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With the advantages of high atomic utilization, clear and uniform active sites, high catalytic activity, outstanding stability, excellent selectivity and recyclability, iron single-atom materials have shown promising application in the fields of electrocatalysis, hydrogen production, batteries, and sensors. However, the research work on the efficient removal of various toxic and hazardous pollutants from aqueous solutions using iron single-atom materials was still limited. Their properties such as environmental compatibility, high specific surface area and functionality have unrivaled natural advantages in degrading pollutants in aqueous solutions, which deserve in-depth exploration by researchers. However, pure single-atom materials were thermodynamically unstable and tended to aggregate into nanoclusters and particles. Therefore, single-atom materials were often loaded onto different support materials, while the activity of materials depended mainly on the physicochemical properties of the support materials and the coordination mode between the single-atoms and the support materials. In this review, the preparation and physicochemical properties of iron single-atom materials supported by commonly used carrier materials (such as g-C 3 N 4 , MOFs, COFs, biochar, etc.) were summarized firstly. The applications of different materials for organic pollutants degradation and heavy metal ions removal in aqueous environment were further analyzed, and influence factors and reaction mechanisms for pollutants treatment were investigated. The main mechanism of organic pollutants degradation was catalytic degradation, while the mechanism of heavy metal ions removal was adsorption and redox. Finally, prospects and personal insights were provided for the utilization of iron single-atom materials in environmental pollution decontamination. [Display omitted] • The preparation and properties of iron single-atom materials are summarized. • The influencing factors of removing environmental pollutants are introduced. • The mechanisms mainly include catalytic degradation, adsorption and redox. • The possible degradation pathways of typical pollutants are predicted. • The opportunities and challenges of iron single-atom materials are presented. [ABSTRACT FROM AUTHOR]

Seawater is rich in uranium resources, but the marine environment is complicated and changeable, as well as the presence of a lot of competing ions. These are disturbing factors that cannot be ignored in seawater uranium extraction. The synthesis of adsorbents with good stability, high selectivity and large adsorption capacity has been the focus of attention. The composite adsorbent MXene-AO@LZU1 was prepared using electrostatic self-assembly of transition metal carbides and nitrides (MXenes) with structurally stable covalent organic frameworks (COF-LZU1). The results of characterizations showed that MXene-AO@LZU1 was rich in functional groups and had an effective improvement in specific surface area. MXene-AO@LZU1 exhibited an efficient performance for [UO 2 (CO 3) 3 ]4- with an adsorption saturation capacity of 88.8 mg·g−1. The adsorption amount in the simulated seawater also reached 6.8 mg·g−1. MXene-AO@LZU1 had a good selectivity for uranium and outstanding stability under various extreme conditions. In addition, XPS showed that the adsorption of uranium by MXene-AO@LZU1 relied mainly on the complexation of oxygen/nitrogen-containing functional groups with [UO 2 (CO 3) 3 ]4-. This study explored the great potential of MXenes and COFs in seawater uranium extraction, indicating that MXene-AO@LZU1 was an efficient and stable adsorbent with good development prospects. This finding was of great importance for the application of composite materials in actual environmental cleanup, and could be extended to efficiently remove other pollutants by rational ligands design. [Display omitted] • MXene-AO@LZU1 composite material was obtained by electrostatic self-assembly method. • The saturation adsorption capacity for [UO 2 (CO 3) 3 ]4- was 88.8 mg·g−1. • The adsorption amount in the simulated seawater also reached 6.8 mg·g−1. • Abundant nitrogen/oxygen functional groups promote uranium removal. • Main removal mechanism included surface complexation. [ABSTRACT FROM AUTHOR]

Both environment and human beings were menaced by the widespread application of radioactive uranium, high-performance and effective elimination of uranium from wastewater is of important meaning for development of environmental sustainability in the future. In this study, the water-stable MOF material and the highly crystalline COF were compounded by a mild hydrothermal strategy, which achieved efficient removal of U(VI) through the synergistic effect. The composites showed the characteristics of both COFs and MOFs, which will possess higher stability, larger surface area and faster adsorption efficiency that cannot be carried out by a single component. Batch experiments and characterizations (SEM, TEM, XRD, FT-IR, BET, XPS, etc.) indicated that UiO-66-NH 2 @LZU1 had more stable and multi-layer pore structure and rich active functional groups. The Langmuir model and the pseudo-second-order kinetics fitting was more suitable for the U(VI) elimination process. The greatest uranium adsorbing capacity of UiO-66-NH 2 @LZU1 (180.4 mg g−1) was observed to exceed the UiO-66-NH 2 (108.8 mg g−1) and COF-LZU1 (65.8 mg g−1), which reached the excellent hybrid effects. Furthermore, FT-IR and XPS analyses confirmed that the most nitrogen-containing group from COF-LZU1 and oxygen-containing group of UiO-66-NH 2 could be combined with U(VI). In addition, electrostatic interaction was also a mechanism during the removal process. This work displayed that UiO-66-NH 2 @LZU1 was a prospective hybrid material for radioactive waste remediation. The compound method and application mentioned in this work had provided a theoretical basis for designing and developing multi-functional composite adsorbents, which contributed to the development of new materials for radioactive wastewater treatment technologies. [Display omitted] • UiO-66-NH 2 @LZU1 composite material was obtained by solvothermal method. • Highly efficient uranium adsorbent, adsorption capacity reached 163.1 mg g−1. • Abundant nitrogen/oxygen functional groups promote uranium removal. • Main removal mechanism included electrostatic interaction and surface complexation. [ABSTRACT FROM AUTHOR]