Functionalization
of a Membrane Sublayer Using Reverse Filtration of Enzymes and Dopamine
Coating
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Abstract
High
permeability, high enzyme loading, and strong antifouling ability
are the desired features for a biocatalytic membrane to be used in
an enzymatic membrane reactor (EMR). To achieve these goals, the membrane
sublayer was enriched with laccase by reverse filtration in this case,
and the resulting enzyme-loaded sublayer was covered with a dopamine
coating. After membrane reversal, the virgin membrane skin layer was
facing the feed and the enzymes were entrapped by a polydopamine network
in the membrane sublayer. Thus, the membrane sublayer was functionalized
as a catalytically active layer. The effects of the original membrane
properties (i.e., materials, pore size, and structure), enzyme type
(i.e., laccase and alcohol dehydrogenase), and coating conditions
(i.e., time and pH) on the resulting biocatalytic membrane permeability,
enzyme loading, and activity were investigated. Using a RC10 kDa membrane
with sponge-like sublayer to immobilize laccase with dopamine coating,
the trade-off between permeability and enzyme loading was broken,
and enzyme loading reached 44.5% without any permeability loss. After
85 days of storage and reuse 14 times, more than 80% of the immobilized
laccase activity was retained for the membrane with a dopamine coating,
while the relative activity was less than 40% without the coating.
The resistance to high temperature and acidic/alkaline pH was also
improved by the dopamine coating for the immobilized laccase. Moreover,
this biocatalytic membrane could resist mild hydrodynamic cleaning
(e.g., back-flushing), but the catalytic ability was reduced by chemical
cleaning at extreme pH (e.g., 1.5 and 11.5). Since the immobilized
enzyme is not directly facing the bulk of EMRs and the substrate can
be specifically selected by the separation skin layer, this biocatalytic
membrane is promising for cascade catalytic reactions