Particle characterisation

Team
Ralf Kaegi, Brian Sinnet, Markus Boller

Goal
Application of nano-technologies for the characterization of suspended submicron particles by:
- Performing analysis and characterization of all suspended material in water sources at the nanometer scale, by using a combination of both SEM (Scanning Electron Microscopy) and AFM (Atomic Force Microscopy).
- Revealing the relationship between suspended material properties and water treatment processes.

Description
The analysis of colloids at the scale of one particle is quite challenging. Although, inorganic colloids (ferrihydrite, amorphous manganese oxides or clay particles) can be analyzed at the nanometer scale thanks to high-resolution microscopy such as Transmission Election Microscopy (TEM) with analytical capabilities (x-ray fluorescence, electron energy loss), an organic colloids’ physical composition in three dimensions are not observed. Atomic Force Microscopy (AFM) has shown its potential for that purpose. Nevertheless, AFM gives morphological information and can show mapping of certain ion groups, but the elemental composition is not achievable with this technique.
SEM (Scanning Electron Microscopy) has demonstrated its capabilities for environmental particles in showing a simulated three-dimensional image and qualitative composition. Nevertheless, due to the environment of the SEM, specimens are analyzed under a vacuum, therefore dry, and can suffer bond changes caused by the electron beam. The morphology is then affected and the formation processes might be missing (real fractal dimension etc.). On the other hand, details of the structure such as crystallinity, composition and even the oxidation state can be obtained.
AFM physically probes the sample surface without causing bond changes or damage to the specimen. Dragging the probe along the sample surface gives a true three-dimensional image; which is only capable by the SPM (Scanning Probe Microscopy) technique. It has been shown that fine and fragile structures such as DNA, organic macromolecules or details on aggregates are preserved. The ability of imaging the particles in their own environment (ambient temperature and pressure, or in a liquid) is essential for the characterization of water samples. In addition, chemical information can be measured to a certain extent (cohesion forces, specific ion groups). The SEM and AFM compliment each other greatly for structural, morphological and three-dimensional details never attained before in water treatment processes until now.