Anderson_et_al-2016-Advanced_Materials_Interfaces

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© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim (1 of 8) 1500632wileyonlinelibrary.com
Robust Nanostructured Silver and Copper Fabrics with
Localized Surface Plasmon Resonance Property for Effective
Visible Light Induced Reductive Catalysis
Samuel R. Anderson, Mahsa Mohammadtaheri, Dipesh Kumar, Anthony P. O’Mullane,
Matthew R. Field, Rajesh Ramanathan,* and Vipul Bansal*
S. R. Anderson, M. Mohammadtaheri, D. Kumar,
Dr. R. Ramanathan, Prof. V. Bansal
Ian Potter NanoBioSensing Facility
NanoBiotechnology Research Laboratory (NBRL)
School of Science
RMIT University
GPO Box 2476V
Melbourne, VIC 3001, Australia
E-mail: rajesh.ramanathan@rmit.edu.au; vipul.bansal@rmit.edu.au
Prof. A. P. O’Mullane
School of Chemistry
Physics and Mechanical Engineering
Queensland University of Technology (QUT)
GPO Box 2434
Brisbane, QLD 4001, Australia
Dr. M. R. Field
RMIT Microscopy and Microanalysis Facility (RMMF)
RMIT University
GPO Box 2476V
Melbourne, VIC 3001, Australia
DOI: 10.1002/admi.201500632
strong influence of particle size and the
availability of active sites on the catalytic
activity, it is unsurprising that metal nano-
particles of different morphologies have
been fabricated and investigated.[1d–f,j,k,2]
Although Pt and Pd are highly active cata-
lysts,[2]
metal nanoparticles based on Ag
and Cu have a significant advantage over
their more noble counterparts in the con-
text of cost and in that they demonstrate
intense absorbance properties in the visible
region due to LSPR.[3]
This, in principle,
makes Ag and Cu nanoparticles desirable
candidates for promoting catalytic reac-
tions, especially under photoillumination
conditions.[1k,4]
However, difficulties in the
recovery of the nanocatalysts after the com-
pletion of the reaction typically limit their
practical applicability in catalytic applica-
tions.[5]
This limitation can be overcome by
immobilizing metal nanoparticles on solid
supports such as a metal oxide.[1,6]
An alter-
native strategy is to use a templating approach, wherein metal
nanoparticles are deposited directly on a template, for instance
through loading nanoparticles on different forms of papers,[5]
or directly depositing them on diatoms frustules.[7]
Such metal-
loaded substrates exhibiting hierarchical structuring on the
micrometer and nanometer scales, in principle, will not only
contain a high number of catalytically active sites to promote a
catalytic reaction,[5,7] but also eliminate the need for expensive
lithography techniques while simultaneously achieving facile
extraction of the catalyst postreaction.[7] Therefore, the use of
templates offers a unique way to fabricate materials that can be
directly assembled on highly ordered 3D architectures leading to
macro-, micro-, and mesoporous assemblies.
In the context of templating, fabrics have gained special
attention due to their use in everyday life, flexibility, high
maneuver-ability, well-established high-throughput manufac-
turing processes, and potential economic viability.[8] Addition-
ally fabrics have beneficial properties such as high hierarchical
ordering, porosity, absorbency, and wettability.[9] Our group and
others have already shown the importance of using cotton fabrics
as templates to grow semiconducting materials for gas sensing,
optoelectronics, self-cleaning, oil/water separation, and antimi-
crobial applications.[8,9] Moreover, high-throughput processes for
manufacturing a range of cotton fabric-based materials already
Inspired by high porosity, absorbency, wettability, and hierarchical ordering on the
micrometer and nanometer scale of cotton fabrics, a facile strategy is developed
to coat visible light active metal nanostructures of copper and silver on cotton
fabric substrates. The fabrication of nanostructured Ag and Cu onto interwoven
threads of a cotton fabric by electroless deposition creates metal nanostructures
that show a localized surface plasmon resonance (LSPR) effect. The micro/
nanoscale hierarchical ordering of the cotton fabrics allows access to catalytically
active sites to participate in heterogeneous catalysis with high efficiency. The
ability of metals to absorb visible light through LSPR further enhances the cata-
lytic reaction rates under photoexcitation conditions. Understanding the modes
of electron transfer during visible light illumination in Ag@Cotton and Cu@
Cotton through electrochemical measurements provides mechanistic evidence
on the influence of light in promoting electron transfer during heterogeneous
catalysis for the first time. The outcomes presented in this work will be helpful in
designing new multifunctional fabrics with the ability to absorb visible light and
thereby enhance light-activated catalytic processes.
1. Introduction
The use of metal nanoparticles based on platinum, palladium,
gold, silver, and copper as catalysts is well known.[1]
Given the
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© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheimwileyonlinelibrary.com1500632 (2 of 8)
exist,[8] allowing the facile integration of new functionalities in
these unique substrates in an economically viable manner. Cur-
rent strategies to create functional fabrics, especially metal oxide
coated fabrics, involve the use of sputtering/sol gel processes that
are time consuming and may require high temperatures.[8a,b,10]
Similarly, metal-coated fabrics previously fabricated through the
use of a layer by layer process, sonochemical coating, or through
the synthesis of the nanoparticles first before incorporating
them on the fabrics face similar challenges.[12] These limitations
associated with postsynthesis deposition of nanoparticles onto
fabrics could be potentially overcome through the use of a facile
electroless deposition strategy to deposit visible light active metal
nanoparticles on cotton fabrics.[11] Further, the applicability of the
metal-coated fabrics containing silver and copper (in oxide form)
has largely been limited to antibacterial applications as silver and
copper are both well-known for their antibacterial activity. How-
ever, to the authors’ best knowledge, the use of silver and copper
fabrics for catalysis applications has not been investigated. Addi-
tionally, the influence of light on enhancing electron-transfer
processes during catalytic reactions is not well-understood in
metal systems.
In this work, we developed a facile, robust, and time efficient
strategy to construct nanostructures of photoactive silver and
copper on cotton fabric surfaces that are amenable for large-
scale fabrication. The strategy employs a simple electroless tech-
nique to deposit silver and copper nanostructures on individual
cotton threads embedded within the 3D matrix of a cotton
fabric. The light driven catalytic properties of these metal-coated
fabrics were investigated using a well-established reductive cat-
alytic reaction involving ferricyanide and thiosulfate ions in an
aqueous solution. The mechanistic understanding of the under-
lying electron-transfer processes at the solid–solution interface
probed using electrochemical analyses provided vital clues on
the influence of visible light on the transfer of electrons from
the solution-based species to the catalyst surface and from the
catalyst to the solution species during the reaction.
2. Results and Discussion
2.1. Fabrication of Cu@Cotton and Ag@Cotton
The electroless deposition of copper and silver on the surface
of cotton fabrics proceeds via a three-step “sensitization-seeding-
deposition” process (Scheme 1). Step 1 involves sensitizing the
cotton fabric using an acidic solution of tin chloride wherein
the Sn2+ ions bind to the surface of individual cotton fibers. The
sensitized fabric is then immersed in a palladium salt solution
allowing the formation of Pd0 nuclei (Step 2). The spontaneous
formation of Pd nuclei on the surface of the fabric proceeds
via the formation of Sn4+ during the reduction of Pd2+ to Pd0.
The favorable difference in the standard reduction potentials
of Pd2+/0 (+0.99 V vs standard hydrogen electrode (SHE)) and
Sn4+/2+ (+0.15 V vs SHE) allows the reaction to proceed sponta-
neously. Although the standard reduction potentials of copper
(Cu2+/Cu0 +0.34 V vs SHE) and silver (Ag+/Ag0 +0.799 V vs
SHE) will in principle allow the deposition of these metals
directly on the sensitized (Sn4+) cotton fabric, deposition of Cu
and Ag on the fabric is significantly slower in the absence of
palladium.[11] The Pd0 layer formed through the spontaneous
reaction between Sn4+ and Pd2+ acts as a catalytic center to
increase the reaction rate for the deposition of photoactive
silver or copper nanostructures on the sensitized cotton fabric
surface (step 3). The deposition of nanostructured silver occurs
through the reduction of a diaminesilver (I) complex;[11,13]
while
the deposition of nanostructured copper proceeds through the
reduction of copper sulfate using formaldehyde under alkaline
conditions.[11,14]
This strategy therefore eliminates the need for
nonaqueous solvents or postsynthesis binding of nanoparticles
to the substrate/template through functionalization or the need
for high reaction temperatures. Equal amount of metal deposi-
tion was ensured for both Cu and Ag by controlling the time
taken for the electroless plating reaction. A total of 12 mg of Cu
and Ag was deposited on the 2 × 2 cm2
cotton fabric surface.
2.2. Characterization of Cu@Cotton and Ag@Cotton
Figure 1 shows the representative SEM images of the fabric
surface where deposition of Cu and Ag through an electroless
process results in the formation of nanostructured quasispher-
ical Cu (Figure 1a1–a3) and Ag (Figure 1b1–b3) particles coated
on individual threads of the cotton fabric. The deposition of
the metal was also clearly visible to the naked eye where a red-
dish color was observed in the case of the Cu@Cotton while a
brownish black color was observed in the case of the Ag@Cotton
(Figure S1, Supporting Information). These colors correspond
primarily to the collective LSPR absorption of sub-100 nm
CuNPs[4,15] and AgNPs[16] assembled on the surface of the
cotton fabric (Figure 1a3,b3). The EDX spectra of Cu@Cotton
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Scheme 1. Schematic diagram representing the three facile steps involved during the fabrication of Cu@Cotton and Ag@Cotton fabrics. Step 1 involves
the “Sensitization” of the fabric with Sn2+. Step 2 involves the formation of Pd seeds that act as “Nucleation” sites. Step 3 involves electroless “Growth”
of metallic copper and silver nanoparticles on the surface of the cotton fabric.

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and Ag@Cotton show characteristic energy lines of C Kα
(0.277 keV) and O Kα (0.524 keV), which arise predominately
from the underlying cotton fabric, while the Cu@Cotton shows
characteristic Cu Lα peaks at 0.929 keV (Figure 1a4) and the
Ag@Cotton shows characteristic Ag Lα/Lβ peaks at 3/3.351 keV
(Figure 1b4). The EDX elemental mapping of Cu and Ag indi-
cated that the nanoparticles were distributed on the cotton
surface uniformly (Figure 1a5,b5). The crystalline nature of
metal nanostructures was determined using XRD (Figure S2,
Supporting Information), while the surface chemical com-
position of the metal-coated fabric was determined by XPS
(Figures S3 and S4, Supporting Information). The analyses
confirmed that the deposited metal nanostructures were indeed
pristine metals. However for Cu@Cotton, additional Bragg
reflections corresponding to cupric oxide (CuO) were observed
due to the high propensity of copper to oxidize in air.[15]
The
existence of an oxide layer on Cu@Cotton fabric was also
observed in the XPS experiments. The Cu 2p core level obtained
from Cu@Cotton shows two characteristic 2p3/2 and 2p1/2 split-
ting components (spin–orbit splitting ≈19.7 eV). The Cu 2p
core level (Figure S3a, Supporting Information) could be decon-
voluted into two components at binding energies (BE) of ≈932.8
and 934.7 eV. These correspond to copper in the zerovalent
(Cu0) and Cu2+ oxidation states, respectively.[15,17] The presence
of signatures corresponding to shake-up satellites at ≈943.5 and
964 eV further supports formation of CuO on the surface of
Cu@Cotton. The shake-up satellite peaks are seen due to nona-
diabatic relaxation of the electron cloud upon photoionization
wherein the energy from the X-ray source promotes a valence
electron to an unoccupied state. This primarily gives rise to
shake up transition or extra peaks in the XPS spectrum.[1a] For
Cu, shake-up satellites are only observed in the case when Cu is
present in the +2 oxidation state.[15] This suggests that the peaks
obtained for Cu@Cotton fabric are indeed from CuO. Further,
given that the binding energies of Cu+ and Cu0 are similar, the O
1s spectrum was also analyzed to confirm the absence of Cu2O
(Figure S3b, Supporting Information). The strong signature
at ≈531.2 eV with a minor component at 533.6 eV further
confirms the absence of Cu+
species and that the copper in
Cu@Cotton is present in the Cu0
and Cu2+
oxidation states.[17]
Similarly, the core level Ag 3d and O 1s spectra from Ag@
Cotton were also deconvoluted. The Ag 3d core level shows a
single component at ≈367.9 eV with two characteristic 3d5/2
and 3d3/2 splitting components (spin–orbit splitting ≈6 eV),
which correspond to Ag in the zerovalent oxidation state
(Figure S4a, Supporting Information). The BEs for the O 1s
spectra were slightly higher than that observed for copper as
the O 1s signature in the case of Ag is predominately from the
underlying cotton fabric (Figure S4b, Supporting Information).
In both cases, although Pd0
was used as a seed layer for the
deposition of metal during electroless deposition, no signatures
corresponding to Pd 3d was observed in the XPS, most likely
due to the small quantities of Pd used during the synthesis
(Figure 3c and Figure 4c).
The diffuse reflectance UV–vis spectrum (Figure S5, Sup-
porting Information) obtained from Cu@Cotton shows broad
absorption peaks at ≈500–600 nm (Figure S5a, Supporting
Information) and that from Ag@Cotton at ≈400–450 nm
(Figure S5b, Supporting Information). These SPR features are
typical for copper[4,15] and silver nanoparticles.[16] The presence
of characteristic SPR features attest to the nanodimensions of
Cu and Ag nanoparticles with broad particle size distribution
in the respective samples, and suggests that Cu@Cotton and
Ag@Cotton fabrics are likely to show LSPR effect when illumi-
nated with visible light.
2.3. Heterogeneous Catalysis Reaction
To be an ideal catalyst, nanostructures should exhibit high cata-
lytic activity through the exposure of catalytically active sites,
maintain excellent stability, recyclability, and operational sim-
plicity.[5,18] In addition, the recent discovery that the conduction
band electrons of Au, Ag, and Cu nanoparticles can gain visible
light energy through the LSPR effect to produce energetic “hot”
electrons facilitating the catalytic reaction process is of significant
interest.[4,19] The high porosity and hierarchical ordering on
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Figure 1. a1–a3) SEM images of Cu@Cotton, a4) EDX spectrum obtained from scanning area shown in a1, and a5) layered map image obtained from
EDX containing element mapping of Cu and O. b1–b3) SEM images of Ag@Cotton, b4) EDX spectrum obtained from scanning area shown in b1, and
b5) layered map image obtained from EDX containing element mapping of Ag and O.

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the micrometer and nanometer scale of cotton fabrics in com-
parison to metal foils should in principle not only expose more
catalytically active sites to promote the reaction to completion,
but the LSPR effect should also further enhance a catalytic reac-
tion. Given that silver and copper nanoparticles show a LSPR
effect, we explored the Cu@Cotton and Ag@Cotton fabrics for
the reductive conversion of ferricyanide to ferrocyanide ions in
the presence of excess thiosulfate ions, which was carried out
in the presence and absence of visible light illumination. This
pseudo-first order reaction (as the reaction occurs in the pres-
ence of excess thiosulfate ions) can be easily monitored using
UV–vis spectroscopy by analyzing the decrease in the absorp-
tion maxima of ferricyanide ions at ≈ 420 nm. Both Cu@
Cotton and Ag@Cotton catalyze the reduction of ferricyanide
to ferrocyanide under dark and visible light illumination, albeit
with different efficiencies. It was immediately clear that Cu is
inherently a better catalyst than Ag given that under dark con-
ditions, the reaction proceeds to completion within 5 min in
the presence of Cu@Cotton, in contrast to 45 min for Ag@
Cotton (Figure 2 and S6, Supporting Information). The reaction
kinetics were determined by plotting ln(At/A0) versus time and
analyzing the slope of the linear part of the graph, where At is
the intensity of the absorbance peak at time t while A0 is the
peak intensity at time zero. Under dark conditions, the reaction
rate obtained for Cu@Cotton is 1.11 min−1 (Figure 2a), which is
an order of magnitude better than that of Ag@Cotton wherein
the reaction rate was 0.11 min−1 (Figure 2b). When the same
reaction was carried out under the stimulus of visible light, the
time taken for the reaction to reach completion is faster for
both Cu@Cotton (Figure 2a) and Ag@Cotton (Figure 2b), albeit
with different efficiencies (Figure S7, Supporting Information).
The rate of reaction for the Cu@Cotton was enhanced from
1.11 min−1 to 1.60 min−1, taking 40% less time for the reaction
to proceed to completion. In contrast, Ag@Cotton showed a
33.33% decrease in the time taken for the reaction to proceed
to completion, while showing an enhanced reaction rate of
0.17 min−1. This enhancement can be attributed to the LSPR
effect, which is typical for these types of metal nanoparticles.
It has been suggested that during light excitation, the conduc-
tion band electrons gain energy from visible light through
LSPR resulting in high-energy electrons
at the surface of the metal.[3]
The reso-
nance of the conduction electrons with the
electromagnetic field of the incident light
results in a significant enhancement of the
local electromagnetic fields near the sur-
face of the metal nanoparticles.[1k,3,4]
This
may result in an improved rate of reaction
during catalysis. Notably, typical reaction
rates for coinage metals for this particular
reaction are approximately 10−3
min−1
while
using a 3 mL reaction volume.[1k,7c,18]
In
contrast, the reaction rates observed in the
current study involving a 30 mL reaction
volume are at least three orders of magni-
tude better. It may be expected that if reac-
tions are performed in smaller volumes, the
reaction rates will be further improved sig-
nificantly. However, it is notable that when
we originally attempted to perform catalytic
reactions in 3 mL reaction volumes, most of
the reactions took less than 1 minute to com-
plete (Cu@Cotton: ≤1 min both in light and
dark; Ag@Cotton: 2 min in light and 3 min
in dark). This was due to the high catalytic
efficiency of our materials, which made it
difficult to study the influence of light on
the catalytic performance of metal fabrics in
3 mL reaction volumes. Therefore the cur-
rent studies were focused on 30 mL reac-
tion volumes. Control experiments were also
carried out using 12 mg of each Cu and Ag
metal foil, which is the same as the loading
of these metals on the cotton fabric, as well
as a 2 × 2 cm2 Cu and Ag foil surface, which
is the same size dimensions as of the cotton
fabric used to decorate Cu and Ag nano-
particles. The time taken for 98% degrada-
tion of ferricyanide for both cases was higher
a b
c d
0 10 20 30 40 50
-5
-4
-3
-2
-1
0
Ln(At
/A0
)
Time /min
Dark
Light
0 1 2 3 4 5
-5
-4
-3
-2
-1
0
Ln(At/A0)
Time /min
Dark
Light
0 5 10 15
1
2
3
4
5
Rateofreaction/min-1
No. of cycles
0 5 10 15
0.0
0.5
1.0
1.5
2.0
Rateofreaction/min-1
No. of cycles
3 6 9 12 15
0
20
40
60
80
100
Conversion/%
No. of cycles
3 6 9 12 15
0
20
40
60
80
100
Conversion/%
No of cycles
Figure 2. Plot of Ln(At/A0) versus time for a) Copper@Cotton and b) Silver@Cotton in the
presence and absence of visible light. Plot of the rate constants for 15 consecutive cycles
using the same c) Copper@Cotton and d) Silver@Cotton. The inset shows the corresponding
catalytic conversion efficiency.

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than that obtained for Cu@Cotton and Ag@Cotton (Figure S8,
Supporting Information). A summary of the reaction rates and
reaction time for all the samples are outlined in Table 1. For
12 mg of foil, the reaction proceeds to completion only after
100 min for both Cu and Ag, in contrast to Cu@Cotton and
Ag@Cotton, which takes 5 and 45 min, respectively. Even with
a 2 × 2 cm2
Cu (359.2 mg) or Ag foil (430.3 mg), the reaction
rates and time required for reaction completion significantly
underperformed over those obtained for Cu@Cotton and Ag@
Cotton. Further, control experiments in the absence of the cata-
lyst and in the presence of cotton fabric (without metals) were
also carried out, which showed insignificant (3%) conversion of
ferricyanide to ferrocyanide after 100 min. This suggests that
depositing Cu or Ag on individual threads of the hierarchically
ordered cotton fabrics results in the exposure of a large number
of catalytically active sites that remarkably enhances the rate of
catalytic reactions.
The metal-loaded fabric surface was also characterized post-
catalysis. While SEM revealed no obvious change in the mor-
phology of the nanocopper and silver (Figure S9, Supporting
Information); XRD (Figure S10, Supporting Information);
and EDX (Figure S11, Supporting Information) suggested
the formation of a CuO layer on the surface of Cu@Cotton
(Figure S10a and S11a, Supporting Information), with no sig-
natures of any oxide on the surface of Ag@Cotton (Figure S10b
and S11b, Supporting Information).
The reusability of the catalyst was also evaluated by
employing the Cu@Cotton and Ag@Cotton fabrics for 15 con-
secutive catalytic reactions (Figure 2c,d). The rate constant and
catalytic efficiency for the Ag@Cotton fabric displayed a higher
degree of stability and reusability in comparison to Cu@Cotton
fabric wherein the rate constant and catalytic efficiency started
to reduce after the sixth cycle. This is most likely due to the pro-
pensity of copper to oxidise[15] during catalysis, which may lead
to the reduction of the overall catalytic efficiency during the
reusability test. Atomic absorption spectroscopy further sug-
gested higher leaching of copper from the Cu@Cotton fabric
than silver from the Ag@Cotton fabric (Figure S12, Supporting
Information).
2.4. Mechanism of Electron Transfer during LSPR-Induced
Reductive Photocatalysis
To gain information about the underlying electron-transfer
processes at the surface of the metal-coated fabrics during
catalysis, open circuit potential (OCP) versus
time experiments were carried out.[20] OCP
provides important information about charge
accumulation/dissipation processes at the
solid–solution interface.[18] The OCP experi-
ments were carried out under conditions sim-
ilar to that of the catalysis reaction (Figure 3),
wherein a steady state potential was
obtained within the first 200 s in 1 × 10−3 M
[Fe(CN)6]3− solution. The introduction of
S2O3
2− ions at this point (marked by an arrow
in Figure 3a–d) starts the reduction of ferri-
cyanide to ferrocyanide. The decrease in the
OCP on S2O3
2− injection in all the cases (black curves, Figure 3)
suggests that there is either an increase in the negative
charge or decrease in the positive charge on the surface of the
catalyst.[20d] In the current study, the former is more favoured
based on control experiments in the presence of S2O3
2− ions
only, which has a significant lower OCP value (red curves,
Figure 3) in comparison to the experiments involving both
[Fe(CN)6]3−
and S2O3
2−
ions. The comparison of the OCP versus
time data between copper and silver shows that the accumulation
of negative charge on the copper is considerably higher than that
of the silver under catalytic conditions, i.e., in the presence of
both reactants. This difference in the injection of negative charge
at the surface is expected to have implications on the catalytic
activity of Cu@Cotton and Ag@Cotton fabrics. Interestingly,
when the samples are illuminated with visible light this process
under catalytic conditions (black lines) remains unperturbed.
Furthermore, electrochemical impedance spectroscopy (EIS)
was also carried out to probe the ability of electrons to be trans-
ferred to the [Fe(CN)6]3−
ions at the catalyst surface.[18]
EIS pro-
vides information on the resistance to charge transfer at the
solid–liquid interface, which can influence the catalysis reac-
tion. Figure 4 shows the Nyquist plots that were obtained after
running the experiments at OCP. The width of the semicircle
component allows determination of the resistance to charge
transfer during the transfer of electrons to the [Fe(CN)6]3−
ions
from the catalyst surface.[18,21]
It is clear that light has a more
pronounced influence on the resistance to charge transfer in the
case of copper (Figure 4a) compared to that of silver (Figure 4b).
It was interesting to observe a semicircle component in the
case of copper, as this is typically observed in semiconducting
materials[17,22] and one would expect to observe a more diffu-
sion-limited electron-transfer process in the case of pristine
metallic surfaces.[18,21] This effect is due to the presence of the
aforementioned CuO layer on the surface of copper that cre-
ates a metal–semiconductor junction. Therefore for copper, the
enhanced catalytic rate is due to the combination of LSPR and
formation of a metal–semiconductor junction where the latter
facilitates the separation of the photogenerated charge carriers
and provides more electrons for the reaction to occur at a faster
rate. Even though the observed response is a combination of
metal oxide/metal, when the reaction proceeds under the stim-
ulus of light, we observe a lower resistance to charge transfer
(decrease in the width of the semicircle). This implies that the
rate of electron transfer to [Fe(CN)6]3− and therefore the overall
reaction is significantly improved by photoirradiation. In con-
trast, for the silver system, we observe only a diffusion-limited
Table 1. Summary of the reaction rates observed for Cu@Cotton and Ag@Cotton.
Samples Reaction rate for
dark min–1
Reaction rate for
visible light min–1
Time taken for
dark min–1
Time taken for
visible light min–1
Cu Foil [12 mg] 0.01 0.09 110 45
Cu Foil [2 × 2 cm–359.2 mg] 0.12 0.32 23 8
Cu@Cotton 1.11 1.60 5 3
Ag Foil [12 mg] 0.01 0.03 500 390
Ag Foil [2 × 2 cm–430.3 mg] 0.09 0.14 50 35
Ag@Cotton 0.11 0.17 45 30

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electron transfer as evident from the absence of a semicircle
component. This implies that a semiconductor silver oxide
layer did not form in the case of silver, as was also evident from
Figures S2–S4 in the Supporting Information. This would be
expected, as silver is less prone to oxidation in comparison to
copper. However, as evident from the reduction in resistance
to charge transfer during photoexcitation of silver (Figure 4b
inset), light irradiation still leads to improvement in the rate of
electron transfer, which allows for improved catalytic rates upon
photoexcitation of Ag@Cotton fabric. For a true comparison
between Ag and Cu systems, we also intentionally fabricated
a Ag2O/Ag surface through forced surface oxidation of Ag and
probed the electron-transfer reaction (Figure S13, Supporting
Information). Although the Nyquist plot showed a small semi-
circle component, the reaction seemed to be still primarily gov-
erned by the diffusion of electrons. However, a clear decrease
in the resistance to charge transfer during visible light illumi-
nation could now also be observed in the case of the Ag2O/Ag
surface. In summary the lower activity for the silver system in
comparison to the copper system appears
to be predominantly due to the injection of
electrons into the silver (Figure 3) from the
thiosulphate ions under dark as well as illu-
minated conditions. These intricate details
from electrochemical investigations provide
convincing evidence that light irradiation of
copper metal (containing a thin oxide layer)
has a larger influence on the electron-transfer
ability of the catalyst over silver due to the
ease through which an oxide–metal junction
can be formed in the case of copper.
3. Conclusion
A facile strategy to create robust visible
light active metal catalysts on cotton fabrics
through the use of electroless deposition is
reported. The high porosity and hierarchical
ordering on the micrometer and nanometer
scale of cotton fabrics allowed access to a
large number of catalytically active metal
sites, which in combination with the metal
LSPR effect enhanced the catalytic rates.
Although Cu@Cotton showed superior cata-
lytic activity, Ag@Cotton fabrics showed
more robustness wherein the catalytic effi-
ciency was retained for at least 15 consecu-
tive catalytic cycles. This study provides
new mechanistic evidence on the electron-
transfer processes occurring during catalysis
under the influence of light. This allows us
to understand how the LSPR effect typically
shown by metal nanoparticles influences
electron-transfer processes. Finally, the pro-
posed facile strategy to directly fabricate
robust metal nanostructures on cotton fab-
rics can be widely used to create functional
textiles for industrial applications with an
ability to scale-up production. Therefore, this study is expected
to fuel future research to create metal-based catalyst surfaces
that expose catalytically active sites for their applicability in het-
erogeneous catalysis.
4. Experimental Section
FabricationofCu@CottonandAg@Cotton:ThefabricationofCu@Cotton
and Ag@Cotton was performed by the following process (Scheme 1):
An electroless metal deposition approach was employed for the
decoration of nanostructured metal (Ag and Cu) on individual fibers of
thread interwoven into a 3D cotton fabric purchased from local vendor.
The process started with sensitizing each fabric (2 cm × 2 cm) with
0.3 × 10−3 M SnCl2 aqueous solution for 30 min. Following a quick wash
with deionized water, the fabric was further immersed into 3 × 10−3 M
aqueous Pd(NO3)2 for 10 min. This formed an initial seed layer of Pd
nanoparticles that acted as nuclei for metal plating. Since Ag and Cu
deposition rates were different, to ensure that same amount of Ag and
Cu metal was deposited on fabrics, the metal deposition parameters
were optimized after the Pd sensitization step by performing Ag and Cu
a b
c d
100 500 900 1300
-0.8
-0.6
-0.4
-0.2
0.0
0.2
Potential/Vvs.Ag/AgCl
Time /s
100 500 900 1300
-0.8
-0.6
-0.4
-0.2
0.0
0.2
Time /s
100 500 900 1300
-0.8
-0.6
-0.4
-0.2
0.0
0.2
Time /s
100 500 900 1300
-0.8
-0.6
-0.4
-0.2
0.0
0.2
Time /s
Figure 3. OCP versus time recorded in a 30 mL solution containing 1 × 10−3
M [Fe(CN)6]3−
into
which S2O3
2−
was added after 200 s, as indicated by an arrow (black curves) and reaction
containing only S2O3
2−
as control (red curves) for a) copper in dark; b) copper in visible light;
c) silver in dark, and d) silver in visible light. (Control data has been translated horizontally to
coincide with the injection point of the catalytic run.)

FULLPAPER
plating at different temperatures (28, 45, 55, 65, 75 °C) and time points
(15, 30, 45, 60, 90, 120 min), followed by quantification of metal content
using atomic absorption spectroscopy (AAS). For Ag deposition, the
cotton fabric with Pd nuclei exposed at 28 °C to a silver plating solution
containing equimolar (1 M) quantities of diaminesilver(I) complex
([Ag(NH3)2]+
) and glucose solution (reducing agent) for 15 min were
used as the final material. For Cu deposition, the cotton fabric with
Pd nuclei exposed for 60 min at 55 °C to a copper plating solution
containing 0.3 M sodium potassium tartrate, 1 M NaOH, 0.1 M copper(II)
sulphate, and 1 M formaldehyde (reducing agent) were used as the final
material.
Characterization: The samples for SEM were prepared by immobilizing
the metal-coated cotton fabric sample on an aluminum stub. SEM
images were obtained using FEI Quanta SEM instrument operated at
an accelerating voltage of 30 kV. EDX analysis was carried out on the FEI
Quanta SEM fitted with an Oxford X-Max 20 Silicon Drift Detector. High-
resolution SEM images (Figure 1 a3 and b3 and insets therein) were
acquired using FEI Verios XHR-SEM instrument at the landing voltage
of 2 kV in conjunction with a monochromator to improve the surface
sensitivity of the images. X-ray diffraction measurements were carried
out on a Bruker D8 Advance XRD instrument operated at a voltage of
40 kV and a current of 40 mA with Cu Kα radiation. X-ray photoelectron
spectroscopy (XPS) measurements were carried out using Thermo
K-Alpha XPS instrument (Al Kα radiation, photon energy of 1486.6 eV).
The general scan and scans in the regions of C 1s, Cu 2p, Ag 3d,
and Pd 3d core levels binding energies were recorded at pass energy
of 20 eV. The core level spectra were fitted with a Shirley background
and chemically distinct species were resolved using a nonlinear least
squares fitting procedure. The core level BE were charge corrected with
adventitious carbon binding energy of 285 eV.
Heterogeneous Catalysis Reaction: The catalytic reactions were
carried out by performing the experiments under dark and visible
light illumination [Source: ThorLabs, warm white LED; power output
0.5 W, 10 cm working distance] conditions on a well-known model of
ferricyanide reduction (0.1 M thiosulphate and 1 × 10−3
M potassium
ferricyanide) in 30 mL reaction volumes at (28 ± 2) °C under stirring
conditions using 2 cm × 2 cm metal-loaded fabric as the catalyst. The
stirring rate was maintained at 1200 rpm using a magnetic stirrer.
The conversion of ferri- to ferro-cyanide was recorded as a function of
time using UV–vis spectroscopy (Cary 50 Bio spectrophotometer). The
catalyst reusability studies were performed by removing the catalyst
from the reaction vessel after completion of the reaction, followed by
washing the fabric three times with deionized water,
before being used for the subsequent cycle. Control
experiments were also carried out using the same
conditions without the presence of the catalyst, in
the presence of pristine cotton fabric, copper, and
silver foil of 12 mg weight, which is same as the
loading of these metals on the fabric as well as
2 × 2 cm2
Cu and Ag foil, which is same as the size
dimension of the metal fabric.
Electrochemical Measurements: The copper and
silver foils were first immersed in dilute HNO3
(10% v/v) for 5 min to remove any surface oxide
impurities and washed thoroughly with acetone and
methanol followed by drying in a stream of nitrogen
gas. Electrochemical measurements were recorded
using a CH Instruments electrochemical analyzer
at (28 ± 2) °C under dark and visible light. A three
electrode setup was used wherein the working
electrode consisted of the sample of interest (Ag
or Cu foil), the reference electrode was Ag/AgCl
(aqueous 3 M KCl) and a platinum wire was used as
the counter electrode. OCP versus time experiments
were carried out using 1 × 10−3
M [Fe(CN)6]3−
that
was initially present in the electrochemical cell and
stirred for a period of 200 s while the OCP versus
time data was recorded to establish a steady OCP
value at the surface. At this time, the required volume of S2O3
2−
was
injected into the cell to give a final concentration of 0.1 M and the OCP
versus time profile was continuously monitored. EIS experiments were
performed under quiescent conditions at the formal redox potential of
ferricyanide/ferrocyanide (5 × 10−3
M; 0.1 M NaCl) at amplitude of 10 mV
over a frequency range of 0.01–105
Hz.
Supporting Information
Supporting Information is available from the Wiley Online Library or
from the author.
Acknowledgements
S.R.A. and M.M. contributed equally to this work. V.B. thanks the
Australian Research Council for a Future Fellowship (FT140101285) and
research funding though ARC Linkage (LP100200859) grant scheme. V.B.
also acknowledges the generous support of the Ian Potter Foundation for
establishing an Ian Potter NanoBioSensing Facility at RMIT University.
R.R. acknowledges RMIT University for a Vice Chancellor’s Research
Fellowship. The authors acknowledge the support from the RMIT
Microscopy and Microanalysis Facility (RMMF) for technical assistance
and providing access to characterization facilities.
Received: October 12, 2015
Revised: December 3, 2015
Published online:
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