C. Aubry, M.T. Khan, A.R. Behzad, D.H. Anjum, L. Gutierrez, J.P. Croue
Desalination, volume 333, issue 1, pp. 118125, (2014)
The intact cross-section of two fouled reverse osmosis
membranes was characterized using a scanning transmission electron
microscope (STEM) equipped with an electron energy dispersive
spectroscope (EDS). Focused ion beam (FIB) was used to prepare a thin
lamella of each membrane. These lamellas were then attached to a TEM
grid for further STEM/EDS analysis. The foulant in sample A was mainly
inorganic in nature and predominantly composed of alumino-silicate
particles. These particles were surrounded by carbon at high
concentrations, indicating the presence of organic materials. Iron was
diffusely present in the cake layer and this could have enhanced the
fouling process. The cake layer of membrane B was mainly consisted of
organic matter (C, O, and N representing 95% of the total elemental
composition) and organized in thin parallel layers. Small concentrations
of Si, F, Na, Mg, and Cl were detected inside the active layer and
support layer of the membrane. Due to the high
sensitivity of the cake layer of membrane A to the electron beam,
STEM/EDS line analyses might have been performed on large areas. On the
other hand, the cake layer of sample B was resistant to the electron
beam and the resolution of STEM/EDS was gradually improved until
obtaining a resolution of 25 nm.