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The dechlorination of 2,4-dichlorophenol (2,4-DCP) by Ni-Fe nanoparticles in the presence of humic acid (HA) was investigated to understand the feasibility of using Ni-Fe for the in situ remediation of contaminated groundwater. 2,4-DCP was first adsorbed by Ni-Fe nanoparticles, then quickly reduced to o-chlorophenol (o-CP), p-chlorophenol (p-CP), and finally to phenol (P). However, the introduction of HA decreased the removal percentage of 2,4-DCP, as a result, the phenol production rates dropped from 86% (in the absence of HA) to 29% within 2h. Our data suggested that the dechlorination rate was dependent on a number of factors including Ni-Fe availability, Ni loading percentage over Fe, temperature, pH, and HA concentration. In particular, the removal percentage of 2,4-DCP was determined to be 100, 99, 95, 84 and 69%, for HA concentrations of 0, 5, 10, 30 and 40 mg L(-1), respectively. The kinetic calculations for the dechlorination of 2,4-DCP indicated that k values for 2,4-DCP dechlorination dropped from 0.14, 0.051, 0.039, 0.021 to 0.011 min(-1) with increasing concentrations of HA from 0, 5, 10, 30 to 40 mg L(-1).

Abstract: This paper describes the synthesis of sodium carboxymethyl cellulose (CMC)-stabilized Pd/Fe nanoparticles and their applications to the dechlorination of 2,4-dichlorophenoxyacetic acid (2,4-D) under controlled laboratorial conditions. For this purpose batch mode experiments were conducted to understand the effects of CMC on the surface characteristics of Pd/Fe nanoparticles, optimum removal of 2,4-D and other surface interactions mechanism. Our experimental results demonstrated considerable enhancements in particle stability and chemical reactivity with the addition of CMC to Pd/Fe nanoparticles. Transmission electron microscopy (TEM) analysis indicated that CMC-stabilized Pd/Fe nanoparticles were well dispersed, and nanoparticles remained in suspension for days compared to non-stabilized Pd/Fe nanoparticles precipitated within minutes. The isoelectric point (IEP) of the nanoparticles shifted from pH 6.5 to 2.5, suggesting that CMC-stabilized Pd/Fe nanoparticles were negatively charged over a wider pH range. Our batch experiments demonstrated that CMC-stabilized Pd/Fe nanoparticles (0.6gFeL−1) were able to remove much higher levels of 2,4-D with only one intermediate 2-chlorophenoxyacetic acid (2-CPA) and the final organic product phenoxyacetic acid (PA), than non-stabilized Pd/Fe nanoparticles or microsized Pd/Fe particles. The removal percentage of 2,4-D increased from 10% to nearly 100% as the reaction pH decreased from 11.5 to 2.5. The optimal CMC/Fe mass ratio for the dechlorination of 2,4-D was determined to be 5/1, and the removal of 2,4-D was evidently hindered by an overdose of CMC. [Copyright &y& Elsevier]

Abstract: The photocatalytic degradation of 2-chlorophenol (2-CP) irradiated with visible light over iodine doped TiO2 (IT) modified with SnO2 (SIT) nanoparticles has been investigated in this study. The structure and optical properties of the SIT catalysts have been well characterized by X-ray diffraction, the Brunauer–Emmett–Teller method, transmission electron microscopy, UV–visible absorption spectra and X-ray photoelectron spectroscopy. The effects of preparation conditions, such as SnO2 content and calcination temperature, on the photocatalytic degradation efficiency have been surveyed in detail. The improved photocatalytic activity of SIT is derived from the synergistic effect between the SnO2 and IT, which promoted the efficiency of migration of the photogenerated carriers at the interface of the catalysts and thereby enhanced the efficiency of photon harvesting in the visible region. The action of scavengers (fluoride ion, iodide ion, tert-butyl alcohol, and persulfate ion), as well as N2 purging on the photodegradation rate reveal that the valence band hole is mainly responsible for the effective photocatalytic removal of 2-CP and the corresponding TOC reduction. [Copyright &y& Elsevier]

Abstract: Pd/Fe bimetallic nanoparticles were synthesized for treatment of 2,4-dichlorophenol (2,4-DCP) in the presence of humic acid (HA), in order to understand their applicability for in situ remediation of groundwater. In this case, 2,4-DCP was catalytically dechlorinated to form the final products – phenol (P) via two intermediates, namely o-chlorophenol (o-CP) and p-chlorophenol (p-CP). We demonstrated that the carbon mass balances during the dechlorination were in the range of 82–91%, and other carbons were absorbed on the surface of Pd/Fe bimetallic nanoparticles. Our results suggest the dechlorination reaction of 2,4-DCP by Pd/Fe bimetallic nanoparticles in the presence of HA followed pseudo-first-order kinetics. HA competed for reaction sites on the Pd/Fe bimetallic nanoparticles with 2,4-DCP, and thus reduced the efficiency and rate of the dechlorination of 2,4-DCP. Efficiencies of dechlorination and phenol formations increased significantly as the Pd content increased from 0.10wt.%, 0.15wt.% to 0.20wt.%, the removal percentage of 2,4-DCP increased from 70.4%, 98.4% to 99.4% within 300min, respectively, the nitrate (NO3 −) content in water also has a significant impact on 2,4-DCP dechlorination efficiency. Our results show that no other intermediates were generated besides Cl−, o-CP, p-CP and phenol during the catalytic dechlorination of 2,4-DCP. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes the use of highly reactive magnetite (Fe3O4) nanoparticles-stabilized Fe0 nanocomposites for the reduction and mitigation of hexavalent chromium Cr(VI) species in aqueous solutions. Higher proportions of Fe3O4 in the nanocomposites could increase the rate of Cr(VI) reduction. In the absence of magnetite, the Cr(VI) mitigation rate was just 51.4% after 60min of reaction, while with an initial Fe3O4 mass loading of 3gl−1, the Cr(VI) mitigation rate was nearly 100% after 60min. The optimal ratio of Fe3O4:Fe0 for the mitigation of Cr(VI) was found to be 40:1. Otherwise, solution pHs significantly affected the rate of Cr(VI) reduction, with reactions occurring more rapidly under acidic or neutral than basic conditions. It is hypothesized that the high efficiency of the Fe3O4 nanoparticles-stabilized Fe0 nanocomposites for Cr(VI) reduction was a direct result of the attachment of Fe0 nanoparticles to the surface of magnetite, which prevents the aggregation of nano-Fe0, moreover, the electron transfer during the reduction process most likely takes place via Fe0 nanoparticles that are located at the magnetite octahedral sites, which are versatile redox centers as they can accommodate both Fe(III) and Fe(II), and this will promote the reduction of Cr(VI). Cr(VI) reduction is coupled with nano-Fe0 oxidation. Nano-Fe0 particles are located at the magnetite octahedral sites. Ions of Fe(II) and Fe(III) accommodated by magnetite octahedral sites are products of nano-Fe0 oxidation. Therefore, Cr(VI) reduction is mediated either by nano-Fe0 (direct reduction) or Fe(II) species (indirect reduction). Additionally, catalytic Cr(VI) reduction by molecular H2 (or atomic H) is possible. [Copyright &y& Elsevier]