Abstract
Here, we show that NH2-MIL-88B(Fe) can be used as a peroxidase-like catalyst for Fenton-like degradation of methylene blue (MB) in water. The iron-based NH2-MIL-88B(Fe) metal organic framework (MOF) was synthesized by a facile and rapid microwave heating method. It was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, powder X-ray diffraction, and the Brunauer–Emmett–Teller method. The NH2-MIL-88B(Fe) MOF possesses intrinsic oxidase-like and peroxidase-like activities. The reaction parameters that affect MB degradation were investigated, including the solution pH, NH2-MIL-88B(Fe) MOF and H2O2 concentrations, and temperature. The results show that the NH2-MIL-88B(Fe) MOF exhibits a wide working pH range (pH 3.0–11.0), temperature tolerance, and good recyclability for MB removal. Under the optimal conditions, complete removal of MB was achieved within 45 min. In addition, removal of MB was above 80% after five cycles, showing the good recyclability of NH2-MIL-88B(Fe). The NH2-MIL-88B(Fe) MOF has the features of easy preparation, high efficiency, and good recyclability for MB removal in a wide pH range. Electron spin resonance and fluorescence probe results suggest the involvement of hydroxyl radicals in MB degradation. These findings provide new insight into the application of high-efficient MOF-based Fenton-like catalysts for water purification.
Highlights
Metal organic frameworks (MOFs) are composed of metal ions with organic linkers
The catalytic mechanism of NH2-MIL-88B(Fe) was investigated and a possible mechanism is proposed based on electron spin resonance (ESR) and fluorescence probe results for detection of ∙OH free radicals, which confirms the major role of ∙OH free radicals in degradation of methylene blue (MB)
The crystal structure of the as-prepared material was confirmed to be NH2-MIL-88B(Fe) by powder X-ray diffraction (PXRD) (Fig. 1a), which is in agreement with a previous report[29] and indicates the success of NH2-MIL-88B (Fe) synthesis
Summary
The above observation confirms that about half of the MB removal is attributed to NH2-MIL-88B(Fe) acting as a strong peroxidase mimic in aqueous media This is probably because degradation of MB by H2O2 in the presence of NH2-MIL-88B(Fe) mainly originates from generation of highly active ∙OH free radicals. The degradation efficiency of MB and TOC removal are plotted against time at different temperatures in Figs 4d and S5 (Supporting Information). The obvious decrease in the BET surface area suggests the collapse of NH2-MIL-88B(Fe) framework, leading to partial loss of crystallinity and cracks of the NH2-MIL88B(Fe) (Figs S9 and S10, Supporting Information) This contributes to the loss of catalytic activities of NH2-MIL-88B(Fe) after cycles. No additional chemicals are needed to regenerate NH2-MIL-88B(Fe), indicating that this MOF is a promising catalyst with potential applications in water purification
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