2-Mercaptobenzothiazole doped chitosan/11-alkanethiolate acid composite coating: Dual function for copper protection

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Applied
Surface
Science
257 (2011) 10529–
10534
Contents
lists
available
at ScienceDirect
Applied
Surface
Science
j our
nal
ho
me
p age:
www.elsevier.com/loc
ate/apsusc
2-Mercaptobenzothiazole
coating:
doped
chitosan/11-alkanethiolate
acid
composite
Dual
function
for
copper
protection
Qi
Baoa,b,
Dun
Zhanga,∗,
Yi
Wana,b
aShandong
bGraduate
Provincial
Key
Laboratory
of
Corrosion
Science,
Institute
of Oceanology,
Chinese
Academy
of Sciences,
7 Nanhai
Road,
Qingdao
266071,
China
School
of
Chinese
Academy
of
Sciences,
19 (Jia)
Yuquan
Road,
Beijing
100039,
China
a
r
t
i
c
l
e

i
n
f
o
Article
Received
Received
Accepted
Available online 14 July 2011
history:
23 November
2010
in revised
form
1 July
2011
6 July
2011
Keywords:
Copper
2-mercaptobenzothiazole
Corrosion
Microbiologically
influenced
corrosion
a
b
s
t
r
a
c
t
Chitosan
has
which
by
ability
potentiodynamic
the
of
energy
endows
biologically
feature
SRB
better
(CS)
hydrogel
loaded
with
the
well-known
corrosion
inhibitor
2-mercaptobenzothiazole
(MBT)
been
introduced
into
a
composite
coating
to
improve
copper
protection.
This
composite
coating,
has
both
anticorrosion
and
antibacterial
properties,
was
fabricated
onto
the
surface
of
copper
combining
a
simple
self-assembled
monolayer
technique
with
a
sol–gel
method.
The
anti-corrosion
of
the
coating
in
3.5
wt.%
NaCl
solution
was
investigated
by
electrochemical
methods
including
polarization
and
electrochemical
impedance
spectroscopy.
The
protection
efficiency
of
coating
is
97.70%,
calculated
on
the
basis
of
the
corrosion
current
density.
The
stability
and
integrity
the
composite
coating
were
evaluated
by
field
emission
scanning
electron
microscopy
(FESEM)
and
dispersive
spectrometry
(EDS).
The
FESEM
and
EDS
results
suggest
that
the
composite
coating
the
copper
substrate
with
antibacterial
properties,
as untreated
bare
copper
underwent
micro-
influenced
corrosion
in
the
presence
of
sulphate
reducing
bacteria
(SRB).
This
antibacterial
was
further
confirmed
by
the
SRB
culture
method.
In
a
3.5%
NaCl
solution
and
highly
corrosive
culture
media,
the
as-prepared
CS
based
composite
coating
gave
corrosion
protection
by
exhibiting
barrier
effects
against
the
attack
Crown Copyright ©
of aggressive
environments.
2011 Published by Elsevier B.V. All rights reserved.
1.
Introduction
Copper
sion
electrical
systems
sion
as
copper
or
A
chemisorption
and
a number
a simple
shape
tionally,
design
provide
of
and
its
alloys
exhibit
good
mechanical
properties,
corro-
resistance,
antifouling
properties,
and
excellent
thermal
and
conductivity,
and
play
important
roles
in heating-cooling
and
microelectronic
industries
[1–3]. Nevertheless,
corro-
susceptibility
is confirmed
when
oxygen
or
corrosive
ions,
such
chlorides,
nitrates,
sulphates,
and
sulphide
ions,
are
present
in a
system
[4,5]. Thus,
determination
of
methods
to minimize
prevent
the
corrosion
of
copper
is of
corrosion
great
significance.
prevention

convenient

approach

to
is
the
of
alkanethiols
onto
copper
surfaces
to form
dense
ordered
self-assembled
monolayers
(SAMs)
[6–8]. SAMs
offer
of
attractive
advantages
over
other
methods,
such
as
forming
process,
and
the
ability
to coat
objects
of
any
while
enabling
strong
adhesion
onto
the
metal
surface.
Addi-
the
surface
property
of
such
films
can
be
tailored
by
the
and
synthesis
of
suitable
adsorbates
[9].
Although
SAMs
can
significant
protection
to substrates
across
a wide
range
environments,
they
are
susceptible
to gradual
destruction
in
∗Corresponding
E-mail
author.
Tel.:
+86
532
82898960;
fax:
+86
532
82898960.
address:
zhangdun@qdio.ac.cn
(D.
Zhang).
chlorine-containing
effects
Numerous
enced
particularly
nontraditional
microorganisms
cant.
the
It
that
sion
conditions.
Chitosan
used
carriers,
[13].
CS
media
is
This
[14,15].
In
rier
solutions,
which
greatly
limits
their
protective
[10].
industries
have
reported
microbiologically
influ-
corrosion
(MIC)
problems
[11]. The
cooling
industry
is
susceptible
to MIC
because
of
the
increased
use
of
water
sources.
Generally,
the
toxicity
of
copper
to
has
led
to the
belief
that
MIC
of
copper
is
insignifi-
But
the
fact
is
that
sulphate
reducing
bacteria
(SRB)
are
one
of
prevalent
causes
of
corrosion
of
cooling
system
materials
[12].
is
therefore
of
great
importance
to develop
antibacterial
coatings
are
stable,
environmentally
benign,
and
provide
good
corro-
resistance
to improve
copper
performance
under
corrosive
(CS),
a natural
polycationic
copolymer,
has
been
widely
in medical
and
pharmaceutical
applications,
such
as
in drug
tissue
engineering
materials,
and
antimicrobial
agents
With
one
amino
group
in the
repeating
hexsamide
residue,
becomes
soluble
by
protonation
of
the
–NH2in aqueous
acidic
(pH
< 6),
and
possesses
positive
charges.
When
the
pH
raised
to above
6.5,
CS
amino
groups
become
deprotonated.
polysaccharide
can
then
form
an
insoluble
hydrogel
network
this
study,
we
use
a CS
hydrogel
as both
an inhibitor
car-
and
a bacteriostatic
matrix
to determine
its
effects
against
the
0169-4332/$
doi:10.1016/j.apsusc.2011.07.034
– see
front
matter.
Crown Copyright ©
2011 Published by Elsevier B.V. All rights reserved.

Page 3

Author's personal copy
10530
Q.
Bao
et al.
/ Applied
Surface
Science
257 (2011) 10529–
10534
gradual
to
immediately
Furthermore,
surfaces
destruction
of
SAM
and
MIC.
The
CS
hydrogel
is
expected
slowly
release
its
loaded
inhibitor
to heal
active
defect
sites
after
the
immersion
of
SAMs
into
halide
salt
solutions.
CS
is served
as
a
bacteriostatic
component
to protect
from
or
to kill
corrosion
bacteria.
2.
Materials
and
methods
2.1.
Materials
CS
(molecular
weight
= 2100
kDa,
deacetylation
degree
= 90.6%)
was
11-Mercaptoundecanoic
Aldrich
and
from
purification.
water
The
was
resin,
experiments,
supplied
20
Prior
with
smooth
with
obtain
water,
purchased
from
Jinhu
Crust
Product
Co.,
Ltd.
(Qingdao,
China).
acid
(MUA)
was
purchased
from
Sigma-
Co.
and
used
as
received.
2-Mercaptobenzothiazole
(MBT)
other
chemicals
were
of
analytical
reagent
grade,
obtained
Shanghai
Chemical
Reagent
Co.,
Ltd.,
and
used
without
further
All
aqueous
solutions
were
prepared
using
ultra-pure
(Millipore).
working
electrode
used
for
electrochemical
measurements
an
8.0
mm-diameter
copper
rod
(>99.5
wt.%)
sealed
with
epoxy
leaving
a circular
cross-section
(0.50
cm2) exposed.
For
MIC
a polycrystalline
copper
(>99.5
wt.%)
substrate
was
as
a sheet
approximately
1 mm
thick,
and
then
cut
into
× 30
mm
coupons.
to each
experiment,
the
copper
specimens
were
polished
1200#
and
2000#
emery
paper
until
their
surfaces
were
and
mirror-like.
The
copper
samples
were
then
degreased
anhydrous
ethanol,
polished
with
85%
phosphoric
acid
to
a fresh
and
oxide-free
copper
surface,
rinsed
with
ultra-pure
and
finally
dried
under
a
stream
of
N2.
2.2.
Bacteria
and
culture
Seed
bacteria
were
isolated
from
marine
sludge
collected
from
the
collected
Modified
contained
phosphate,
calcium
1
amount
121◦C for
sterilized
In
Bohai
Sea
of
China.
The
filtered
seawater
used
in this
work
was
from
Huiquan
Bay
in Qingdao,
China.
Postgate’s
culture
solution
was
used.
This
solution
2.0
g magnesium
sulphate,
0.5
g dipotassium
hydrogen
1.0
g ammonium
chloride,
0.5
g sodium
sulphate,
0.1
g
chloride,
1.0
g yeast
extract,
and
4.0
mL
sodium
lactate
in
L seawater.
The
pH was
adjusted
to 7.0
using
the
appropriate
of
sodium
hydroxide
before
the
solution
was
autoclaved
at
20
min.
After
cooling,
the
SRB
culture
was
incubated
in
glass
bottles
and
kept
at a constant
temperature
of
30◦C.
the
antibacterial
test,
the
pH
was
adjusted
to 6.0
to facilitate
CS
solvency.
iron(II)
tured
later.
acid
into
parallel
Bacterial
growth
was
confirmed
by
0.5
g/L
ammonium
sulphate
hexhydrate
and
0.1
g/L
ascorbic
acid.
If the
cul-
SRB
were
still
alive,
the
solution
will
turn
black
several
weeks
The
ammonium
iron(II)
sulphate
hexhydrate
and
ascorbic
were
sterilized
by
ultraviolet
radiation
for
30 min
and
mixed
the
media,
together
with
the
incubation
of
the
SRB
seeds.
Three
experiments
were
performed
under
the
same
conditions.
2.3.
Electrochemical
measurements
All
electrochemical
measurements
were
performed
on a CHI
604D
in
trode,
working,
Potentiodynamic
by
KCl)
sured
100
amplitude.
open-circuit
impedance
electrochemical
station
(CH
instrument
Co.,
Shanghai,
China)
a
three-compartment
cell
at room
temperature.
The
copper
elec-
an Ag/AgCl
(3 M
KCl)
electrode,
and
a
Pt
wire
served
as
the
reference,
and
counter
electrodes,
respectively.
polarization
determinations
were
carried
out
scanning
the
potential
from
−0.4
to 0.1
V versus
Ag/AgCl
(3 M
at
a
scan
rate
of
1 mV
s−1. Each
impedance
spectrum
was
mea-
at
an
open-circuit
corrosion
potential
in the
frequency
range
kHz
to 10 mHz
under
excitation
of
a sinusoidal
wave
of 5 mV
Impedance
spectra
were
obtained
after
2 h, when
the
potentials
of
the
electrodes
had
become
steady.
The
spectra
were
fitted
using
ZsimpWin
software.
2.4.
Surface
analysis
Bare
and
coated
copper
samples
immersed
in SRB
culture
media
were
(FESEM)
(JSM-6700F,
gies
Microanalysis
position
For
coated
cultured
with
to
analyzed
by
field
emission
scanning
electron
microscopy
and
energy
dispersive
X-ray
spectrometry
(EDS).
FESEM
Philips
XL30)
was
used
to characterize
the
morpholo-
of
the
copper
sheets,
while
EDS
(OXFORD
INCA
Energy
X-ray
system)
was
used
to determine
the
chemical
com-
of
the
surfaces.
FESEM
and
EDS
analyses,
control
and
composite
coating
copper
samples
were
immersed
in a stationary
phase
SRB
media
for
6 h.
Afterwards,
they
were
immediately
rinsed
ultra-pure
water,
dried
under
an
N2atmosphere,
and
brought
the
laboratory
without
further
treatment.
2.5.
Fabrication
process
The
fabrication
procedure
is
shown
in Scheme
1.
The
SAMs
were
formed
of
ples
by
immersing
the
pretreated
copper
in an MUA
solution
ethanol
(5 mM)
overnight.
After
modification,
the
copper
sam-
were
removed
from
the
solution,
rinsed
with
absolute
ethanol
Scheme
1.
Fabrication
process
including
two
stages:
(a)
self-assembled
monolayer
and
(b)
the
sol–gel
process.

Page 4

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/ Applied
Surface
Science
257 (2011) 10529–
10534
10531
0.20.10.0-0.1-0.2-0.3
E/V vs. Ag/AgCl (3M KCl)
-0.4
-9
-8
-7
-6
-5
-4
-3
-2
d
c
b
a
logi (Acm-2)
Fig.
coated
1.
Polarization
curves
for
(a)
bare,
(b)
MUA,
(c)
CS/MUA,
and
(d)
MBT-CS/MUA
copper
electrodes
in 3.5%
NaCl
solution
at
1 mV
s−1from
−0.4
to 0.1
V.
to remove
carboxyl
surface
[16].
solution.
to yield
copper
naturally
the–NH2group
and
that
excess
reactants,
and
dried
under
a stream
of
N2. The
end
groups
of
MUA
formed
a
negatively
charged
copper
through
the
formation
of
MUA
self-assembled
monolayers
CS
(0.1
g)
was
dissolved
in 6 mL
8% (w/w)
acetic
acid
aqueous
MBT
was
then
dissolved
into
it under
vigorous
stirring
a 1.27%
(w/w)
MBT
doped
CS
solution.
The
MUA
modified
surface
was
dip-coated
into
the
MBT-CS
hydrogel,
and
then
dried
at room
temperature.
The
ionic
interaction
between
at
the
C-2
position
of CS’s
glucosamine
repeat
unit
the
–COOH
end
group
of
MUA
produced
a composite
coating
can
be
stable
in aggressive
solutions
[14].
3.
Results
and
discussion
3.1.
Potentiodynamic
polarization
measurements
The
potentiodynamic
CS/MUA,
of
an
reduction:
polarization
curves
for
bare,
MUA,
and
MBT-CS/MUA
coated
copper
in an
aqueous
solution
3.5%
NaCl
are
shown
in Fig.
1.
The
cathodic
corrosion
reaction
in
aerated
NaCl
solution
of
copper
is
attributed
to dissolved
oxygen
O2+ 2H2O +
The
chloride
However,
draw
In
[18], though
(a),
4e−→ 4OH−
(1)
kinetics
and
mechanism
of
anodic
corrosion
reaction
in
media
(Cl−< 1 M)
has
been
reviewed
by Kear
et
al.
[17].
at
least
three
cases
were
proposed,
so it is difficult
to
an
unambiguous
conclusion
about
the
detailed
reaction
steps.
this
study,
we
take
the
modified
process
described
by Sherif
et al.
it remains
under
debate.
In the
Tafel
region
of
Curve
the
electro-dissolution
of
copper
proceeds
as
follows:
Cu
↔ Cu++ e−
As
current
0.05
the
potential
its
(2)
the
potential
moves
towards
the
more
positive
direction,
the
density
shows
a monotonic
increase
until
a peak
value
at
V versus
Ag/AgCl
(3 M KCl)
is reached.
After
this
maximum,
current
density
rapidly
declines
to a limiting
value
with
further
increases.
This
is related
to the
CuCladscoverage
reaching
maximum:
Cu
+ Cl−↔ CuClads+
where
unable
ble
increases:
e−
(3)
CuCladsis an
insoluble
adsorbed
species
with
poor
adhesion,
to protect
the
copper
surface.
CuCladstransforms
to the
solu-
cuprous
chloride
complex
CuCl2−, and
the
current
density
again
CuClads+ Cl−↔
CuCl2−
(4)
This
causes
copper
to form
a porous
and
unstable
cuprous
oxide
film:
2CuCl2−+
For
rent
potential
that
and
process
dissolved
resulting
For
has
is
The
the
formation
polymeric
with
of
process
positive
The
from
2OH−↔
Cu2O +
H2O +
4Cl−
(5)
both
MUA
and
CS/MUA
covered
electrodes,
cathodic
cur-
densities
were
significantly
reduced
(Fig.
1b,
c).
The
corrosion
(Ecorr) shifted
towards
more
negative
values,
indicating
both
MUA
and
CS
acted
as
barriers
to the
diffusion
of
oxygen
water.
Thus,
cathodic
reaction
was
suppressed,
whereas
anodic
was
not
inhibited
in the
presence
of
the
layers.
Copper
was
from
the
surface
by
anodic
process
without
difficulty,
in a
lack
of
suppression
of
the
anodic
process.
MBT-CS/MUA
composite
coatings,
the
protective
behavior
a mixed
effect
(Fig.
1d).
Suppression
of
the
cathodic
process
also
attributed
to the
arrested
diffusion
of oxygen
and
water.
presence
of
MBT,
a group
of
mixed-type
inhibitors,
results
in
reduction
of
both
anodic
and
cathodic
current
densities.
The
of
an
adherent
water-insoluble
[Cu(I)-MBT]adscomplex
film
by the
surface
reaction
of
adsorbed
MBT
molecules
either
copper,
CuClads,
or
CuCl2−suppresses
the
dissolution
copper
from
the
substrate,
resulting
in inhibition
of
the
anodic
and
a
slight
shift
of
the
corrosion
potential
(Ecorr) to the
direction
[19].
protective
efficiencies
(PE)
(%)
of
the
coatings
are
calculated
the
equation:
?
corrand
PE(%)
=
1 −icorr
i0
corr
?
× 100%
where
by
coated
MUA,
97.70%,
corrosion
study,
amounts
surface,
i0
icorrdenote
the
corrosion
current
densities
obtained
Tafel
extrapolation
of
the
polarization
curves
of
uncoated
and
electrodes,
respectively.
The
calculated
values
of PE
for
CS/MUA,
and
MBT-CS/MUA
coatings
are
81.95%,
91.49%,
and
respectively.
Traditionally,
inhibitors
are
added
to
whole
environments
to minimize
corrosion
of
the
metal.
In this
we
achieved
high
protective
efficiency
using
much
smaller
of
inhibitors,
as
the
MBT
was
only
located
on the
copper
with
no
redundant
MBT
in the
bulk
solution.
3.2.
Electrochemical
impedance
spectra
Electrochemical
information
Fig.
and
NaCl
per
the
0.01
of
magnitude.
from
the
ear
angle
of
The
terized
frequency
influence
related
constant
developed,
per
composite
itive
impedance
spectra
(EIS)
provide
excellent
about
the
corrosion
prevention
of
the
coating
film.
2 compares
the
impedance
spectra
obtained
on bare,
MUA,
MBT-CS/MUA
composite
film-coated
copper
electrodes
in 3.5%
solution
after
2 h immersion.
The
composite
film
coated
cop-
showed
higher
impedance
at all
frequencies
compared
with
other
two
electrodes.
The
impedance
at the
lowest
frequency,
Hz,
which
may
relate
to the
corrosion
prevention
performance
the
coating
film
[20], was
higher
by
approximately
one
order
of
The
results
obtained
from
EIS
agree
with
those
obtained
potentiodynamic
polarization
measurements.
From
Fig.
2a,
impedance
diagram
of
bare
copper
in NaCl
solution
exhibits
lin-
dependence
in log|Z|
versus
log
f, with
a
slope
=
−1/2,
and
phase
of
45◦in the
medium
frequency
region.
This
is
characteristic
Warburg
impedance,
indicating
a diffusion
effect
[21].
impedance
spectrum
of
SAMs
coated
copper
was
charac-
by
two
time
constants:
high
frequency
(hf)
and
medium
(mf)
(Fig.
2b).
The
hf
time
constant
was
attributed
to the
of
SAM
on
the
copper
surface,
whereas
the
mf
one
was
to the
corrosion
process.
The
appearance
of
the
mf
time
after
only
2 h immersion
proves
that
defects
in the
SAM
and
the
aggressive
solution
quickly
reached
the
cop-
surface.
EIS
tests
performed
on
the
copper
electrode
treated
by
coating
are
characterized
by
a high-frequency
capac-
response,
which
can
be
assigned
to the
capacitance
of the

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10532
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/ Applied
Surface
Science
257 (2011) 10529–
10534
6543210-1-2
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
log(Z/Ohm)
log(f/Hz)
a
c
b
654321
log(f/Hz)
0 -1 -2
0
10
20
30
40
50
60
70
80
-Phase angle/deg.
a
b
c
Fig.
2.
Bode
plots
obtained
from
(a)
bare,
(b)
MUA,
and
(c)
MBT-CS/MUA
coated
copper
electrodes
after
2 h immersion
in 3.5%
NaCl
solution.
Fig.
tra
between
3.
The
equivalent
circuit
used
for
numerical
simulations
of
the
EIS
spec-
obtained
from
the
MBT-CS/MUA
coated
copper
electrode
and
the
correlation
the
model’s
elements
and
their
physical
representatives.
composite
performed
circuit
The
electrolyte
the
of
Qdland
layer
the
substitute
stant
composition
face
the
exists
trical
coating
(Fig.
2c).
A detailed
interpretation
of Fig.
2c
was
by fitting
the
experimental
plots
using
the
equivalent
shown
in Fig.
3.
symbol
Rsolrepresents
the
solution
resistance
of
the
bulk
between
the
reference
and
working
electrodes,
Ccoatis
capacitance
of
the
composite
coating,
Rpois the
pore
resistance
the
composite
coating,
Rctis
the
charge
transfer
resistance,
and
Qinterare
the
constant
phase
elements
(CPEs).
The
double-
does
not
behave
as
an
ideal
pure
capacitor
in the
presence
of
dispersing
effect,
so a constant
phase
element
(Qdl) is
used
as
for
the
capacitor.
As
far
as
Qinteris concerned,
the
con-
phase
element
may
be caused
by the
special
property
of
the
of
the
coating.
As
previously
depicted,
there
is an
inter-
between
the
negative
charge
arranged
in the
SAM
layer
and
positive
charge
contained
in the
CS hydrogel.
Accordingly,
there
another
interface
capacitance-like
element
reflected
by
elec-
signals.
Similarly,
this
interface
does
not
behave
as
an
ideal
capacitor,
of
is
respectively
so a constant
phase
element
is
used
instead.
The
value
CPE
is a function
of
the
angular
frequency,
ω,
and
whose
phase
independent
of
the
frequency.
Its
admittance
and
impedance
are
expressed
as
YCPE= Y0(jω)n
ZCPE= 1/Y0(jω)−n
where
and
The
itored
from
are
as
cell
of
a lower
subtle
structural
ing
was
ing
upon
other
and
the
Y0is
the
magnitude
of
the
CPE,
ω is the
angular
frequency,
n is
the
exponential
term
of
the
CPE.
evolution
in the
protective
action
of
the
coating
was
mon-
by
EIS
measurements.
The
electronic
parameters
obtained
fitting
the
experimental
EIS
using
the
above
equivalent
circuit
listed
in Table
1.
The
Rsolis not
influenced
by
electrode
processes
its
value
depends
on
the
conductivity
of
testing
medium
and
the
geometry.
The
capacitance
of
the
coating
(Ccoat) is an indicator
protective
performance,
i.e.,
the
barrier
properties
of the
coating:
capacitance
reveals
a more
protective
coating,
and
the
more
change
in Ccoatover
the
entire
exposure
may
reflect
greater
integrity
of
the
film
[6]. The
Ccoatof
the
composite
coat-
changed
little
over
the
experiment
time.
The
maximum
value
2.9
?F cm−2and
the
minimum
value
was
2.0
?F cm−2, indicat-
this
coating
was
effective
in maintaining
its
barrier
properties
exposure
to chloride
ions
and
dissolved
O2. Generally,
all
the
elements
smoothly
changed,
indicating
the
barrier
properties
stability
of
the
composite
coating
during
immersion.
Some
of
4 h data
were
ignored
due
to bad
fitting
results.
3.3.
SEM
characterization
and
EDS
analysis
We
also
studied
the
corrosion
behavior
of
uncoated
and
coated
copper
of
hydrogen
The
sulphides
is
ions
samples
in the
SRB
culture.
The
enhancement
of corrosion
copper
and
copper
alloys
in the
presence
of
SRB
is mainly
due
to
sulphide
produced
by
the
bacterial
reduction
of sulphate.
sulphide
ions
can
get
incorporated
into
the
passive
film
as
metal
and
deteriorate
passivity
[22].
The
SRB
culture
medium
a highly
corrosive
environment
containing
1.2–1.8
mM
sulphide
after
the
SRB’s
exponential
growth
phase
stage
[23,24]. The
Table
Parameters
1
obtained
by
fitting
the
impedance
spectra
of
the
copper
electrode
coated
by MBT-CS/MUA
composite
film
with
the
equivalent
circuit
shown
in Fig.
3.
Time
(h)

Rsol
Ccoat
Qinter
Rpo
Qdl
Rct
? cm2
?F cm−2
Y0(?−1cm−2sn)
n
? cm2
Y0(?−1cm−2sn)
n
? cm2
2
4
6
8
5.3
5.6
5.7
5.7
5.8
5.8
2.5
2.9
2.3
2.2
2.1
2.0
2.0
–
1.3 × 10−5
1.8 × 10−4
1.7 × 10−4
8.8 × 10−6
× 10−5
0.66
–
0.70
0.48
0.49
0.76

2.5 × 103
–
3.5 × 103
4.6 × 104
4.5 × 104
4.5 × 103
1.8 × 10−4
1.2 × 10−4
1.8 × 10−4
1.1 × 10−5
9.6 × 10−6
1.7 × 10−4
0.47
0.27
0.47
0.73
0.75
0.50

3.8
–
4.7
4.0
4.3
4.2
× 104

× 104
× 103
10
12
× 103
× 104

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/ Applied
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Science
257 (2011) 10529–
10534
10533
Fig.
of
bare
after
4.
Optical
photographs
showing
(A)
comparison
of
control
tube
1,
containing
the
exponential
phase
SRB
culture,
tube
2,
containing
the
same
SRB
culture
with
the
addition
CS (3.33
?g/mL),
and
tube
3,
containing
the
same
SRB
culture
with
the
addition
of
CS
(3.33
?g/mL)
+ MBT
(2.78
?g/mL)
after
incubation
for
two
weeks;
(B)
corroded
(a)
copper,
(b)
CS,
(c)
MUA,
(d)
MUA/CS,
and
(e)
MBT-CS/MUA
covered
copper
sheets
taken
out
from
the
SRB
culture
after
6 h immersion
immediately
and
exposed
to
air
10
min.
pH
dominant
of
this
The
ing
reactions
of
4th–16th
d SRB
culture
range
from
7.95–7.80.
Therefore,
the
form
of
the
sulphur
element
is HS−, based
on
calculations
the
acid
dissociation
of
H2S (Ka1= 9.1
× 10−8, Ka2= 1.1
× 10−12) at
condition.
anodic
reaction
mechanism
of
copper
in sulphide
contain-
chloride
medium
can
be
described
by
the
following
series
of
[25]:
Cu
+ HS−→
Cu(HS−)ads→ Cu(HS)
Cu(HS)
Cu(HS−)ads
(6)
+ e−
(7)
→ Cu++ HS−
(8)
2Cu++ HS−+
Cu2O could
Eq.
The
by
black
composite
darkened
did
the
H2S corrosion.
conditions,
OH−→ Cu2S + H2O
(9)
also
be
formed
as
a
parallel
reaction,
as
shown
by
(5).
optical
photograph,
Fig.
4B,
shows
that
the
samples
coated
CS
were
all
well-protected
and
their
surface
did
not
turn
compared
with
the
bare
and
SAMs-only-coated
copper.
The
coating
has
the
best
appearance
because
the
surface
the
least.
The
CS
gel
without
inhibitor
and
the
SAM
also
not
seem
significantly
affected
(Fig.
4B).
This
illustrates
that
sole
CS
gel
acts
as
a physical
barrier
to provide
protection
from
However,
after
only
10
min
exposure
at
ambient
the
gel
began
to blister
and
crack,
and
then
naturally
Fig.
2000×
5.
FESEM
images
of
bare
copper
at a magnification
of
(A)
2000× and
(B)
20,000×, and
MBT-CS/MUA
composite
coating
covered
copper
at a
magnification
of
about
(C)
and
(D)
20,000× after
6 h immersion
in SRB
culture
media.

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10534
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/ Applied
Surface
Science
257 (2011) 10529–
10534
Fig.
covered
6. EDS
analysis
for
(A)
bare
copper
and
(B)
MBT-CS/MUA
composite
coating
copper
samples
after
6 h immersion
in SRB
culture
media.
peeled
Through
the
Fig.
SRB
sulphide,
and
SRB
black
ever,
a
[26].
To
rial
media.
were
of
tions,
EDS
and
can
for
ing
the
off
due
to poor
affinity
with
the
inorganic
metal
substrate.
the
damaged
part
of
the
coating,
we
can
directly
see
that
underlying
copper
was
well-protected.
5 shows
FESEM
images
of
the
copper
coupons
exposed
to the
culture
media
for
6 h.
Under
the
synergistic
actions
of
hydrogen
chloride
and
hydroxyl
ions,
corrosion
reactions
occurred
the
bare
copper
surface
became
rough
and
non-uniform.
The
bacteria
began
to settle
on
its
surface,
which
appeared
as
small
shadows
reflecting
the
bacteria
shape
under
FESEM.
How-
we
could
not
find
any
SRB
on
the
composite
film.
CS
has
bacteriostatic
activity.
MBT
may
also
be
an
antibacterial
agent
As
a result,
SRB
could
not
grow,
or
even
settle
on
the
surface.
further
make
sure
whether
both
participated
in the
antibacte-
function,
CS
and
CS
+ MBT
were
dissolved
into
the
SRB
culture
From
Fig.
4A,
control
tube
1 turned
black,
whereas
the
others
clear.
No
SRB
survived
after
two
weeks
incubation,
as
a result
CS’s
obvious
bacteriostatic
activity.
Based
on
these
considera-
microbiologically
influenced
corrosion
was
suppressed.
analysis
of
the
corroded
bare
copper
reveals
peaks
for
Cu,
S,
O that
are
in
good
agreement
with
our
previous
discussion,
as
be
seen
in Fig.
6A.
The
coated
electrode
shows
no
peaks
even
Cu
indicating
total
coverage
of
the
substrate
by
the
intact
coat-
(Fig.
6B).
Active
sites
on
the
surface
of
copper
were
occupied
by
thiol
group
of
the
MUA
and/or
MBT
organic
inhibitor,
together
with
per
coating.
the
coating
acting
as
a
physical
barrier,
the
dissolution
of
cop-
was
blocked
and
no
copper
ion
released
out
of
the
composite
The
attack
of
HS−was
prevented.
4.
Conclusions
An MBT
per,
Potentiodynamic
had
EIS
tion
MBT-CS/MUA
solution.
and
posite
kill
the
further
study.
doped
CS
composite
was
successfully
coated
onto
cop-
thereby
improving
its
corrosion
resistance
and
durability.
polarization
reveals
that
the
composite
coating
a
mixed
inhibiting
effect
on
both
cathodic
and
anodic
reactions.
spectra
indicate
that
the
composite
coating
provided
protec-
within
the
experimental
time.
Copper
species
coated
with
were
also
well
protected
from
sulphide
ions
in NaCl
The
MBT-CS/MUA
coating
presented
both
anticorrosion
antibacterial
features,
as
SRB
were
contact-killed
by
the
com-
coating.
Even
dissolved
CS
polycationic
macromolecules
can
SRB
in solution.
Although
the
corrosion
resistance
property
of
composite
coating
was
improved
in this
work
to some
extent,
increases
in the
efficiency
of
the
coating
requires
further
Acknowledgements
This
work
was
supported
by the
Chinese
Academy
of
Sciences
(grant
Foundation
no.
KZCX2-YW-205-03)
and
the
National
Natural
Science
of
China
(grant
no.
41076047).
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