Search

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]

The nanoscaled zero-valent iron (nZVI) supported zeolite MCM-41 composites (nZVI/MCM) were synthesized, and applied for the immobilization of Cr(VI) from aqueous solutions. The precise role of MCM-41 and nZVI in the immobilization and reduction of Cr(VI) was characterized using SEM, TEM, HRTEM, HRTEM-EDS, XPS and EXAFS techniques. Comparing to the bare nZVI nanoparticles, the as-synthesized nZVI/MCM composites showed higher efficiency on Cr(VI) immobilization due to the high synergistic effect of Cr(VI) reduction by nZVI and sorption by MCM-41. The morphology and visualizing analysis indicated that nZVI was uniformly distributed on the surfaces of MCM-41, which reduced the aggregation of nZVI apparently and thereby increased the reduction activity. XPS and EXAFS analysis showed that nZVI could promote Cr(VI) reduction into Cr(III), and the sorption and reduction reactions were occurred on bare nZVI. MCM-41 acted as a scavenger for the insoluble products, which could improve the reduction activity of nZVI. The high performance of nZVI/MCM composites showed the promising strategy for the efficient decontamination of Cr(VI) pollution in environmental pollution cleanup. [ABSTRACT FROM AUTHOR]

Radioactive uranium removal plays a key role in energy development and environmental security. Sulfide nanoscale zero-valent iron (S-NZVI) has good antioxidant capacity, dispersibility and activity to eliminate U(VI) from wastewater, but the removal efficiency is limited. To improve the reduction and adsorption capacity of S-NZVI, through treating Fe3+ solution by nitro-functionalized UiO-66 (UiO-66-NO 2) with high porosity, UiO-66-NO 2 enhanced S-NZVI adsorbent (S-NZVI/UiO-66) was prepared by liquid phase reduction method. The smaller size and larger specific surface area of S-NZVI/UiO-66 were confirmed by a variety of characterization techniques. Based on the excellent surface structure and reactivity, the U(VI) removal capacity of S-NZVI/UiO-66 (895 mg g−1) was much better than S-NZVI (434 mg g−1) and UiO-66-NO 2 (267 mg g−1). The impacts of pH, background ion strength, coexisting ions and different water environments on adsorption were studied via macroscopic batch experiments. The results showed that S-NZVI/UiO-66 could remove U(VI) adequately in a wide pH range. The removal rate was basically not affected by the concentration of NaNO 3 , demonstrating that the adsorption process of U(VI) on S-NZVI/UiO-66 tended to inner surface complexation. From XPS technique combined with the results of batch adsorption experiments, it was clear that the elimination mechanisms of U(VI) by S-NZVI/UiO-66 were mainly the physical adsorption, electrostatic attraction and complexation of UiO-66-NO 2 , and the reduction and complexation of S-NZVI. Therefore, it is believed that S-NZVI/UiO-66 has a great potential to be an excellent adsorbent in the field of the environment remediation. Moreover, S-NZVI/UiO-66 promises to be a novel nanomaterial for solving the problem of radionuclide contamination in practical environments. [Display omitted] • The pretreatment of UiO-66-NO 2 can effectively reduce the size of S-NZVI. • S-NZVI/UiO had a better specific surface area than the original S-NZVI. • The practical application potential of S-NZVI/UiO was confirmed. • The removal mechanisms were adsorption and reduction. [ABSTRACT FROM AUTHOR]

Toxic metals and organic pollutants have become serious environment issues because these contaminants can cause indelible damage to human health and aquatic organism. Various materials have shown great potential in removing conventional contaminants and purifying water. Among them, carbon nanofibers (CNFs) have been regarded as promising candidates in the purification of water environments, owing to their distinct physical/chemical properties, but the connection between properties of CNFs and their removal performance receives few attentions. In this systematic review, we summarize the recent processes in synthetic strategies of CNFs, and highlight their water environmental applications via multiple interactions (π-π interaction, electrostatic interaction, and surface complexation). Some challenges and future outlooks of CNFs materials are briefly discussed. The content presented here will provide a helpful reference value for promoting the development of CNF-based nanomaterials and comprehend the significance of purifying water environments and protecting nature from pollutants. [Display omitted] • Abundant functional groups of carbon nanofibers promote water purification. • Surface modification and composite materials improve the removal performance. • Metal ions are removed via electrostatic interaction and surface complexation. • Organic contaminants are eliminated by π-π interaction and hydrophobic interaction. [ABSTRACT FROM AUTHOR]

Radioactive pollutants have always been the top priority in wastewater, and searching a green and efficient treatment technology remains a significant challenge. In this study, a novel melamine sponge supported sulfurized nanoscale zero-valent iron (MS@S-NZVI) material with high dispersion was firstly designed to effectively capture U(VI) from water environment. The target material could retain its original structure in water due to the excellent mechanical strength of MS, which greatly inhibited the aggregation of S-NZVI. A series of characterization techniques, such as SEM, XRD, FTIR, TGA and XPS, had proved the effective synthesis and excellent structural properties of the MS@S-NZVI. The faster reaction equilibrium (<1 h) and higher maximum adsorption capacity (180 mg/g at pH = 5 and 298 K) exposed the perfect performance of target material in the elimination of U(VI). In addition, further researches in different water systems exhibited that MS@S-NZVI had a significant U(VI) removal rate in simulated wastewater systems. Finally, the removal process of MS@S-NZVI to U(VI) could be divided into three pathways through the XPS technique, adsorption and reduction were the main reaction mechanisms. This study provides a new insight into the utilization of melamine sponge and a prospect for the practical application of S-NZVI in the removal of radionuclide. [Display omitted] • Melamine sponge was used to support S-NZVI for the first time. • The structure of sponge enabled MS@S-NZVI to disperse fully in water. • The practical application potential of MS@S-NZVI was confirmed. • Adsorption and reduction were the main reaction mechanisms. [ABSTRACT FROM AUTHOR]

In this paper, nanoscale zero-valent iron (NZVI), which has great potential in environmental purification is introduced. However, NZVI is easy to accumulate and oxidize, which limits its ability to remove pollutants. Hence several modified NZVI are proposed to overcome its shortcomings in this paper. The heavy metal ions, radionuclides and organic pollutants in the environment are removal by NZVI based materials, and their removal behaviors had been analyzed. This paper also reviews the factors affecting the removal of pollutants by NZVI-based materials, such as pH, ionic strength, contact time, reaction temperature, interfering ions and humic acids. In addition, it is also introduced that NZVI is toxic in the environment, and it also can be recovered and has different removal effects in different water environment. In short, this paper gives a comprehensive summary of NZVI, including its modification methods, pollutants removal, influencing factors of pollutants removal and implication to environment. It provides a strong theoretical basis for the future development of NZVI based materials. [Display omitted] • The characteristics of NZVI-based materials are briefly introduced and summarized. • The removal mechanisms of different pollutants are highlighted. • The influence factors and environmental implications are analyzed. • Future researches of NZVI-based materials in water remediation are discussed. [ABSTRACT FROM AUTHOR]

Highly porous zeolitic imidazolate frameworks (ZIFs), with disparate metal ions (ZIF-8 and ZIF-67), disparate organic ligands (ZIF-9 and ZIF-67), single or double central metal atoms (ZIF-8, Zn/Co-ZIF and ZIF-67) were prepared and used in the elimination of typical radionuclide U(VI). The detailed interaction mechanisms were studied by batch experiments, spectral analyses and DFT calculation. Langmuir isotherms model revealed a decreasing tendency to remove U(VI): ZIF-8 (540.4 mg/g) > Zn/Co-ZIF (527.5 mg/g) > ZIF-9 (448.6 mg/g) > ZIF-67 (368.2 mg/g). Based on the effects of pH and foreign ions, FTIR and XPS spectra analyses, the possible interaction mechanisms of U(VI) onto ZIFs were surface complexation and electrostatic interaction. Among them, ZIF-8 with Zn metal center and 2-methylimidazolate organic ligand had the best elimination capacity for U(VI) because of its large surface area, active metal ion and abundant nitrogen-containing groups (e.g., C–N, Zn–N and C N). Specially, the adsorption energy of ZIF-8-Zn2-UO 2 2+ structure was −2.299 eV obtained by DFT calculation, illustrating that U(VI) and N atoms were formed the most stable bidentate coordination compounds. This paper highlights the effects of the hydroxylated metals, the functional groups of the imidazole ring on the elimination of U(VI), which can provide constructive suggestions for further adsorbent materials amelioration. Image 1 • ZIF-8, ZIF-9, ZIF-67 and Zn/Co-ZIF were fabricated by stirring at room temperature. • Excellent structural performances endowed four ZIFs outstanding sorption capacity. • The differences in adsorption mechanism of four ZIFs were investigated in detail. • The N atoms of ZIF-8 formed bidentate coordination compounds with U(VI). [ABSTRACT FROM AUTHOR]