A comparison of the dechlorination mechanisms and Ni release styles of chloroalkane and chloroalkene removal using nickel/iron nanoparticles

Recent advances in bimetallic nanoscale zero-valent iron composite for water decontamination: Synthesis, modification and mechanisms

The environmental pollution of water is one of the problems that have plagued human society. The bimetallic nanoscale zero-valent iron (BnZVI) technology has increased wide attention owing to its high performance for water treatment and soil remediation. In recent years, the BnZVI technology based on the development of nZVI has been further developed. The material chemistry, synthesis methods, and immobilization or surface stabilization of bimetals are discussed. Further, the data of BnZVI (Fe/Ni, Fe/Cu, Fe/Pd) articles that have been studied more frequently in the last decade are summarized in terms of the types of contaminants and the number of research literatures on the same contaminants. Five contaminants including trichloroethylene (TCE), Decabromodi-phenyl Ether (BDE209), chromium (Cr(VI)), nitrate and 2,4-dichlorophenol (2,4-DCP) were selected for in-depth discussion on their influencing factors and removal or degradation mechanisms. Herein, comprehensive views towards mechanisms of BnZVI applications including adsorption, hydrodehalogenation and reduction are provided. Particularly, some ambiguous concepts about formation of micro progenitor cell, production of hydrogen radicals (H·) and H2 and the electron transfer are highlighted. Besides, in-depth discussion of selectivity for N2 from nitrates and co-precipitation of chromium are emphasized. The difference of BnZVI is also discussed.

Assessment of green tea reductive degradation of halogenated solvents

Green tea (GT) leaves can be brewed into a solution rich in polyphenols that serve as effective reducing agents, and the complexes formed by combining green tea with ferrous ion (GT/Fe(II)) can provide an elevated reduction potential. The dissociated GT polyphenols at alkaline pH can dramatically increase the formation of GT/Fe(II) complexes. This experimental work evaluated the reductive reactivity of alkaline GT solution and GT/Fe(II) complexes (at pH 10) on 14 halogenated volatile organic compounds (VOCs). Carbon tetrachloride (CT), with a highest carbon oxidation state (COS) of IV, was observed to be degradable by the alkaline GT solution, while all others proved ineffective. The GT/Fe(II) complexes are very reactive and capable of degrading halogenated methanes, ethanes, and ethenes, in which chemical structures exhibit zero or positive COS values, and the chlorine or bromine atom is bonded at the saturated carbon atom, such as CT, chloroform, bromoform, dibromomethane, 1,1,1-trichloroethane, and 1,1,1,2-tetrachloroethane. The linear free energy relationship (LFER) approach was used to determine the overall reduction potentials (E_H⁰) of the alkaline GT solution and GT/Fe(II) complexes, which were found to be -0.131 V and -0.368 V, respectively. These findings demonstrated that GT/Fe(II) complexes exhibit the potential to remediate halogenated contaminants and the E_H⁰ information obtained in this study may serve as a reference in determining probable reactivity that contributes to degradation of environmental contaminants.

Biotechnology and nanotechnology for remediation of chlorinated volatile organic compounds: current perspectives

Chlorinated volatile organic compounds (CVOCs) are persistent organic pollutants which are harmful to public health and the environment. Many CVOCs occur in substantial quantities in groundwater and soil, even though their use has been more carefully managed and restricted in recent years. This review summarizes recent data on several innovative treatment solutions for CVOC-affected media including bioremediation, phytoremediation, nanoscale zero-valent iron (nZVI)-based reductive dehalogenation, and photooxidation. There is no optimally developed single technology; therefore, the possibility of using combined technologies for CVOC remediation, for example bioremediation integrated with reduction by nZVI, is presented. Some methods are still in the development stage. Advantages and disadvantages of each treatment strategy are provided. It is hoped that this paper can provide a basic framework for selection of successful CVOC remediation strategies.

The removal of chlorinated aliphatic hydrocarbons from water using reactive activated carbon: the influence of synthesis factors and reaction environments

Granular activated carbon (GAC) composite incorporated with nanoscale zerovalent iron (nZVI) particles (reactive activated carbon, RAC) was synthesized by the liquid phase precipitation method and used to remove chlorinated aliphatic hydrocarbons (CAHs) from water. The influence of synthesis factors, such as base carbon types and annealing treatment temperature, and environmental factors, such as the molecular structure of CAHs, common ionic species and natural organic matter, on the removal capacities of RAC for CAHs was investigated. Mesoporous carbon with high hardness is a good candidate for base carbon, and high annealing treatment (up to 700°C) enhanced the total removal capacity of RAC for CAHs. The removal capacities of RAC for CAHs are consistent with the following order: tetrachloroethene >1,1,1-trichloroethane > trichloroethylene, and the CAH removal processes fit the pseudo-first-order reaction kinetics model well. The removal mechanism of CAHs might be in accordance with a sequence of adsorption, diffusion and dechlorination in two heterogeneous GAC and nZVI materials. The presence of other CAHs, common ionic species and humic acid all inhibited the removal of CAHs. The removal ability of aged RAC for CAHs decreased slightly compared with that of fresh RAC, which demonstrated its good application potential in underground water remediation.