RhB removal and the efficiencies of different oxidants in Fe₃O₄@MIL-101(Fe, Co)/PMS system (d). Concentration: [dyes] = 10 mg L⁻¹ (for a–d), [PMS] = 0.4 g L⁻¹ (for a, c, d), [catalyst] = 0.2 g L⁻¹ (for b–d), volume: 20 mL; temperature: 25; initial solution pH: 7.0.

Fig. 5. Effects of chloride (a) and bicarbonate (b) on RhB degradation in Fe₃O₄@MIL-101(Fe, Co)/PMS system. Concentration: [RhB] = 10 mg L⁻¹, [PMS] = 0.4 g L⁻¹, [catalyst] = 0.2 g L⁻¹, volume: 20 mL; temperature: 25 °C; initial solution pH: 7.0.