Inorganic Microporous Membranes for Gas Separation in Fossil Fuel ...

4 Results and discussion
Raman Intensity
752
647
579
800 600 400
Wavenumber/cm -1
104
419
432
450
380
600ºC
500ºC
Figure 71 Raman spectra of the Ti0.5Zr0.5O2 membranes calcined at 500ºC (green) and at 600ºC (blue)
using the excitation of 514.5 nm, 20.6 mW.
4.3.3.3 Amine approach - Organic content in membrane layers
The effective pore size in the layers can be determined by an amorphous film around the
nanocrystals or in combination with the presence of organic residues originating from the
amines. The latter hypothesis was put forward by Duke et al. 94 for carbon remainings
and by Xomeritakis et al. 140 for amine groups in microporous silica membranes.
The carbon content at the outer surface of the membrane layers as determined by XPS
decreases with calcination temperature and is slightly higher than the carbon content of
the bulk material as determined by ICP (Figure 72). However, sputtering the surface with
argon for 2 minutes reduces the carbon content to comparable values. This suggests that
the observed high carbon concentrations originate significantly from atmospheric
contamination. Striking is the agreement between the carbon content trend in the powders
and the layer with increasing ZrO2 in the sample. Both bulk material and membrane layer
show an increase in carbon content with an increasing ZrO2 content. This can be
explained by the slightly higher reactivity of the titanium precursor compared to that of
the zirconium precursor resulting in stronger organic-inorganic bonds.