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Abstract: The aqueous phase oxidation of gaseous elemental mercury (Hg0) by potassium persulfate (K2S2O8, KPS) catalyzed by Ag+ and Cu2+ was investigated using a glass bubble column reactor. Concentrations of gaseous Hg0 and aqueous Hg2+ were measured by cold vapor generation atomic absorption spectrometry (CVAAS). The effects of several experimental parameters on the oxidation were studied; these include different types of catalysts, pHs and concentrations of potassium persulfate, temperatures, Hg0 inlet concentrations and tertiary butanol (TBA). The results showed that the removal efficiency of Hg0 increased with increasing concentration of potassium persulfate and catalysts Ag+, Cu2+ and Ag+ provided better catalytic effect than Cu2+. For example, in the presence of 5.0mmoll−1 KPS, the mercury removal efficiency could reach 75.4 and 97.0% for an Ag+ concentration of 0.1 and 0.3mmoll−1, respectively, and 69.8 and 81.9% for 0.1 and 0.3mmoll−1 Cu2+. On the other hand, high temperature and the introduction of TBA negatively affect the oxidation. Furthermore, the removal efficiency of Hg0 was much greater in neutral solution than in either acidic or alkaline solution. But the influence of pH was almost eliminated upon the addition of Ag+ and Cu2+, and high Hg0 inlet concentration also has positive impact on the removal efficiency of Hg0. The possible catalytic oxidation mechanism of gaseous mercury by KPS was also proposed. [Copyright &y& Elsevier]

Abstract: Catalysis dechlorination of chlorinated organic matter by palladium/iron bimetallic particles represents one of the latest innovative technologies for contaminated soil and groundwater remediation. The reaction of dechlorination is believed to take place on the surface site of the catalyst in a pseudo-first-order mode. The dechlorination rate increases with an increase of the bulk loading of palladium due to the increase of both the surface loading of palladium and the total surface area exposed. The results show that no other intermediates were generated besides Cl−, benzene and chlorobenzene during dechlorination of o-dichlorobenzene. [Copyright &y& Elsevier]

Abstract: The bioremediation was employed to treat perchlorate-contaminated water. All enrichments and growth of mixed cultures were performed in anaerobic acetate medium. Enrichment cultures were started with activated sludge obtained from a local wastewater treatment plant where it predominantly treats domestic wastewater. Several parameters affecting perchlorate removal were examined through batch experiments, these include the amount of domesticated sludge, the acetate concentration, pH, the C/N ratio and the reaction temperature. The results indicated that acetate was an effective carbon source and electron donor. Under the selected conditions, namely 1.0g domesticated sludge, an acetate concentration of 1.2gl−1, pH 8.0, a C/N ratio of 20 at 40°C, 50mgl−1 perchlorate could be rapidly reduced to non-detectable levels within 24h. [Copyright &y& Elsevier]

Graphical abstract Highlights • TiC doped palladium/nickel foam cathode was synthesized via electroless deposition. • Pd/TiC/Ni foam show superior activity for 2,4-DCBA dechlorination to Pd/Ni foam. • Optimized conditions on 2,4-DCBA dechlorination were investigated. • Possible promotion mechanism by doped TiC over Pd/Ni foam cathode was proposed. Abstract Titanium carbide (TiC) with excellent electrical conductivity, chemical and thermal stabilities has been recognized as one of the most promising electrocatalysts. A novel cathode, titanium carbide doped palladium/nickel foam (TiC-Pd/Ni foam), was synthesized via electroless deposition to improve the performance of Pd/Ni foam in electrocatlytic hydrodechlorination (ECH). TiC can be co-precipitated onto the surface of cathode during galvanic replacement reaction between Pd(II) solution and Ni foam. Both constant potential and constant current tests proved that TiC-Pd/Ni foam cathode performed remarkably higher activity for 2,4-dichlorobenzoic acid (2,4-DCBA) than Pd/Ni foam cathode, owing to the excellent conductivity of TiC and enhanced water dissociation over TiC-Pd/Ni foam cathode. Under the optimized reaction conditions of –0.85 V (vs Ag/AgCl), electrolyte of 10 mM and initial pH of 4, 99.8% of aqueous 2,4-DCBA (0.2 mM) was removed within 90 min. The removal process of the aqueous 2,4-DCBA obeyed first-order decay kinetic model. Over 86.3% of 2,4-DCBA can still be removed by TiC-Pd/Ni foam cathode in the fifth consecutive run within 120 min, which was much higher than that of Pd/Ni foam cathode (37.5%). Consequently, TiC-Pd/Ni foam cathode was a promising design for enhanced ECH activity and reduced operation cost. [ABSTRACT FROM AUTHOR]

Polychlorinated dibenzo- p -dioxins (PCDDs), as a group of notorious anthropogenic environmental toxicants, are arguably ubiquitous in nature. In this study, we investigated the photocatalytic reductive dechlorination of 2-chlorodibenzo- p -dioxin (2-CDD) over Pd/g-C 3 N 4 catalysts under UV–vis irradiation. The g-C 3 N 4 and a series of Pd/g-C 3 N 4 catalysts were prepared by thermal polymerization and mechanical mixing-illumination method and characterized by XRD, TEM, BET, SEM and UV–vis DRS analyses. Among all the samples, the Pd/g-C 3 N 4 (5 wt%) yielded the optimal dechlorination activity with a total 2-CDD conversion of 54% within 4 h, and 76% of those converted 2-CDD were evolved to dibenzo- p -dioxin (DD). The kinetics of dechlorination could be described as pseudo-first-order decay model (R 2  > 0.84). Corresponding rate constants (k) increased from 0.052 to 0.17 h −1 with Pd contents up to 5 wt% and decreased to 0.13 h −1 with a 10 wt% of Pd. The enhanced activities originated from the surface plasmonic resonance (SPR) effect of Pd nanoparticles and the formation of Schottky barrier between Pd and g-C 3 N 4 , which extend the spectrum responsive range and suppress the charge recombination of g-C 3 N 4 . This is the first report on the photocatalytic reductive removal of PCDDs and may provide a new approach for PCDDs pollution control. [ABSTRACT FROM AUTHOR]

Magnetic multi-walled carbon nanotubes (MWCNTs) were prepared to support Pd/Fe nanoparticles, inhibit the aggregation and passivation, and achieve magnetic separation to avoid the environmental risk of nanoparticles. Rapid adsorption of initial contaminant, steady dechlorination, and gradual desorption of final product was observed. The micromorphology, chemical structure, and components of the nanohybrids were comprehensively characterized by a series of analysis technologies, such as EDX, XRD, SEM, TEM, and XPS. The interactions between the nanohybrids compositions were discussed according to the characterization and experimental data. The whole insight of 2,4-dichlorophenol (2,4-DCP) adsorption- dechlorination-desorption was studied in detail, including the pathways, influence factors, dechlorination kinetics and selectivity. Weak acidity (pH = 5.0 and 6.5) favored the 2,4-DCP removal. Satisfactory reactivity of the Pd/Fe-Fe 3 O 4 @MWCNTs nanohybrids was observed in five consecutive runs, and 99.2%, 89.6%, 92.1%, 99.8%, and 99.9% of 2,4-DCP was removed, respectively. Most of the final product (phenol) was steadily desorbed to the liquid phase, resulted in the re-exposure of active sites on the nanohybrids and maintained a longer activity. [ABSTRACT FROM AUTHOR]

In this study, a novel composite adsorbent (HBC–Fe 3 O 4 –MnO 2 ) was synthesized by combining honeycomb briquette cinders (HBC) with Fe 3 O 4 and MnO 2 through a co-precipitation process. The purpose was to make the best use of the oxidative property of MnO 2 and the adsorptive ability of magnetic Fe 3 O 4 for enhanced As(III) and As(V) removal from aqueous solutions. Experimental results showed that the adsorption capacity of As(III) was observed to be much higher than As(V). The maximum adsorption capacity (2.16 mg/g) was achieved for As(III) by using HBC–Fe 3 O 4 –MnO 2 (3:2) as compared to HBC–Fe 3 O 4 –MnO 2 (2:1) and HBC–Fe 3 O 4 –MnO 2 (1:1). The experimental data of As(V) adsorption fitted well with the Langmuir isotherm model, whereas As(III) data was described perfectly by Freundlich model. The pseudo-second-order kinetic model was fitted well for the entire adsorption process of As(III) and As(V) suggesting that the adsorption is a rate-controlling step. Aqueous solution pH was found to greatly affect the adsorption behavior. Furthermore, co-ions including HCO 3 − and PO 4 3− exhibited greater influence on arsenic removal efficiency, whereas Cl − , NO 3 − , SO 4 2− were found to have negligible effects on arsenic removal. Five consecutive adsorption-regeneration cycles confirmed that the adsorbent could be reusable for successive arsenic treatment and can be used in real treatment applications. [ABSTRACT FROM AUTHOR]

Highlights: [•] Fe0-Fe3O4 nanocomposites are embedded in polyvinyl alcohol/sodium alginate beads;. [•] Acidification and reduction after bead molding greatly improve beads performance;. [•] High stability, Cr(VI) removal efficiency and reusability of these beads;. [•] Easy and complete separation after reaction. [Copyright &y& Elsevier]

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: Several heavy metals, including Cu2+, Ni2+, Pb2+, and Zn2+, were investigated in simulated desulfurization solutions to evaluate their interferences with Hg2+ during the reaction with dithiocarbamate type chelating resin (DTCR). Appropriate DTCR dosage and the effect of pH were also explored with respect to restoration of high Hg2+ precipitation efficiency and reduction of mercury concentrations. The experimental results suggested that increasing heavy metal concentration inhibited Hg2+ precipitation efficiency to a considerable extent and the inhibition order of the four heavy metals was Cu2+ >Ni2+ >Pb2+ >Zn2+. However, the coordination ability was closely related to the configuration and the orbital hybridization of each metal. In the cases of Cu2+ and Pb2+, increased DTCR dosage was beneficial to Hg2+ precipitation, which could lay the foundation of practical applications of DTCR dosage for industrial wastewater treatment. The enhanced Hg2+ precipitation performance seen for increasing pH might have come from the deprotonation of sulfur atoms on the DTCR functional groups and the formation of metal hydroxides (M(OH)2, M=Cu, Pb, Hg). [Copyright &y& Elsevier]

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: Mercury (II) (Hg2+) ion can be reduced by aqueous S(IV) (sulfite and/or bisulfite) species, which leads to elemental mercury (Hg0) emissions in wet flue gas desulfurization (FGD) systems. Numerous reports have demonstrated the high trapping efficiency of sodium dithiocarbamate over heavy metals. In this paper, a novel sodium dithiocarbamate, DTCR, was utilized as a precipitator to control Hg2+ reduction and Hg0 emission against S(IV) in FGD solutions. Results indicated that Hg2+ reduction efficiency decreased dramatically while precipitation rate peaked at around 91.0% in consistence with the increment of DTCR dosage. Initial pH and temperature had great inhibitory effects on Hg2+ reduction: the Hg2+ removal rate gradually increased and reached a plateau along with the increment of temperature and initial pH value. Chloride played a key role in Hg2+ reduction and precipitation reactions. When Cl− concentration increased from 0 to 150mM, Hg2+ removal rate dropped from 93.84% to 86.05%, and the Hg2+ reduction rate remained at a low level (<7.8%). SO4 2−, NO3 − and other common metal ions would affect the efficiency of Hg2+ reduction and precipitation reactions in the simulated desulfurization solutions: Hg2+ removal rate could always be above 90%, while Hg2+ reduction rate was maintained at below 10%. The predominance of DTCR over aqueous S(IV), indicated by the results above, has wide industrial applications in FGD systems. [Copyright &y& Elsevier]

Abstract: The widely existing fly ash and soot produced during the process of combustion, which are often known as waste but also an important source of black carbon (BC) in the environment, were treated by HCl and HF solution for this study, and recorded as FC and SC, respectively. A series of experiments were carried out to investigate the toxicity of pentachlorophenol (PCP) in sediment, influence of various BCs in sediment with different contents (0%, 0.5%, 1%, 2%, 5% and 10%) on the extractability and toxicity of PCP (50mg/kg), and toxicity of various BC in sediment. The results demonstrated that the PCP exposure to wheat seed exhibited a dose-dependent behavior, and the extractability and toxicity of PCP decreased with the increasing content of BC in sediment. The PCP extractable rate was significantly (P <0.01) influenced by the higher content of BCs. Noticeably, each BC had no toxic but stimulative effect on root elongation and early seedling growth. Furthermore, it was found that the inhibitive effect on the extractability and toxicity of PCP and the stimulative effect on root elongation and early seedling growth caused by SC were more evident than FC. [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: Rice straw charcoal, soot and fly ash (collectively termed “black carbon” or BC), which were found to widely exist in the environment and exhibit strong sorption of many organic compounds, were prepared for this study, and recorded as RC, SC, and FC, respectively. The characterization, sorption isotherm, and the effect of pH (from 3.0 to 9.0) on sorption capacity of each BC were investigated. It is demonstrated that RC possessed the largest surface area (234.9m2/g), the highest porosity (0.4392mL/g), and the largest amount of functional groups (2.995mmol/g) of all. All the Freundlich, Langmuir and Dual-mode model can fit the sorption data of each BC well. The pH value could apparently affect the sorption capacity of pentachlorophenol (PCP) to BCs, which reached maximum value at pH 4.0. Furthermore, in order to validate the effect of pH on desorption capacity, we designed sorption–desorption cycle experiments at pH 9.0 and then pH 7.0, and found that the effect of pH on irreversible sorption and hysteresis effects were significant. As pH value decreasing from 9.0 to 7.0, the irreversible sorption capacities for RC, FC, and SC increased, and the desorption hysteresis index (H) values of PCP increased approximately 3 times for each BC. [ABSTRACT FROM AUTHOR]

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]

Abstract: In this study, considering that Hg2+ in wet flue gas desulfurization (FGD) systems can easily be reduced and then released into atmosphere, causing secondary pollution, the researches about Hg2+ reduction and Hg0 re-emission mechanism were carried out. The effects of several experimental parameters on the reduction were studied, including initial pH, temperature, and concentrations of Cl− and S(IV). Our experimental results indicated that Cl− had a restraining effect on the Hg2+ reduction and Hg0 re-emission, after 24h reaction, only 20.5% of Hg2+ was reduced with 100mM Cl− in simulated desulfurization solution. Cl− can slow Hg2+ reduction and Hg0 re-emissions dramatically through changing reaction mechanism, with formation of new intermediate: ClHgSO3 −, which can decompose to Hg0, but much more slowly than Hg(SO3)2 2− or HgSO3. Simulating the conditions of the practical application (initial pH 5, T =50°C, S(IV)=5mM, Cl− =100mM), we also found that Ca2+, NO3 −, F−, etc. all had obvious effects on reduction rates. Based on the material balance and characteristic of the reactants, the reduction emission mechanism of Hg2+ has been established, providing theoretical basis for industrial application of mercury control in wet FGD systems. [Copyright &y& Elsevier]

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]

• A novel adsorbent (FeMnO x /SBA-15) was successfully synthesized. • SBA-15 functioned as a supporting matrix to disperse Fe-Mn binary oxide. • Calcination treatment could enhance the adsorption capacity of FeMnO x /SBA-15. • FeMnO x /SBA-15 with 45% loading ratio possessed larger specific surface area. • The uptake of arsenic on adsorbents was controlled by surface complexation. Iron-manganese binary oxides (FeMnO x) can remove contaminants from aqueous solutions with high efficiency, and mesoporous silica (SBA-15) is widely used as a supporting material due to its large specific surface area and good stability. In this study, SBA-15 was used to support FeMnO x in the synthesis of a novel arsenic (As) adsorbent (FeMnO x /SBA-15), and its characteristics under different reaction conditions, such as pH, temperature, presence of competing ions, and humic acid, were tested. The results showed that the contaminant adsorption efficiency of the novel adsorbent was better than that of bare FeMnO x , as the addition of SBA-15 decreased the agglomeration effect of FeMnO x. Additionally, FeMnO x /SBA-15 underwent calcination to further enhance its performance. The state of iron and manganese in FeMnO x /SBA-15 and the corresponding arsenic removal efficiency were improved by calcination at 350 °C with an FeMnO x /SBA-15 mass fraction of approximately 45%. Almost 90% of As (50 mL, 5.0 mg L−1) could be removed by 0.2 g L−1 of FeMnO x /SBA-15 (mass ratio of 45% and calcination temperature of 350 °C). The FeMnO x /SBA-15 could regenerate and still be used after four consecutive cycles. The high As sorption capacity, ability to regenerate, and reusability of FeMnO x /SBA-15 confirmed that this adsorbent is promising for treating As-contaminated drinking water. [ABSTRACT FROM AUTHOR]