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Graphical abstract Highlights: • The addition of Mn can promote the formation of amorphous iron oxide in FMBO. • Sb(V) adsorption of amorphous Fe oxide was better than high crystalline Fe oxide. • Sb(V) adsorption rates and capacities of FMBO decreased with reduced Mn content. • FMBO 3 gradually transformed from amorphous to crystalline state during recycling. Abstract Fe-Mn binary oxides (FMBO) with different Fe/Mn molar ratios were synthesized to investigate the influence of the changed iron oxides forms and the manganese oxide on the removal efficacy of Sb(V) from water under neutral pH. The characterization tests by electron microscopy and X-ray diffraction spectroscopy showed that FMBO gradually changed from granular to aciculiform or fibrous structure and their crystalline degree increased with the decreasing Mn content. The ferric oxides in FMBO transformed from 2-L ferrihydrite-like substance with amorphous state to goethite or lepidocrocite with high crystalline as the amount of added Mn reduced during the preparation. The Sb(V) adsorption rates and capacities of FMBO both decreased and the influence of pH on the Sb(V) removal became greater with the decreasing Mn oxide content. All the results indicated that the addition of Mn could greatly improve the Sb(V) removal performance of FMBO through promoting the formation and preventing the transformation of amorphous ferric oxide in FMBO during the preparation, whose Sb(V) adsorption ability was confirmed to be stronger than that of goethite or lepidocrocite. Further exploration indicated the complexation reaction between Sb(V) and amorphous ferric oxide played a key role in Sb(V) adsorption by FMBO. Meanwhile, FMBO with a Fe/Mn molar ratio of 3:1 (FMBO 3) exhibited excellent regeneration performance and the amorphous iron oxide in FMBO 3 gradually transformed into crystalline iron oxide during the consecutive recycling. [ABSTRACT FROM AUTHOR]

A novel amino-functionalized multiwalled carbon nanotube (MWCNTs @SiO 2 -NH 2 ) was prepared via co-condensation using etraethyl orthosilicate and 3-aminopropyl trimethoxysilane for effective removal of Pb(II) from water. The Pb (II) adsorption efficiencies of MWCNTs and MWCNTs@SiO 2 -NH 2 were compared and the change of morphology features was assessed in batch adsorption experiments. The characterization analysis like XRD, FITR and XPS revealed that amino groups were successfully grafted on the MWCNTs. Adsorption results demonstrated that the best TEOS/APTMS loading ratio was about 10:3 based on their solution volume ratio. Compared to the poor Pb(II) adsorption capacity of pristine MWCNTs, the maximum adsorption capacity of MWCNTs@SiO 2 -NH 2 was greatly improved to 147 mg/g after amination treatment. Pb(II) adsorption onto MWCNTs@SiO 2 -NH 2 was strongly pH-dependent and the optimal aqueous pH was about 5. Moreover, the pseudo-second-order kinetics model and Langmuir isotherm model could well describe the Pb(II) adsorption process by MWCNTs@SiO 2 -NH 2 . Thermodynamics analysis illustrated that the Pb(II) adsorption was spontaneous and endothermic. FTIR and XPS analysis of MWCNTs@SiO 2 -NH 2 after adsorption demonstrated the complexation between amino groups and Pb(II) played a vital role in the adsorption mechanism. Findings from the present study suggested that successful Pb(II) removal could be achieved using such novel adsorbent composite with optimized process. [ABSTRACT FROM AUTHOR]

Nanoscale zero-valent iron (nZVI) has high removal efficiency and strong reductive ability to organic and inorganic contaminants, but concerns over its stability and dispersity limit its application. In this study, nZVI was modified with sulfide to enhance Cd(II) removal from aqueous solutions. TEM and SEM analyses showed that sulfide-modified nZVI (S-nZVI) had a core-shell structure of nano-sized spherical particles, and BET results proved that sulfide modification doubled the specific surface area from 26.04 to 50.34 m 2  g −1 and inhibited the aggregation of nZVI. Mechanism analysis indicated that Cd(II) was immobilized through complexation and precipitation. Cd(II) removal rate on nZVI was only 32% in 2 h, while complete immobilization could be achieved in 15 min on S-nZVI, and S-nZVI with an optimal S/Fe molar ratio of 0.3 offered a cadmium removal capacity of about 150 mg g −1 at pH 7 and 303 K. The process of Cd(II) immobilization on S-nZVI was fitted well with pseudo-second-order kinetic model, and the increase of temperature favored Cd(II) immobilization, suggesting an endothermic process. The presence of Mg 2+ and Ca 2+ hindered Cd(II) removal while Cu 2+ did the opposite, which led to the order as Cu 2+  > control > Mg 2+  > Ca 2+ . The removal rate of 20 mg L −1 Cd(II) maintained a high level with the fluctuation of environmental conditions such as pH, ion strength and presence of HA. This study demonstrated that S-nZVI could be a promising adsorbent for Cd(II) immobilization from cadmium-contaminated water. [ABSTRACT FROM AUTHOR]

In this study, a comparative evaluation of synthetic FeS and natural pyrite was performed to investigate their adsorptive potentials toward Hg(II) in aqueous system. Characterization analyses such as BET, SEM and TEM suggested that FeS had porous structures with abundant active sites, while pyrite with a hard and smooth surface relied mainly on surface adsorption to immobilize Hg(II). Results of batch tests revealed that FeS offered much greater Hg(II) maximum adsorption capacity (769.2 mg/g) as compared to pyrite (9.9 mg/g). Both iron sulfides showed high removal efficiency (>96%) with the initial Hg(II) concentration (1 mg/L) at pH = 7.0 ± 0.1, and the effluent could meet the permissible effluent concentration (<50 μg/L). Condition experiments (such as pH, co-ions) proved that the adaptive capacity of FeS was significantly higher than that of pyrite. A pseudo-second-order kinetic model was better able to illustrate the sorption kinetics on both FeS and pyrite (R 2 ≥ 0.9992). XRD and XPS analyses supported that precipitation, ion exchange and surface complexation were main reaction mechanisms involved in the adsorption process. In addition, it was also revealed that the structural changes of FeS before and after adsorption was much larger than pyrite. Findings from this study suggest FeS is a promising candidate for treatment of high-concentration Hg(II)-containing wastewater (<20 mg/L), while pyrite can be applied as a long-term adsorbing material in the immobilization of wastewater containing low Hg(II) concentration (<1 mg/L) due to its cost-effective property and local availability. [ABSTRACT FROM AUTHOR]

In this study, SiO 2 -EDTA was prepared by silanization reaction between N-(trimethoxysilylpropyl) ethylenediamine triacetic acid, trisodium salt (EDTA-silane) and hydroxyl groups for enhanced removal of Pb(II), Pb(II)-Cit (the clathrate generated by Pb(II) and trisodium citrate dehydrate(Cit)) and Pb(II)-EDTA(20%) from aqueous solutions. SiO 2 -EDTA composites were characterized using SEM, TEM, EDX-mapping, FTIR, XPS and TGA analyses. The influence of solution pH, initial concentration, contact time and co-existing interferents were also studied. Results demonstrated that the composite successfully adsorbed 147.52, 107.65 and 124.18 mg g −1 of Pb(II), Pb(II)-Cit, and Pb(II)-EDTA (20%), respectively with the initial Pb(II) concentration of 100 mg L −1 . Kinetics study revealed that the adsorption rate was significantly high at the beginning and then reached to equilibrium within 1.0 h. Moreover, Pb(II) adsorption capacities were found to considerably affected by co-existing cations and not inhibited by natural organic matter (NOM). Characterization analyses confirmed that EDTA was successfully assembled on SiO 2 which had been used as a supporting matrix due to its huge specific surface area. Findings from this study suggested that the present composite could be considered as a promising adsorbent for large scale treatment of wastewater containing elevated Pb(II) concentration. [ABSTRACT FROM AUTHOR]

In this study, EDTA-functionalized Fe 3 O 4 (Fe 3 O 4 @SiO 2 -EDTA) was prepared by silanization reaction between N-(trimethoxysilylpropyl) ethylenediamine triacetic acid (EDTA-silane) and hydroxyl groups for Pb(II) and Cu(II) removal from aqueous solutions. Fe 3 O 4 @SiO 2 -EDTA composites were characterized using SEM, TEM, EDX, FTIR, XPS, TGA and saturated magnetization techniques. Maximum Pb(II) adsorption capacity was found to be 114.94 mg g −1 with SiO 2 /EDTA molar ratio of 2.5:1. The adsorption rate was significantly fast and the equilibrium was reached within 10 min. The optimum pH was recorded to be 5.0. The maximum adsorption capacity of the studied heavy metal ions calculated by Langmuir model followed the order: Cu(II) (0.58 mmol g −1 ) > Pb(II) (0.55 mmol g −1 ) ≈ Ni(II) (0.55 mmol g −1 ) > Cd(II) (0.45 mmol g −1 ). Moreover, Pb(II) and Cu(II) adsorption capacities were not significantly affected by co-existing cations and NOM. These results suggested that this adsorbent can be considered as a promising adsorbent to remove Pb(II) and Cu(II) from wastewaters. [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]

Magnetic biochar is increasingly known as a multi-functional material and the appropriate synthesis method further increase its efficient applications. In this study, the effects of synthesis methods on the fabrication of Kans grass straw/biochar (KGS/KGB) with Fe 3+ /Fe 2+ by chemical co-precipitation and subsequently pyrolyzing at 500 °C for 2 and 4 h were studied in details, and compared their As(III, V) adsorption potentials under different operating conditions. Magnetic biochars (MKGB3 and MKGB4) prepared from KGS revealed of superior Fe 3 O 4 loading, higher As(III, V) adsorption efficiency and saturation magnetization (45.7 Am 2 kg −1 ) than that of KGB (MKGB1 and MKGB2). Moreover, Thermogravimetric analysis (TGA) demonstrated three stages of decomposition and the MKGB3 and MKGB4 generated higher residual mass (>60%) at stage 3 (1000 °C) due to greater Fe 3 O 4 composite in biochar matrix and turned to be thermally more stable. As(III) and As(V) adsorption equilibrium data well fitted in Langmuir model and followed the order: MKGB4 > MKGB3 > MKGB2 > MKGB1. The maximum As(III) and As(V) adsorption capacities were about 2.0 mg g −1 and 3.1 mg g −1 , respectively. The data best fitted in pseudo-second-order ( R 2 > 0.99) rather than pseudo-first-order kinetics model indicating of more complex mechanism. The adsorption of As(III) and As(V) was found to decrease with increasing in ionic strength of competing ions and PO 4 3− was found to strongly inhibit arsenic adsorption. Highest desorption was achieved at pH 13.5 using NaOH. This study suggests that selective adsorbent synthesis method could be useful to prepare effective adsorbent for toxic metals immobilization. [ABSTRACT FROM AUTHOR]

Highlights: [•] Effective electrocatalytic dechlorination of 2,4-D was achieved. [•] Dechlorination efficiency was enhanced by nTiN doped in Pd layer on the electrode. [•] nTiN doping content and Pd loading influenced the dechlorination efficiency. [•] Hydrogen adsorption balance existed between two phases in Pd layer. [•] Active hydrogen atom [H] could be stored in Pd lattice for a period of time. [Copyright &y& Elsevier]

Highlights: [•] nZVI assembled on magnetic Fe3O4/graphene nanocomposites is synthesized. [•] Better dispersion and stability of nZVI are achieved. [•] These nanocomposites exhibit high removal efficiency on Cr(VI). [•] Cr(VI) adsorption and reduction via nZVI-graphene/Fe3O4 battery work synergically. [ABSTRACT FROM AUTHOR]

Cr(VI) is a toxic pollutant and its reduction to relatively less toxic Cr(III) can solve this problem to a greater extent. In the present study, coupled reduction–sorption of Cr(VI) in aqueous solutions using limonite was investigated as a function of pH, limonite dose and particle size. Results demonstrated that the smaller limonite particle size and low pH aqueous medium favored high Cr(VI) removal. Significant Cr(VI) removal (>55±1%) was achieved with 100–200mesh, whereas only 25±0.7% and 10±0.5% removals were attained using 30–40mesh and 20–30mesh, respectively, after 2h reaction. Acid pH proved beneficial and the complete Cr(VI) removal was observed at pH <4.0 compared to that of 10±0.5% at pH9.0. Moreover, above 53±2.5% of Cr(VI) removal rates were maintained in the first three batch experiment runs and then drastically decreased to below 5±0.3% in experiment Run-7. The Brunauer–Emmett–Teller (BET) surface area and sorption capacity of limonite were 35.22m2 g−1 and 10.03mgg−1, respectively. The reaction mechanism demonstrated that under acidic aqueous medium, the dissolved Fe(II) and S(II) on limonite surface reacted with Cr(VI) and formed Cr3S4 and Cr5Si3 precipitates. But the resultant precipitates on limonite surface hindered further Cr(VI) removal and passivated, affirmed in XRD and ESEM analyses. This study suggested that limonite can be used for the effective removal of Cr(VI) from contaminated water environments. [ABSTRACT FROM AUTHOR]

Sulfate in groundwater has been previously shown to change the reactivity of Fe0 in permeable reactive barriers for reducing chlorinated organics. To better understand the effect and mechanism of SO, the degradation of 1,1,1-trichloroethane (TCA) by Fe0 in unbuffered aqueous solutions with and without SO was investigated. In a Fe0-TCA-H2O system with initial pH of 2.0 to 10.0, the maximum removal rate of TCA was achieved at the initial pH 6.0 with pseudo-first-order constant Kobs 9.0 × 10−3/min. But in a Fe0-TCA-Na2SO4-H2O system, the removal rate of TCA decreased remarkably with a reduction in Kobs to 1.0 × 10−3/min, and the pH varied from 6.0 to 9.6, indicating an inhibition of TCA dehydrochlorination by SO. Sulfate remarkably inhibited TCA degradation via changing the route of Fe0 dissolution. It accelerated the dissolution of Fe0 and transformed the intermediate form Fe(OH)ads to Fe2(SO4)ads, which weakened the affinity between Fe and TCA, and thus depressed the degradation of TCA by Fe0. [ABSTRACT FROM AUTHOR]

Abstract: This study describes the chromium (VI) removal in aqueous solution by nanoscale zero-valent iron (nZVI)-Fe3O4 nanocomposites, which were prepared by a novel in situ reduction method. The effects of several factors, including ionic strength, temperature, co-existing anions and cations and natural organic matters were evaluated. The ionic strength was found to be insignificant to the removal efficiency, while temperature was critical. With the increase in temperature from 10–40°C, 32% removal efficiency increased within 2h from 49.96%. Most anions hindered the reaction, especially in high concentration, such as and , causing a drop of the removal efficiency from 66.48% to 57.47% and 59.93% respectively. In contrast, both cations and moderate natural organic matter facilitated the removal of Cr(VI). It is noteworthy that calcium hardness can greatly promote the reaction, 100% removal efficiency was achieved within 90min and the rate constant k 2 reached 0.528gmg−1 min−1 after adding 40mgL−1 Ca2+, which was ten times more than that in other cases. Possible mechanism was presented, and TEM, SEM and FITR analyses were used to verify these speculations. Hopefully, these results can contribute to a better development of the water treatment facilitates for nZVI-Fe3O4 composites, maintaining its high efficiency in real aqueous environment. [Copyright &y& Elsevier]

Abstract: Water pollution caused by ammonia nitrogen has attracted a great attention as its toxicity affects both the environment and human health. The objective of this paper was to investigate the adsorption behavior of NH4 +-N from aqueous solution by activated carbons prepared from rice husk. The physico-chemical properties of the activated carbon were characterized by Brunauer-Emmett-Teller (BET) test, Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). It was found that the NH4 +-N adsorption on the rice husk derived carbons was dependent on adsorbent dosage and solution pH. The adsorption kinetics and isotherms of NH4 +-N by rice husk carbon were also investigated, and good correlation coefficients were obtained for the pseudo-second order kinetic equation. Dubinin-Radushkevitch (D-R) adsorption isotherm model could better describe the adsorption behavior of NH4 +-N on the rice husk carbon. Calculated by D-R model, the adsorption course of NH4 +-N on the rice husk carbon was favored chemical ion-exchange mechanism. Moreover, the activated carbon adsorbed NH4 +-N was highly fertilizer conservation especially for the nitrogen element. It was proposed that the amount of removed NH4 +-N from aqueous solutions would increase evidently treated by rice husk carbon if combined with biological method. [Copyright &y& Elsevier]

Abstract: The electrochemical reductive dechlorination of 2,4-dichlorophenoxyacetic acid (2,4-D) in an aqueous solution was investigated at ambient temperature using a palladium/nickel foam (Pd/Ni foam) electrode in batch mode experiments. The catalytic electrode prepared using the standard chemical deposition method was further characterized using X-ray diffraction and scanning electron microscopy. It was observed that the reaction followed a pseudo-first-order kinetics model, the magnetic agitator-supported system could achieve 87% removal of 2,4-D within 4h, which is 16% higher than the efficiency obtained under a nitrogen atmosphere. No organic intermediates other than phenoxyacetic (PA), o-chlorophenoxyacetic acid (o-CPA) and p-chlorophenoxyacetic acid (p-CPA) were observed to be generated during the reaction. The dechlorination efficiency depended on several factors including the current density, the palladium loading and the initial concentrations of the supporting NaCl electrolyte and the 2,4-D. The palladium loading and the NaCl concentration had a greater effect on the dechlorination kinetics of 2,4-D. Furthermore, the efficiencies of dechlorination and PA formation could be improved by optimizing the reaction system by modifying the ventilation conditions. [Copyright &y& Elsevier]

Abstract: For the first time, nanoscale zero-valent iron (nZVI)–Fe3O4 nanocomposites, prepared by an in situ reduction method, are employed for chromium(VI) removal in aqueous environment. 96.4% Cr(VI) could be removed by these novel materials within 2h under pH of 8.0 and initial Cr concentration of 20mgL−1, compared with 48.8% by bare nFe3O4 and 18.8% by bare nZVI. Effects of several factors, including mass composition of nZVI–Fe3O4 nanocomposites, initial pH and Cr(VI) concentration, were evaluated. The optimal ratio of nFe3O4 to nZVI mass lies at 12:1 with a fixed nZVI concentration of 0.05gL−1. Low pH and initial Cr(VI) concentration could increase both the Cr(VI) removal efficiency and reaction rate. Corresponding reaction kinetics fitted well with the pseudo second-order adsorption model. Free energy change (ΔG) of this reaction was calculated to be −4.6kJmol−1 by thermodynamic study, which confirmed its spontaneous and endothermic characteristic. The experimental data could be well described by the Langmuir and Freundlich model, and the maximum capacity (q max) obtained from the Langmuir model was 100 and 29.43mgg−1 at pH 3.0 and 8.0, respectively. The reaction mechanism was discussed in terms of the mutual benefit brought by the electron transfer from Fe0 to Fe3O4. [Copyright &y& Elsevier]