Analytical electron microscopy as a tool for accessing colloid formation process in natural waters

Abstract

SummaryAnalytical electron microscopy was used to characterize aquatic iron-rich colloids. We focused our attention on a redox transition medium in the drainage water of a peat soil. In the anoxic peat water, observations by transmission electron microscopy and associated energy dispersive analyses (TEM-EDS) highlight the presence of spherical entities ( ∼ 100-600 nm), containing only traces of iron. The increase of dissolved oxygen concentration favours the formation of iron oxy(hydr)oxides. In the oxygenated drain, particles with the same morphology and size range are present. Statistical TEM-EDS analyses show that they represent the only colloidal form of iron in the drain samples. Nevertheless, although Fe-K peaks appear clearly on EDS spectra, the proportion of iron in these colloids reaches at most 4% at. (whereas C + O > 90% at.). Structural information completes this study. Both electron spectroscopic imaging (ESI) and electron energyloss spectroscopy (EELS) reveal the disparity between element distributions within the drain entities. Iron and calcium are preferably distributed on the outer sphere of the particle, whereas carbon and oxygen follow the theoretical variation of the signal intensity within a plain sphere. The implication of organic matter as nucleation site for iron precipitation is spectacularly demonstrated by the presence of nanometre-sized iron-rich phases highlighted by EELS line scans.

Size and composition of inorganic colloids in a peri-alpine, glacial flour-rich lake

“…For instance, transmission electronic microscopy (TEM) coupled with energy dispersive spectroscopy (EDS) is frequently used, particularly in oxide studies (Lienemann et al, 1997;Perret et al, 2000). However, results on aluminosilicates are often only semi-quantitative and are mostly confined to a statement that 'clays' are present on the basis of some element ratios, in particular Si:Al (Bishop and Biscaye, 1982;Bernard et al, 1986;Mondi et al, 2002).…”

Coupled Heterojunction Sn2Ta2O7@SnO2: Cooperative Promotion of Effective Electron–Hole Separation and Superior Visible-light Absorption

“…It is noted that the shapes of EDS line scans for Sn and Ta were similar and had a flat central region in the position of 215 nm to 500 nm, giving an evidence for hollow sphere structure, as reported elsewhere. 52,53 Moreover, Ta element can be hardly detected in the ranges of 200 nm to 215 nm and 505 to 520 nm. It means that there were only the species composed by Sn and O elements locating on the outer layers of the spherical shell.…”

Analysis and Characterization of Manufactured Nanoparticles in Aquatic Environments

“…These studies are generally performed on aquatic colloids with a lower size that extends well into the nanoscale size range ( < 100 nm). Examples include rather general descriptions of aquatic colloids from various environments (Leppard, 1992 ;Webb et al , 2000 ;Mondi et al , 2002 ;Lienemann et al , 1997 ;Chanudet and Filella, 2008 ) as well as detailed investigations on colloids such as iron colloids (Perret et al , 2000 ;Leppard et al , 1989 ;Lienemann et al , 1999 ;He et al , 1996 ;Tipping et al , 1981Tipping et al , , 1982Fortin et al , 1993 ) or marine snow .…”