Enhanced catalytic activity of MIL-101(Fe) with coordinatively unsaturated sites for activating persulfate to degrade organic pollutants.

In this work, four novel defective MIL-101(Fe) catalysts with coordinatively unsaturated sites were successfully prepared via a facile synthesis strategy by employing benzoic acid, acetic acid, oxalic acid, or citric acid as a modulator. The modified catalysts were demonstrated the existence of defects in the parent framework by a series of characterizations. As compared to the initial MIL-101(Fe), the electronic structure of defective MIL-101(Fe) catalyst was effectively adjusted; meanwhile, the coordinatively unsaturated Fe sites were efficiently generated and the pore sizes were enlarged. Besides, the defective MIL-101(Fe) catalysts exhibited excellent catalytic performance for rhodamine B degradation by persulfate activation. To be specific, the degradation rates of rhodamine B increased from 58.70 to 94.05%, 86.11%, 78.70%, and 82.62%, respectively. The defective MIL-101(Fe) with coordinatively unsaturated sites showed good reusability and stability, and the probable catalytic mechanism was also investigated.

Quinone-modified metal-organic frameworks MIL-101(Fe) as heterogeneous catalysts of persulfate activation for degradation of aqueous organic pollutants.

In this work, quinone-modified metal-organic framework MIL-101(Fe)(Q-MIL-101(Fe)), as a novel heterogeneous Fenton-like catalyst, was synthesized for the activation of persulfate (PS) to remove bisphenol A (BPA). The synthetic Q-MIL-101(Fe) was characterized via X-ray diffraction, scanning electron microscope, Fourier transform infrared, electrochemical impedance spectroscopy, cyclic voltammetry and X-ray photoelectron spectroscopy. As compared to the pure MIL-101(Fe), Q-MIL-101(Fe) displayed better catalytic activity and reusability. The results manifested that the Q-MIL-101(Fe) kept quinone units, which successfully promoted the redox cycling of Fe3+/Fe2+ and enhanced the removal efficiency. In addition, the reaction factors of Q-MIL-101(Fe) were studied (e.g. pH, catalyst dosage, PS concentration and temperature), showing that the optimum conditions were [catalyst] = 0.2 g/L, [BPA] = 60 mg/L, [PS] = 4 mmol/L, pH = 6.79, temperature = 25 °C. On the basis of these findings, the probable mechanism on the heterogeneous activation of PS by Q-MIL-101(Fe) was proposed.

Microfluidic Fabrication of Bubble-Propelled Micromotors for Wastewater Treatment.

Bubble-propelled micromotors with controllable shapes and sizes have been developed by a microfluidic method, which serves for effective wastewater treatment. Using the emulsion from microfluidics as the template, monodisperse micromotors can be fabricated in large quantities based on phase separation and UV-induced monomer polymerization. By adjusting the volume ratio of the two immiscible oils (ethoxylated trimethylolpropane triacrylate/paraffin oil) in the initial emulsion, the geometry of the resulting micromotor can be precisely controlled from nearly spherical, hemispherical to crescent-shaped. The size of the micromotor can be manipulated by varying the fluid flow parameters. In addition, by incorporating functional nanoparticles into the asymmetric structure, the micromotor can be functionalized flexibly for water remediation. In this research, Fe3O4 and MnO2 nanoparticles were successfully loaded on Janus micromotors. Fe3O4 nanoparticles can act as catalysts for pollutant degradation and also control the movement direction of micromotors. MnO2 nanoparticles on the concave of the micromotor catalyzed H2O2 to produce bubble propulsion motion in solution, which further enhanced the degradation of pollutants. Consequently, the obtained micromotor demonstrated effective degradation of methylene blue and can be easily recovered by magnets. Furthermore, this simple and flexible strategy offers a synthetic way for anisotropic Janus particles, which will broaden their potential application.