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Mechanochemical (MC) remediation with zero-valent iron (ZVI) as co-milling agent enables the non-combustion and solvent-free disposal of solid halogenated organic pollutants (HOPs) via solid-phase reaction, but suffers from incomplete dechlorination (especially for less chlorinated chemicals). Herein, a reduction-oxidation coupling strategy using ZVI and peroxydisulfate as synergistic (ZVI-PDS) co-milling agents was investigated, with 2,4-dichlorophenol (2,4-DCP) as probe contaminant. By revisiting the MC destruction process of 2,4-DCP by ZVI, the contribution of both reductive and oxidative routes is confirmed, and the inefficient •OH generation is addressed. With ball-to-material and reagent-to-pollutant mass ratios of 30:1 and 13:1, respectively, ZVI-PDS achieves higher dechlorination ratio (86.8%) for 2,4-DCP within 5 h, outcompeting sole ZVI (40.3%) or PDS (33.9%), due to the accumulation of numerous SO 4 •−. As suggested by a two-compartment kinetic model, the optimal ZVI/PDS molar ratio of 4:1 is determined, which balances the relative contribution of reductive/oxidative routes and leads to a maximum mineralization efficiency of 77.4%. The analysis on product distribution verifies the generation of dechlorinated, ring-opening and minor coupling products (with low acute toxicity). This work validates the necessity to couple reduction with oxidation in MC destruction for solid HOPs, and may provide information on reagent formulation. [Display omitted] • A reduction-oxidation strategy is developed for mechanochemical remediation. • Peroxydisulfate enhances the dechlorination ratio of 2,4-dichlorophenol by sole ZVI. • The ZVI/PDS molar ratio controls the relative contribution of reduction/oxidation. • ZVI/PDS favors the mineralization of most 2,4-DCP with low-toxic residual products. [ABSTRACT FROM AUTHOR]

The catalytic dechlorination of2,4-dichlorophenol (2,4-DCP) by Ni/Fe bimetallic nanoparticles in the presence of humic acid (HA) was investigated in order to understand their applicability forin situremediation of groundwater.2,4-DCP was catalytically dechlorinated to form the final products – phenol (P) via two intermediates,o-chlorophenol (o-CP) andp-chlorophenol (p-CP). It was demonstrated that the carbon mass balances during the dechlorination were between 84% and 92%, and other carbons were adsorbed on the surface of Ni/Fe bimetallic nanoparticles. The experimental results suggest that HA competed for reaction sites on the Ni/Fe bimetallic nanoparticles with2,4-DCP, and thus reduced the efficiency and rate of the dechlorination of2,4-DCP. The catalytic degradation slowed down as the increase of HA in solution, and when HA's concentrations were 0, 10, 20 and 30 mg L−1, the maximum concentrations ofo-CP were 0.025, 0.041, 0.039 and 0.034 mM in 10, 30, 30 and 30 min, respectively. High Ni content, low initial pH value, high Ni/Fe nanoparticles’ dosage and high temperature favoured the catalytic dechlorination of2,4-DCP. The experimental results show that no other intermediates were generated besides Cl−,o-CP,p-CP and P during the catalytic dechlorination of2,4-DCP. [ABSTRACT FROM PUBLISHER]

Abstract: Nanoscale Pd/Fe particles were combined with multi-walled carbon nanotubes (MWNTs) to prepare supported particles (MWNT-stabilized Pd/Fe), which were used to remove 2,4-dichlorophenol (2,4-DCP). The adsorption capacity of MWNTs was found to be increased with the increasing amount of chlorine atoms, and the removal rates of phenol (P), 2-chlorophenol (2-CP), 4-chlorophenol (4-CP) and 2,4-DCP reached 19.7%, 60.5%, 72.0% and 95.1% respectively, in 1min by MWNTs due to π–π interaction. The adsorption kinetics and adsorption isotherm were also discussed. MWNTs as a supporter, was effective for avoiding the agglomeration of nZVI. Furthermore, the speedy removal efficiency of the initial substances (2,4-DCP) reached about 50% in 1min, and over the time continued to rise to 100%, remaining low concentrations (<1mgL−1) of the intermediate substances (o-CP, p-CP), and gradual release of the final substance (P) from MWNT-stabilized Pd/Fe composites during the whole process, proposed a novel method for in situ remediation technology. [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]

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 40mgL−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 0.011min−1 with increasing concentrations of HA from 0, 5, 10, 30 to 40mgL−1. [Copyright &y& Elsevier]