Recently, reactive iron species (RFeS) have shown great potential for the selective degradation of emerging organic contaminants (EOCs). However, the rapid generation of RFeS for the selective and efficient degradation of EOCs over a wide pH range is still challenging. Herein, we constructed FeN4 structures on a carbon nanotube (CNT) to obtain single-atom catalysts (FeSA-N-CNT) to generate RFeS in the presence of peroxymonosulfate (PMS). The obtained FeSA-N-CNT/PMS system exhibited outstanding and selective reactivity for oxidizing EOCs over a wide pH range (3.0–9.0). Several lines of evidences suggested that RFeS existing as an FeN4O intermediate was the predominant oxidant, while SO4 ·– and HO· were the secondary oxidants. Density functional theory calculation results revealed that a CNT played a key role in optimizing the distribution of bonding and antibonding states in the Fe 3d orbital, resulting in the outstanding ability of FeSA-N-CNT for PMS chemical adsorption and activation. Moreover, CNT could significantly enhance the reactivity of the FeN4O intermediate by increasing the overlap of electrons of the Fe 3d orbital, O 2p orbital, and bisphenol A near the Fermi level. The results of this study can advance the understanding of RFeS generation in a heterogeneous system over a wide pH range and the application of RFeS in real practice.

Iron-containing metal-organic frameworks (MOFs) have gradually emerged as environmentally benign alternatives for reducing the levels of environmental contamination because of their advantages, such as readily obtained raw materials with low cost, nontoxic metal source with good biocompatibility, and distinguished physicochemical features e.g., high porosity, framework flexibility, and semiconductor properties. In this study, we reported an innovative strategy for synthesizing an iron-based MOF, MIL-88B, at room temperature. The novelty of this strategy was the use of ethanol as solvent and the pretreatment of dry milling with neither the bulk use of a toxic organic solvent nor the addition of extremely dangerous hydrofluoric acid or strong alkali. The synthesized MIL-88B(Fe) was evaluated as a sorbent for removing arsenate in water and it exhibited high adsorption capacity (156.7 mg g) at a low dosage. The removal capacity of trace arsenate on MIL-88B(Fe) was 32.3 mg g at a low equilibrium concentration (6.4 μg L), which satisfied the arsenic threshold for drinking water. The results of Fourier transform infrared and X-ray photoelectron spectroscopy indicated that the As(v) molecules bonded with the oxygen molecules, which were coordinated with FeO clusters in the framework. This work presented the potential use of the up-scaled MIL-88B as an excellent sorbent for purifying arsenate-contaminated water.

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