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In this study, nanosized ordered magnetic mesoporous Fe-Ce bimetal oxides (Nanosized-MMIC) with highly well-ordered inner-connected mesostructure were successfully synthesized through the KIT-6 template method. This Nanosized-MMIC displayed excellent adsorption capacities for As(V), Cr(VI) and AO7, and the corresponding calculated maximum adsorption capacities of material were 111.17, 125.28 and 156.52 mg/g, respectively. As(V) and Cr(VI) removal by Nanosized-MMIC were slightly dependent on the ionic strength but highly solution pH-dependent, the coexistent silicate and phosphate ions competed remarkably with both As(V) and Cr(VI) for the adsorption active site. Mechanisms indicated As(V) and Cr(VI) formed inner-sphere complexes on Nanosized-MMIC interface via the electrostatic interaction and surface complexation, while the total organic carbon (TOC) change demonstrated that AO7 could be removed completely and no organic intermediates formed through the adsorption process. In addition, Nanosized-MMIC also possessed superior adsorption performance in As(V)/Cr(VI)-AO7 binary systems, and the reusable and regeneration properties indicated that the obtained nanomaterials could maintain at a comparatively high level after several recycling. Finally, fixed-bed experiments suggested the Nanosized-MMIC was expected to have a promising excellent nano-adsorbent with high application potential for co-existed toxic heavy metals and organic dyes removal in practical wastewater treatment., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

In this study, the freshly prepared nascent ferrous hydroxide colloids (FHC) were used to eliminate two kinds of inorganic arsenic and simultaneously explore the arsenic speciation in aqueous phase and solid phase interface. The result indicated that when FHC maintained at a lower dosage (5–80 mg Fe/L), the As(III) removal efficiency was greater than that of As(V), which was consistent with the conclusion drawn from the maximum adsorption capacities by the Langmuir model (As(III) and As(V) were 122.63 mg/g Fe and 103.26 mg/g Fe, respectively). Furthermore, HPLC-ICP-MS and XPS analysis from liquid-solid two phase indicated that part of As(III) could be quickly oxidized into As(V) (approximately 5 min), while no As(V) was reduced to As(III) even under the longer reaction time (10 days). This redox transformation behavior of arsenic caused by the mineral transformation of nascent FHC, which formed secondary Fe(II)-Fe(III) (hydr)oxides minerals (newly formed Fe 3 O 4 phase in situ). These results revealed that the nascent FHC have greatly potential practical application in arsenic contaminated groundwater, especially for As(III) removal directly without a pre-oxidation step. [ABSTRACT FROM AUTHOR]

Inorganic arsenic cycling in the natural environment is significantly controlled by manganese/iron oxides, and studying the redox transformation of arsenic in both aqueous and solid phase is therefore essential to understand its environmental toxicity and predict its environmental behavior. Herein, the synthesized magnetic thin-film MnO 2 nanosheet-coated flowerlike Fe 3 O 4 nanocomposites have been used to simultaneously investigate the potential redox transformation of arsenic in aqueous phase and arsenic speciation on the solid phase interface. The results showed the initial Mn/Fe ratio has serious influenced the morphologies, textural properties and uptake of arsenic in aqueous solution. The maximum adsorption capacities of As(III) and As(V) by MF2 were 76.73 mg/g and 120.50 mg/g, respectively. After 10 h reaction, the total arsenic concentration in both As(III)-MF2 system and As(V)-MF2 system far below than that of 10 μg/L, which was setted the maximum guideline concentration value in drinking water by World Health Organization (WHO). HPLC-ICP-MS revealed that in aqueous solution part of As(III) was oxidized into As(V), while As(V) was not reduced into As(III). X-ray absorption near edge structure (XANES) and XPS analysis from solid phase further confirmed that the MnO 2 nanosheet mainly acted as an oxidant, while flowerlike Fe 3 O 4 only played the role as an arsenic species adsorbent. Extended X-ray absorption fine structure (EXAFS) analysis indicated that both As(III) and As(V) formed inner-sphere bidentate binuclear corner-sharing ( 2 C ) complexes with an As-Fe interatomic distance of 3.32–3.34 Å on the interface of As-MF2 solid phase. [ABSTRACT FROM AUTHOR]

Magnetic hollow Fe 3 O 4 -based Mg/Al layered double hydroxide (Fe 3 O 4 @SiO 2 @LDH) was successfully synthesized and subsequently the laboratory scale tests were conducted to systematically investigate the sequestration of roxarsone (ROX) and arsenate (As(V)). Owing to its abundant surface metal hydroxyl (M-OH) groups and exchangeable CO 3 2− groups in the interlayer of MgAl-LDH nanosheets, the obtained Fe 3 O 4 @SiO 2 @LDH exhibited remarkable behavior for As(V) and ROX removal. Both As(V) and ROX could be effectively immobilized at a relatively wide pH range (3–8), and the maximum adsorption capacities of As(V) and ROX were 96.47 and 71.67 mg/g, respectively. Meanwhile, the negligible mutual effect demonstrated the Fe 3 O 4 @SiO 2 @LDH can simultaneously remove inorganic and organic arsenic compounds. The competitive cations/anions (except for PO 4 3− ions) and ionic strength were negligible on As(V) and ROX removal, whereas the inhibitory effect stem from humic acid (HA) seemed to be more seriously for As(V) than that of ROX. Adsorption mechanism of As(V)/ROX were attributed to electrostatic attraction and ion/ligand exchange process, whereas hydrogen bonding and π-π interaction may also involve in the ROX removal. Furthermore, the excellent performance in fix-bed column tests and prominent reusability indicated this magnetic Fe 3 O 4 @SiO 2 @LDH was a promising candidate adsorbent and of great potential application in organic/inorganic As-contamination wastewater treatment. [Display omitted] • Magnetic hollow Fe 3 O 4 -based Mg/Al layered double hydroxide was successfully synthesized. • Adsorption behavior for As(V) and ROX was favorable at acidic and neutral environment. • Simultaneous removal of inorganic and organic arsenic compounds was achieved by Fe 3 O 4 @SiO 2 @LDH. • Remarkable removal and excellent performance of As(V) and ROX in fix-bed column tests. • Surface M-OH groups and the exchangeable CO 3 2− ions involved in the adsorption mechanism. [ABSTRACT FROM AUTHOR]

A series of ordered mesoporous Fe Mn bimetal oxides (OMFMs) were fabricated by using a novel inverse micelle method, and the texture, nanostructure and interface chemistry properties of OMFMs were closely correlated to the calcination temperature. Due to the amorphous regular inner-connected nanostructure and bimetallic synergistic effect, the obtained OMFMs exhibited superior arsenic sequestration performance than pure mesoporous Fe oxides (PMF) and Mn oxides (PMM). The optimum ratio of Fe/Mn and calcination temperature for arsenic removal was 3/1 and 350 °C (OMFM-3), and the maximum As(III) and As(V) adsorption capacities of OMFM-3 were 174.59 and 134.58 mg/g, respectively. Solution pH value negligibly affected the uptake of arsenic (ranged from 3.0 to 7.0), while SiO 3 2−/PO 4 3− ions and humic acid (HA) displayed significant inhibitory effect on arsenic removal by OMFM-3. According to the mechanism of arsenic removal, which simultaneously analyzed the arsenic redox transformation in aqueous phase and on solid phase interface, it was concluded that manganese oxides in OMFM-3 mainly played the role as a remarkable As(III) oxidant in water, whereas iron oxides dominantly acted as an excellent arsenic species adsorbent. Finally, the prominent arsenic sequestration behavior and performance in surface water suggested that OMFM-3 could be a promising and hopeful candidate for arsenic-contaminated (especially As(III)) surface water and groundwater remediation and treatment. Unlabelled Image • A series of OMFMs were successfully fabricated via a novel inverse micelle method. • Calcination temperature affected the nanostructure and surface chemistry of OMFMs. • SiO 3 2−/PO 4 3− ions and HA significantly influenced on both As(III) and As(V) removal. • Redox transformation of arsenic in liquid-solid phase was simultaneously investigated. • Respective role of Fe/Mn oxides in OMFM-3 for arsenic removal was identified. [ABSTRACT FROM AUTHOR]