Removal of organic compounds by nanoscale zero-valent iron and its composites

Recent industrial and urban activities have led to elevated concentrations of a wide range of contaminants in groundwater and wastewater, which affect the health of millions of people worldwide. In recent years, the use of zero-valent iron (ZVI) for the treatment of toxic contaminants in groundwater and wastewater has received wide attention and encouraging treatment efficiencies have been documented. This paper gives an overview of the recent advances of ZVI and progress obtained during the groundwater remediation and wastewater treatment utilizing ZVI (including nanoscale zero-valent iron (nZVI)) for the removal of: (a) chlorinated organic compounds, (b) nitroaromatic compounds, (c) arsenic, (d) heavy metals, (e) nitrate, (f) dyes, and (g) phenol. Reaction mechanisms and removal efficiencies were studied and evaluated. It was found that ZVI materials with wide availability have appreciable removal efficiency for several types of contaminants. Concerning ZVI for future research, some suggestions are proposed and conclusions have been drawn. Copyright © 2014 Elsevier B.V. All rights reserved.

Summary Covalent organic frameworks (COFs) are a new type of crystalline porous polymers known for chemical stability, excellent structural regularity, robust framework, and inherent porosity, making them promising materials for capturing various types of pollutants from aqueous solutions. This review thoroughly presents the recent progress and advances of COFs and COF-based materials as superior adsorbents for the efficient removal of toxic heavy metal ions, radionuclides, and organic pollutants. Information about the interaction mechanisms between various pollutants and COF-based materials are summarized from the macroscopic and microscopic standpoints, including batch experiments, theoretical calculations, and advanced spectroscopy analysis. The adsorption properties of various COF-based materials are assessed and compared with other widely used adsorbents. Several commonly used strategies to enhance COF-based materials’ adsorption performance and the relationship between structural property and sorption ability are also discussed. Finally, a summary and perspective on the opportunities and challenges of COFs and COF-based materials are proposed to provide some inspiring information on designing and fabricating COFs and COF-based materials for environmental pollution management.

Most nonenzymatic antioxidant activity (scavenging of free radicals, inhibition of lipid peroxidation, etc.) is mediated by redox reactions. The antioxidant (AO) activity of polyphenols (PPs), as ferric-reducing power, was determined for the first time using a modified FRAP (ferric reducing/antioxidant power) assay. Reaction was followed for 30 min, and both Fe(II) standards and samples were dissolved in the same solvent to allow comparison. Selected representative PPs included flavonoids (quercetin, rutin, and catechin), resveratrol, tannic acid, and phenolic acids (gallic, caffeic, and ferulic). Carotenoids (beta-carotene and zeaxanthine), ascorbic acid, Trolox, and BHA were included for comparison. Equivalent concentration 1 (EC(1)), as the concentration of AO with a reducing effect equivalent to 1 mmol/L Fe(II), was used to compare AO efficiency. PPs had lower EC(1) values, and therefore higher reducing power, than ascorbic acid and Trolox. Tannic acid and quercetin had the highest AO capacity followed by gallic and caffeic acids. Resveratrol showed the lowest reducing effect. Carotenoids had no ferric reducing ability. Polyphenol's AO efficiency seemed to depend on the extent of hydroxylation and conjugation.