Membrane Preparation
Cellulose solution was prepared according to
previously reported methods [19]. An amount of
23.3 g cellulose was dispersed in 400 g aqueous
solution of 8 wt% NaOH/6.5 wt% thiourea/8 wt%
urea, then pre-cooled to -8°C, followed by vigorous
stirring for 3 min at room temperature. After 3 min,
the temperature of the solution was controlled
between -2 and 0°C using a salt-ice bath and the
mixture was vigorously stirred for 17 min to obtain
transparent cellulose dope containing 5.5 wt%
cellulose. The cellulose dope was subjected to
centrifugation at 10000 rpm for 20 min at 5-10°C in
order to exclude the slightly remaining undissolved
part and to carry out the degasification. The resulting
transparent solution was immediately cast onto a glass
plate at a thickness of 200 μm and then immersed into
coagulants (2000 mL) for the desired time at the
desired temperature. The resulting wet membranes
were washed with running water and finally air-dried
at ambient temperature. A series of aqueous solutions
of 5 wt% H2SO4, 5 wt% HCl ,5 wt% HAc, 5 wt%
H2SO4/5 wt% Na2SO4, 10 wt% Na2SO4, 10 wt%
(NH4)2SO4 and 10 wt% NH4Cl and CH3CH2OH
(abs.) were examined as coagulants.