Surface chemical and selective flocculation studies on iron oxide and silica suspensions in the presence of xanthan gum

AbstractIn situbioremediation to achieve immobilization of toxic metals and radionuclides or detoxification of chlorinated solvents relies on electron donor additions. This practice promotes microbial Fe(III)-oxide mineral reduction that could change soil pore structure, release soil colloids, alter matrix surface properties, and cause the formation of secondary (i.e., reduced) Fe-mineral phases. These processes in turn may impact rates of bioremediation, groundwater quality, and ultimately contaminant fate. Continuous flow columns packed with water-stable soil aggregates high in Fe-oxides were infused with artificial groundwater containing acetate as electron donor and operated for 20 or 60 days inside an anoxic chamber. Soluble Fe(II) and soil colloids were detected in the effluent within one week after initiation of the acetate addition, demonstrating Fe(III)-bioreduction and colloid formation. Br-, 2,6-difluorobenzoate (DFBA), and silica-shelled silver nanoparticles (SSSNP) were selected as diffusible tracer, low-diffusible tracer, and non-diffusible nanoparticles, respectively, to perform transport experiments before and after the active 20-day bioreduction phase, with an aim of assessing the changes in soil structure and surface chemical properties resulting from Fe(III)-bioreduction. The transport of diffusible Br-was not influenced by the Fe(III)-bioreduction as evidenced by identical breakthrough curves before and after the introduction of acetate. Low-diffusible DFBA showed earlier breakthrough and less tailing after the bioreduction, suggesting alterations in flow paths and surface chemical properties of the soils. Similarly, non-diffusible SSSNP exhibited early breakthrough and enhanced transport after the bioreduction phase. Unexpectedly, the bioreduction caused complete retention of SSSNP in the soil columns when the acetate injection was extended from 20 days to 60 days, though no changes were observed for Br-and DFBA during the extended bioreduction period. The large change in the transport of SSSNP was attributed to the enhancement of soil aggregate breakdown and soil colloid release causing mechanical straining of SSSNP and the exposure of iron oxide surfaces previously unavailable within aggregate interiors favorable to the attachment of SSSNP. These results demonstrate that microbial activity can affect soil properties and transport behaviors of diffusivity-varying solutes and colloids in a time dependent fashion, a finding with implication for interpreting the data generated from soil column experiments under continuous flow.HighlightsFe(III)-bioreduction causes time-dependent aggregate breakdown and colloid release.Short-term bioreduction alters soil aggregate surface chemistry and tracer transport.Electron donor amendment enhances transport of nanoparticle tracer.

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Thermogravimetry and Mass Spectrometry of Extractable Organics from Manufactured Nanomaterials for Identification of Potential Coating Components

Materials ◽

10.3390/ma12223657 ◽

2019 ◽

Vol 12 (22) ◽

pp. 3657 ◽

Cited By ~ 3

Author(s):

Per Axel Clausen ◽

Vivi Kofoed-Sørensen ◽

Asger W. Nørgaard ◽

Nicklas Mønster Sahlgren ◽

Keld Alstrup Jensen

Keyword(s):

Mass Spectrometry ◽

Iron Oxide ◽

Volatile Organic Compounds ◽

Organic Compounds ◽

Organic Coating ◽

Surface Chemical ◽

Chemical Modifications ◽

Manufactured Nanomaterials ◽

Volatile Organic ◽

Polymeric Compounds

Manufactured nanomaterials (MNMs) often have a surface-chemical modification in order to tailor their physicochemical properties, including also powder properties and miscibility. Surface-chemical modifications may influence the toxicological properties of the MNM, but the specific chemistry and extent are rarely described in detail in suppliers’ technical data sheets. Chemical and quantitative information on any surface-chemical treatment, coating and functionalization are required for chemicals registration in Europe. Currently there is no globally accepted and documented approach to generate such data. Consequently, there is a continued research need to establish a structured approach to identify and quantify surface-chemical modifications. Here we present a tiered approach starting with screening for mass-loss during heating in a furnace or thermogravimetric analysis (TGA) followed by solvent extraction, and analysis by several mass spectrometry (MS) techniques depending on the target analytes. Thermal treatment was assumed to be able to quantify the amount of organic coating and MS was used to identify the extractable organic coatings after pressurized liquid extraction (PLE) using methanol at 200 °C. Volatile organic compounds in extracts were identified with gas chromatography and MS (GC-MS), non-volatile organic compounds with liquid chromatography MS (LC-MS), and polymeric compounds with matrix-assisted laser desorption ionization time-of-flight MS (MALDI-TOF-MS). The approach was demonstrated by analysis of 24 MNM, comprising titanium dioxide, synthetic amorphous silica, graphite, zinc oxide, silver, calcium carbonate, iron oxide, nickel-zinc-iron oxide, and organoclay. In extracts of 14 MNMs a range of organic compounds were identified and the main groups were silanes/siloxanes, fatty acids, fatty acid esters, quaternary ammonium compounds and polymeric compounds. In the remaining 10 MNMs no organic compounds were detected by MS, despite the fact an organic coating was indicated by TGA.

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Analytical Electron Microscopy of Ion-Implanted Metals

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010011831x ◽

1985 ◽

Vol 43 ◽

pp. 282-285

Author(s):

D.I. Potter ◽

M. Ahmed ◽

K. Ruffing

Keyword(s):

Electron Microscopy ◽

Ion Implantation ◽

Friction And Wear ◽

Analytical Electron Microscopy ◽

Chemical Compositions ◽

Surface Chemical ◽

Near Surface ◽

The Past ◽

Analytical Electron ◽

Property Changes

Ion implantation, used extensively for the past decade in fabricating semiconductor devices, now provides a unique means for altering the near-surface chemical compositions and microstructures of metals. These alterations often significantly improve physical properties that depend on the surface of the material; for example, catalysis, corrosion, oxidation, hardness, friction and wear. Frequently the mechanisms causing these beneficial alterations and property changes remain obscure and much of the current research in the area of ion implantation metallurgy is aimed at identifying such mechanisms. Investigators thus confront two immediate questions: To what extent is the chemical composition changed by implantation? What is the resulting microstructure? These two questions can be investigated very fruitfully with analytical electron microscopy (AEM), as described below.

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TEM observation of iron oxide pillars in montmorillonite

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100177544 ◽

1990 ◽

Vol 48 (4) ◽

pp. 882-883

Author(s):

H. Mori ◽

Y. Murata ◽

H. Yoneyama ◽

H. Fujita

Keyword(s):

Aqueous Solution ◽

Iron Oxide ◽

Fine Particles ◽

Aqueous Suspension ◽

Volume Ratio ◽

Exchange Capacity ◽

Nano Composites ◽

Pillared Montmorillonite ◽

Topographic Features ◽

Transmission Electron

Recently, a new sort of nano-composites has been prepared by incorporating such fine particles as metal oxide microcrystallites and organic polymers into the interlayer space of montmorillonite. Owing to their extremely large specific surface area, the nano-composites are finding wide application[1∼3]. However, the topographic features of the microstructures have not been elucidated as yet In the present work, the microstructures of iron oxide-pillared montmorillonite have been investigated by high-resolution transmission electron microscopy.Iron oxide-pillared montmorillonite was prepared through the procedure essentially the same as that reported by Yamanaka et al. Firstly, 0.125 M aqueous solution of trinuclear acetato-hydroxo iron(III) nitrate, [Fe3(OCOCH3)7 OH.2H2O]NO3, was prepared and then the solution was mixed with an aqueous suspension of 1 wt% clay by continuously stirring at 308 K. The final volume ratio of the latter aqueous solution to the former was 0.4. The clay used was sodium montmorillonite (Kunimine Industrial Co.), having a cation exchange capacity of 100 mequiv/100g. The montmorillonite in the mixed suspension was then centrifuged, followed by washing with deionized water. The washed samples were spread on glass plates, air dried, and then annealed at 673 K for 72 ks in air. The resultant film products were approximately 20 μm in thickness and brown in color.

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