A novel electrocatalytic membrane reactor was designed in this study to minimize or
eliminate the fouling effect, a significant challenge to membrane filtration process, and
improve permeate water quality with the contribution of the electrochemical reactions and
electrophoresis. The electrocatalytic membrane was fabricated by using a facile thermal
decomposition from the mixtures of chloride precursor solution. The coated membrane
surface was employed as an anode in the hybrid electrochemical and membrane filtration
system. A kind of general DSA material of ternary oxide (Ir-Sb-Sn) was coated on the α-Al
2O
3
membrane surface and tested first. The catalytic coating showed high hydrophilicity and good
adherence with the membrane substrate. The ternary oxide in the catalytic coating was
characterized to be IrO
2-SnO
2-Sb
2O
3.25 (or IrO
2-SnO
2-(Sb
2O
3)
3(SbO
2)
2). Furthermore, a novel
IrO
2-Sb
2O
3.25 membrane with 1D nanostructure has been successfully fabricated. The distinct
1D morphology of catalytic coating shows much rougher surface and higher porosity. The
surface area is 149.22 m
2/g, which is almost 2.37 times that of IrO
2-SnO
2-Sb
2O
3.25 membrane.
Moreover, electrically conducting Ru was introduced into 1D IrO
2-Sb
2O
3.25 coating in order to
improve the electrical property and electrochemical performance. In particularly, the flat
resistivity at the Ir/Sb/Ru molar ratio of 1:1:0.25 with the catalyst loading of 40.2 g/m
2 is
equal to 22.5 Ω/sq, which is only 18.2% of 122 Ω/sq in IrO
2-SnO
2-Sb
2O
3.25 membrane.
Similarly, the experimental EIS data show that the charge-transfer resistance (R
ct) is equal to
17.1 Ω cm
2 in 1D IrO
2-RuO
2-Sb
2O
3.25 membrane, which is only 25.8 % of 66.05 Ω cm
2 in
IrO
2-SnO
2-Sb
2O
3.25 membrane.
Higher pure water permeability was achieved in the 1D IrO
2-RuO
2-Sb
2O
3.25 membrane due to
higher porosity, in comparison with IrO
2-SnO
2-Sb
2O
3.25 membrane. The water flow resistance
of 1D IrO
2-RuO
2-Sb
2O
3.25 membrane is only 80% of that of IrO
2-SnO
2-Sb
2O
3.25 membrane
with the same catalyst loading of 35 g/m
2. The extents of fouling of both catalytic membranes
for oily wastewater treatment were reduced due to their higher hydrophilicity in comparison
with the original uncoated Al
2O
3 membrane.
Electrocatalytic reactions were successfully achieved on the catalytic membrane surface when
it was employed as the anode in the electrocatalytic membrane reactor. The extent of fouling
was reduced by at least 20% after 30 min of operation, when 0.15A current was applied. The
generated gas bubbles may prevent the oily pollutants from adsorption and the reactive
intermediates may electrochemically oxidize the oily foulants on the membrane surface. The
time-average permeate flux increased by almost 44% owing to the contribution of
electrochemical reactions. The water quality of permeate solution for electrocatalytic
membrane was further enhanced with the increasing in the applied current. The COD
rejections are 95.8% and the permeate COD are 22.3 mg/L at the applied currents of 0.15A.
The membrane fouling also can be significantly minimized by electrophoresis, when no
appreciable current was passed through the electrocatalytic membrane reactor with the
catalytic membrane surface as the anode. Only 25.2% drop in permeate flux was observed
after 2.8 h of operation when the 13 V/cm electric field was applied, and the highest permeate
volume of 1240 mL was achieved. In contrast, the permeate flux declined rapidly and
decreased by 90% after 40 min of operation without the assistance of the electrophoresis. The
time-average permeate flux is around 414 L/m
2·h·bar, which is over 6 times of that without
electric field. The permeate COD and COD rejections are 15.9 mg/L and 97.0%, respectively.
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