Content uploaded by Depanjan Sarkar
Author content
All content in this area was uploaded by Depanjan Sarkar on Aug 28, 2018
Content may be subject to copyright.
www.advmatinterfaces.de
COMMUNICATION
1800667 (1 of 7) © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Patterned Nanobrush Nature Mimics with Unprecedented
Water-Harvesting Efficiency
Depanjan Sarkar, Anindita Mahapatra, Anirban Som, Ramesh Kumar, Ankit Nagar,
Avijit Baidya, and Thalappil Pradeep*
DOI: 10.1002/admi.201800667
This is due to the fact that at any given
moment, the earth’s atmosphere contains
an astounding 37.5 million billion gallons
of water as vapor,[2] and an efficient device
to capture a fraction of this water vapor, in
a cost-effective way would help solve the
water crisis.
Over the period of human existence, it
has become apparent that biomimicking
is the most efficient way to tackle such
problems. When we look into nature,
there are organisms, which in the course
of evolution have acquired physical traits
that enabled them to capture atmos-
pheric water, even in the most arid cor-
ners of our planet. One such example
is the Stenocara beetle of Namib Desert
which capture water on its hardened fore-
wings.[3] Electron microscopic images of
these have revealed unique array of hydro-
philic regions distributed on a superhydro-
phobic background,[4] creating a surface
energy gradient, which facilitates efficient condensation and
transportation of atmospheric water. Another such example is
spider silk, which shows unique periodic spindle-knot struc-
ture when wetted and efficiently collects water from atmos-
phere through the combination of surface energy gradient and
Laplace pressure difference. Other inspirations from nature
are some cactaceae species which live in arid environments
and are extremely drought-tolerant.[5] These species are shown
to have structures with spines and trichomes which enable
them to condense humidity efficiently from the atmosphere.
Grasslands are also examples of natural atmospheric water har-
vesters. Hence, micro/nanostructuring of the water-collecting
surface plays a critical role in determining the efficiency of
water capture. With the advancement of nanotechnology, sig-
nificant efforts have been directed toward fabricating surfaces
with similar morphological features and chemical patterning to
enable efficient water capture.[6,7] However, these natural and
nature-mimicked surfaces collect atmospheric water in the
form of dew/fog and require the temperature to drop below the
dew point to cause condensation. For building a practical and
round-the-clock operating atmospheric water generator, it is
important to cool the condensing surfaces and the surrounding
air efficiently, with minimum energy input. Heat transfer effi-
ciency of the condensing surface material is as important as
the water transfer efficiency for creating a viable radiative con-
denser. Although many biomimetic, patterned surfaces have
been made for fog collection, inspired by active condensing
Water scarcity is one of the most alarming problems of the planet. An
ambient ion based method is developed to make hydrophilic-hydrophobic
patterned silver nanowires (NWs) as humidity harvesters of unprecedented
efficiency. Such water harvesters are developed by two-step surface
modification of the as-synthesized NWs (known from a report earlier) using
electrospray. These patterned NWs of ≈20 µm length and ≈200 nm width
grown over a relatively large area (2 × 2 cm2) exhibit atmospheric water
capture (AWC) efficiency of 56.6 L m−2 d−1, the highest reported so far.
The whole fabrication process of the surface is performed under ambient
conditions with a home-built nanoelectrospray ion source, without the help
of any sophisticated instrumentation. The synthesized material combines
and mimics two exciting examples of AWC in nature, which are cactae and
Namib Desert beetles, which utilize AWC for their living. It is believed that
the combination of the special features of the above two natural species helps
to achieve the highest water capture efficiency reported till date. A working
prototype using this surface for AWC is also fabricated.
Dr. D. Sarkar, A. Mahapatra, Dr. A. Som, R. Kumar, A. Nagar, A. Baidya,
Prof. T. Pradeep
DST Unit of Nanoscience (DST UNS) and Thematic Unit of Excellence
(TUE)
Department of Chemistry
Indian Institute of Technology Madras
Chennai 60036, India
E-mail: pradeep@iitm.ac.in
The ORCID identification number(s) for the author(s) of this article
can be found under https://doi.org/10.1002/admi.201800667.
Water Harvesting
Availability of clean fresh water is one of the measures of devel-
opment of a society. However, water resources have become
severely depleted or highly polluted due to the demands of
rapid economic growth as well as poor management in most
parts of the planet. This has resulted in water scarcity to be one
of the gravest social risks of the modern world while it was con-
sidered to be an environmental risk a few years ago.[1] Around
1.2 billion people, or almost one-fifth of the world’s popula-
tion already live in areas with water shortage, and another
500 million more people are being pushed to this situation. By the
year 2025, 1.8 billion people will be living in regions with sheer
water paucity, and two-thirds of the world’s population could
be living in water-stressed circumstances. Atmospheric water
capture is being considered as a possible solution for providing
clean water to people living in those areas, for sometime now.
Adv. Mater. Interfaces 2018, 1800667
www.advancedsciencenews.com
© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
1800667 (2 of 7)
www.advmatinterfaces.de
surfaces found in nature,[7,8] most of these make use of poly-
mers or polymer-hybrids, which might not be best suited for
radiative condensers due to their poor heat-transfer efficiencies.
Metallic nanostructures are of great interest in recent research
due to their excellent electrical and thermal conductivity.[9–11]
The enhanced electric field around these structures makes
them potential substrates for surface-enhanced Raman spec-
troscopy (SERS)[10,12] enabling sensing of various biological
and nonbiological compounds present in water.[13] Apart from
these, metallic nanostructures exhibit interesting mechanical
properties,[14] while maintaining high degree of porosity,[15]
ordered arrays,[16] and many more. Even though such nanostruc-
tures have potential applications in different areas, it has been
difficult to synthesize them over large areas for commercial
applications. Several methods have been developed to create pat-
terned nanostructures which include chemical[17] and physical[18]
vapor deposition, plasma chemical method,[19] spray pyrolysis,[20]
etc. They can also be synthesized using photolithography[21] or
electron beam lithography[9,22] as top-down approaches. Template
mediation[23] and self-assembly are also used for making desired
nanostructures. However, all these methods need special condi-
tions like vacuum, high temperature, templates, etc. Ambient,
solution state techniques to create well-defined metallic nano-
structures over large areas are still limited. In an earlier report
from our group, long (80 µm) nanowire (NW) arrays were made
through electrospray ionization-induced creation and deposition
of Ag nanoparticles (NPs), under ambient conditions.[24] These
wires could be grown over several cm2 areas to make a metallic
grassland like morphology. In this report, we have shown
growth of these structures over 4 cm2 area; however, they can
also be grown over several tens of cm2 area using a program-
mable moving stage.
Here, we report the creation of a hydrophilic-hydrophobic
patterned humidity-collecting surface as an efficient radiative
atmospheric water capture device, by chemical modification of
the metallic grasslands through electrospray deposition (ESD).
While the use of NW arrays maximize the available surface
area for water condensation, chemical modification of the NW
surface helps with the quick transfer of the condensed water
and regeneration of active sites for further condensation to
happen. The surface modification strategy also improved the
mechanical strength and stability of the NWs in water. In the
design of the surface, we have successfully fabricated surfaces
which mimic the hairy structures of cactae which in turn
have hydrophilic-hydrophobic patterns resembling the wings
of Stenocara beetles along with superior heat transfer capa-
bilities of metallic nanostructures. A combination of all these
effects led to high water capture efficiency (56.6 L d−1 m−2) at a
prototype-scale. Although we have used Ag NWs reported pre-
viously[24] as the initial building block of our patterned NWs,
the present work focuses on a method of creating hydrophilic-
hydrophobic patterned NWs using two simple steps, which
mimic the above mentioned examples from nature and com-
bine their special features to achieve highest water capture effi-
ciency reported till date.
Hydrophilic-hydrophobic patterned Ag NWs were fabricated
using ESD at room temperature in air. A schematic representa-
tion of the ESD process along with the dimensional descriptions
is shown in Figure S1 (Supporting Information). As the growth
of unpatterned NWs was described previously,[24] we present
only the essential aspects here. A detailed description of the
synthesis and characterization (electron microscopy, elemental
analysis) of the Ag NWs on an empty transmission electron
microscopy (TEM) grid, which form the core of the patterned
NWs, is given in the Supporting Information (Figures S2–S8,
Supporting Information). For all our AWC experiments, we
have selected stainless steel (SS) wire mesh as the substrate to
create a cost-effective substrate for the application. Figure S9a,b
(Supporting Information) shows scanning electron microscopy
(SEM) images of the Ag NWs grown on an empty TEM grid
and SS wire mesh, respectively, proving identical morphology
of the NWs on both the surfaces. Hence, for all our water cap-
ture experiments, we used the hydrophilic-hydrophobic pat-
terned Ag NWs grown on SS wire meshes (50 µm). Use of a
larger mesh size would reduce the active area for water conden-
sation because of the reduction of number of wires (on which
the Ag NWs are grown) in a specified area. On the other hand,
use of a lower mesh size would increase the number of wires
(on which the Ag NWs are grown) but it would also reduce
the active surface area by affecting the size of the Ag NWs.
The Ag NWs grown on a reduced mesh size SS wire mesh were
smaller in size because of the coulombic repulsion between the
growing NWs. We have also compared the growth of these NWs
on top of meshes of different shapes.
Figure 1a shows a SEM image of the as-synthesized Ag NWs
on a SS wire mesh using ESD. It shows an arrangement of
1D NWs, which upon extension will resemble a grassland-like
structure. This can be created over a larger area of the order of
Adv. Mater. Interfaces 2018, 1800667
Figure 1. Electron microscopic characterization of the hydrophilic-hydrophobic patterned Ag NWs. a) SEM image of the as-synthesized Ag NWs on
a 50 µm SS wire mesh, b) SEM image of similar NWs after fluorothiol coating. Difference in contrast is due to the organic content. c) TEM image of
the FT-coated Ag NWs, showing the intact morphology of the material, EDS spectrum (inset) showing presence of F, S, and Ag. Cu is due to the grid.
www.advancedsciencenews.com
© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
1800667 (3 of 7)
www.advmatinterfaces.de
4 cm2. Figure S10 (Supporting Information) shows a large-area
SEM image (300 µm2) of the Ag NWs on a TEM grid. These
metallic NWs were the core of the patterned NWs with specific
hydrophilic regions on a hydrophobic background. Fabrication
of the patterned NWs was designed by successive ESD pro-
cesses, as explained below.
At first, as-synthesized Ag NWs were subjected to
an electrospray coating of a fluorothiol (FT), namely,
3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluoro-1-de-
canethiol. A solution in dichloromethane (DCM) and acetoni-
trile (AcN) mixture was used for ESD of FT. This made the Ag
NWs superhydrophobic in nature by the formation of a chem-
ical bond between Ag and the thiol group, of the FT. Metal–
sulfur bond is strong and is the basis of one class of self-assem-
bled monolayers.[25] Figure 1b shows a SEM image of FT-coated
Ag NWs. The change in contrast (with the image in Figure 1a) is
due to the coating of a nonconducting layer of FT on the metal.
To prove the superhydrophobic nature of the surface, the con-
tact angle of a water droplet on it was measured. Surface energy
of the FT-coated surface was so low that a water droplet did not
stand static on the surface. Figure S11 (Supporting Informa-
tion) shows images of a water droplet rolling on the FT-coated
Ag NWs. No pinning of the droplet was observed, proving the
superhydrophobicity of the surface. Figure S12a–c (Supporting
Information) shows optical images of a water droplet bouncing
off from the FT-coated Ag brush substrate while another water
droplet is stranded on the bare stainless steel wire mesh. This
proves that the FT coating on the Ag brushes made them supe-
rhydrophobic in nature. Figure S12d (Supporting Information)
shows contact angle measurement of a water droplet on stain-
less steel wire mesh before (normal wire mesh) and after modi-
fication (FT-coated Ag NWs). Contact angle of the water droplet
was measured to be ≥125° in the case of normal mesh indi-
cating that the normal stainless steel surface is hydrophobic
(90° <
θ
c < 150°). Measurement of resting contact angle was not
possible for the superhydrophobic surface as it was too slippery
for the droplet to sit on it. Hence, the contact angle was meas-
ured when the water droplet was touching the surface. A meas-
urement of advancing and receding contact angles (173° and
166°, respectively) was also performed (Figure S13, Supporting
Information). The contact angle hysteresis (173°–166° = 7°),
is within the desired 10° for good superhydrophobicity. These
measurements prove the superhydrophobic nature of the Ag
NWs after FT coating. Roughness due to the presence of NWs
also plays a significant role in acquiring superhydrophobicity.
Control experiments were performed with normal stainless
steel wire mesh and using the same sprayed with FT. It was
seen that water droplets did not bounce off from the normal
stainless steel mesh but wetted it instead, shown in Figure S14a
(Supporting Information), clearly indicating that it was not
superhydrophobic. Then FT was sprayed on the stainless steel
mesh and the same experiment was repeated, images of which
are shown in Figure S14b (Supporting Information). Here also
the droplets did not bounce off and got stuck to the surface.
However, when sprayed over by FT, the stainless steel mesh
surface becomes hydrophobic to some extent. Hence, the pres-
ence of Ag NWs, providing surface roughness in nm scale, was
essential to make it superhydrophobic. ESD is a gentle process;
hence, it does not harm the morphology of the as-synthesized
nanobrushes. This was the prime reason for us to choose ESD
of FT over Ag NWs. Other procedures of FT coating, such
as spray coating with a mechanical sprayer were not useful.
Although the spray-coated surface became superhydrophobic, it
destroyed the morphology of the NWs (Figure S15, Supporting
Information). To optimize the ESD time for FT coating, a time-
dependent ESD experiment was performed (spray time of 2, 4,
6, 8, and 10 min) on five different spots containing identical
Ag NWs. It was observed that each spot became superhydro-
phobic proving that ESD of FT for 2 min was enough to make
the surface superhydrophobic. However, these FT-coated NWs
lost their morphology when subjected to water wash. In view of
that we have enhanced the ESD time of FT to 20 min at a rate
of 20 nA deposition current. In this case, the FT-coated NWs
retained their morphology after water wash. This indicates
that ESD of FT also has a role in imparting stability to the Ag
nanobrushes by AgS bond formation (there is another aspect
how ESD of FT provides stability to the Ag NWs which will be
discussed at the end of this paragraph). Hence, for all other
experiments, the above mentioned time and rate of ESD was
taken as optimum. Figure 1c shows a TEM image of the FT-
coated Ag NWs. Inset in Figure 1c shows an energy-dispersive
spectrum (EDS) taken from these NWs showing the presence
of all the expected elements (Ag, S, and F).
From our data we know that our Ag NWs are made by an
organization of NPs. During the ESD of FT on Ag NWs, the
NPs constituting the NWs coalesce with each other, making
a solid metallic core inside. Figure S16 (Supporting Informa-
tion) shows the TEM images of the Ag NWs before and after FT
coating. From these images, we can easily compare and come to
a conclusion that the NPs in the FT-coated Ag NWs are fused,
providing a solid core on which the superhydrophobic coating
of FT is formed. This solid metallic core gives strength to the
NWs, making them more resistant toward mechanical strain.
In the second step, we have performed ESD of AgOAc
(aqueous solution, 10 × 10−3 m) over the superhydrophobic
NWs to create Ag NP decorated NWs. These bare Ag NPs act as
hydrophilic protrusions on the superhydrophobic NWs. In the
following paragraph, we describe the structure of our material
using electron microscopic images. The contact angle of a water
droplet was measured after creating the hydrophilic zones.
Figure S17 (Supporting Information) shows that the contact
angle of a water droplet was 152°. Reduction of the contact
angle, with respect to the superhydrophobic NWs, proves the
presence of hydrophilic protrusions.
In Figure 2, we represent our material and compare it with
the examples available in nature. Figure 2a shows a cartoon of
a cactus with water droplets on the trichomes. Figure 2b shows
a schematic of the cactus showing that its sharp spines and tri-
chomes are responsible for water capture. Figure 2c shows a
TEM image of our material which resembles the hairy structure
of a cactus although the scales shown are different. Figure 2d
shows a cartoon of a Stenocara beetle and the hydrophobic-
hydrophilic patterning of the wings (Figure 2e). Figures 2f,g
show a schematic of the synthesized hydrophilic-hydrophobic
patterned Ag NW and a TEM image of the same with three
distinct regions: (i) the Ag-core, (ii) hydrophobic coating on the
Ag-core, and (iii) tiny hydrophilic regions (Ag NPs, see below
for its synthesis) on the hydrophobic background. Ag core gives
Adv. Mater. Interfaces 2018, 1800667
www.advancedsciencenews.com
© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
1800667 (4 of 7)
www.advmatinterfaces.de
the strength to the brushes, while the FT coating creates the
hydrophobic background. Subsequent ESD of Ag on this FT-
coated surface resulted in Ag NPs decoration all over the NWs.
These Ag NPs, embedded in the FT layer, act as hydrophilic
zones, known to be responsible for the condensation of atmos-
pheric water. A schematic illustration of atmospheric water cap-
ture by these hydrophilic-hydrophobic patterned NWs is shown
in Figure 2f.
A 2 cm × 2 cm SS wire mesh covered by these patterned
NWs was created and used for water capture experiments
described in the following sections. Evaluation of humidity
condensation was performed using this surface mounted on
a Peltier cooler, which was then videographed (Video S1, Sup-
porting Information) using a microscope. Two experiments,
one control (with normal stainless steel mesh) and another
with the prepared surface, were performed to test the effi-
ciency of the nanostructured material for atmospheric water
capture. In both the experiments, the surface being examined
was carefully mounted on a Peltier cooler, using silver paste as
glue, so that it remained in adequate contact with the cooling
stage. The entire arrangement was placed atop the viewing
stage of an inverted fluorescence microscope (Leica), in a con-
trolled room with 40% relative humidity and 28 °C tempera-
ture (the dew point at this condition ≈13 °C). An arrangement
was made for illumination of the surface being examined, for
the purpose of microscopy. Time-lapse optical microscopy of
the stainless steel mesh as well as the prepared surface upon
exposure to cool humid air was performed to monitor droplet
nucleation and condensation. The temperature of the surface
under examination was maintained at 12 °C, measured with a
thermocouple. Figure S18a,b (Supporting Information) shows
the optical images of a normal stainless steel wire mesh
after 60 and 120 s of collection, respectively. Condensation
of water droplets was seen on the wire mesh. Figure S18c,d
(Supporting Information) shows the optical images of con-
densation of water on the stainless steel wire mesh containing
superhydrophobic Ag NWs with hydrophilic protrusions. It is
seen that the amount of water captured in this case is much
larger in comparison to a normal wire mesh. In a time span of
2 min, a volume of 2.6 × 10−6 L water was captured (approxi-
mately calculated from the number of droplets considering
them to be spheres, ≈1.3 × 10−8 L of water was captured over
the normal SS wire mesh) on the brushes, even though the
humidity was less and no water vapor was forcefully passed
over the surface during the experiment. The video clearly
shows nucleation of tiny water droplets on the patterned
NWs followed by fusion of them to bigger droplets. Once the
droplet is larger in size, it rolls off the surface because of its
superhydrophobic nature.
Transport of the condensed water is a crucial criterion of any
atmospheric water capture material. Hence, we calculated the
water collection rate of the surface on a 2 × 2 cm2 area con-
sidering all the parameters like, condensation rate, transport of
the collected water, etc. Figure 3a shows an optical photograph
of the total setup where the hydrophilic-hydrophobic patterned
NWs containing SS wire mesh was firmly mounted (the black
Adv. Mater. Interfaces 2018, 1800667
Figure 2. Graphical demonstration of the natural species with atmospheric water-harvesting capabilities, illustration of their special properties and
comparison with our material. a) Graphical representation of a cactus, b) illustration of hairy structure of cactus, c) TEM image of a single Ag
NW showing similar hairy structures resembling the cactus, d) graphical representation of a Stenocara beetle collecting water from atmosphere,
e) schematic representation of hydrophobic-hydrophilic patterning of their wings, f) illustration of our superhydrophobic-hydrophilic patterned Ag NW
showing a solid Ag core, a superhydrophobic coating on the core, and hydrophilic regions (Ag NPs) on the superhydrophobic background, and g) TEM
image of a single Ag NW showing all three regions.
www.advancedsciencenews.com
© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
1800667 (5 of 7)
www.advmatinterfaces.de
square surface) on a Peltier cooler, using a carbon tape. Carbon
tape was used in this case, instead of silver paste, for better
transport of the collected water. Inset of Figure 3a shows a
photograph of the surface. A 12 V DC fan was used for cooling
the hot side of the Peltier cooler. Temperature of the surface
was measured and kept constant (7.5 °C) during the experi-
ment. The above experiment was performed inside an air-
conditioned room where the relative humidity was 48% and the
ambient temperature was 26 °C. There was no forced airflow.
Figure 3b shows the formation of water droplets on the hydro-
philic-hydrophobic patterned nanobrushes, just after switching
on the Peltier cooler. Figure 3c shows an optical microscopic
image of the surface at 100× magnification, clearly showing the
accumulated droplets on it. In the above experiment, 3.75 mL
of water was collected in 13 h. If we convert the water collection
to L d m−2 area, it comes to 7.9 L. Figure 3d shows an optical
photograph of the collected water in a 2 mL vial. Control experi-
ments were performed to compare the water capture efficiency
of the hydrophilic-hydrophobic patterned NWs with as-synthe-
sized Ag NWs and hydrophilic Ag NWs. Although the parent
surfaces without chemical functionalization were unstable
during water capture experiments, we made the structures
stable by exposing them to 4-mercaptobenzoic acid. In addi-
tion to enhanced stability during water capture, this function-
alization made the surface hydrophilic. Such surfaces showed a
water capture efficiency of 4.3 L d−1 under the same conditions
as before.
For the next set of experiments, we designed a prototype
to evaluate the water capture efficiency of the surface in pres-
ence of air flow. Figure 4a shows a schematic of the prototype.
In these experiments, a 12V DC (air flow speed of 2.55 m s−1
volume 103–105 cfm) fan was used to blow atmospheric air
toward the cold hydrophilic-hydrophobic patterned surface.
Two sets of experiments were performed with this proto-
type: (i) inside an air-conditioned room (at lower humidity)
(Figure 4b shows an optical photograph of the setup), and
(ii) outside the lab, under ambient conditions (Figure 4c shows
a photograph). Conditions and data collected from these experi-
ments are described here. In the first set of experiments, sur-
face temperature and average relative humidity were 8 °C
and 58%, respectively. The water collection efficiency was
26.8 L d−1 m−2. In the second set of experiments, the temper-
ature of the surface was kept the same and average relative
humidity was ≈87%. In this case, the water collection efficiency
was 56.5 L d−1 m−2. This is the highest water collection reported
till date by any surface. The high efficiency of water collection
can be attributed to the combination of cactus effect as well as
hydrophilic-hydrophobic patterning. Water droplets start nucle-
ating on the hydrophilic regions and as they grow larger in size,
they start to roll off from the surface, generating fresh surface
for collection.
For long-term use of the substrate, stability of the brushes
is an important aspect. Reusability and the morphology of
the surface were checked after the water capture experiment.
Figures S19a,b (Supporting Information) show SEM images
of the hydrophilic-hydrophobic patterned Ag nanobrushes
after five cycles of water capture. The images show that the
morphology of the brushes is almost intact after the experi-
ment. Figures S19c,d (Supporting Information), respectively,
show contact angle measurements of a water droplet on the
substrate before and after the water capture experiment. The
contact angle was found to be the same in both the cases,
proving that the nature of the surface is the same after dew
collection.
An ambient solution-state method of creating hydrophilic-
hydrophobic patterned 1D Ag NWs, using electrospray deposi-
tion in three simple steps, is presented. The whole synthesis
including the Ag NWs (the core of the patterned NWs) was per-
formed at room temperature without the help of any sophisti-
cated instrumentation. This method of synthesis enabled us to
create a material that could mimic two efficient natural atmos-
pheric water harvesters. Combination of hydrophilic patterns
on a superhydrophobic background along with hairy struc-
tures of the Ag NWs led to highest water capture efficiency,
reported till date. We also built a prototype and tested its water
capture efficiency under various conditions. At ≈87% relative
humidity, our material showed a water capture efficiency of
56.5 L d−1 m−2.
Experimental Section
For all experiments, nanospray emitters were made using a micropipette
puller (P-97) purchased from Sutter Instrument, USA. To confirm the
Adv. Mater. Interfaces 2018, 1800667
Figure 3. Optical and microscopic photographs of the condensed water
droplets on a 2 × 2 cm2 area. a) Optical photograph of the water collection
setup. Inset shows a photograph of the hydrophilic-hydrophobic patterned
surface over a 2 × 2 cm2 area. Each ESD results in a 5 mm dia dark
colored disk indicating the growth of NWs. This process was repeated
multiple times to cover the 2 × 2 cm2 area. b) Zoomed optical photograph
of the surface after switching on the Peltier cooler showing condensed
water droplets on it and dripping of water at the bottom of the surface.
c) Optical photograph (at a 100× magnification) of the Ag NWs with
condensed water droplets. d) Optical photograph of the collected water
in a 2 mL vial.
www.advancedsciencenews.com
© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
1800667 (6 of 7)
www.advmatinterfaces.de
presence of solvated Ag+ ions, mass spectra were collected using an
ion trap LTQ XL (Thermo Scientific, San Jose, CA) mass spectrometer.
Indium tin oxide-coated glass slides (Toshniwal brothers (SR) Pvt. Ltd.,
India) was the usual deposition substrate. Locally available stainless
steel wire mesh was used as a surface to grow the Ag NWs. All TEM
measurements were performed using a JEOL 3010 (JEOL Japan)
transmission electron microscope. Copper TEM grids were purchased
from SPI Supplies. A FEI Quanta 100 instrument with tungsten filament
source was used for SEM imaging. EDS analyses were performed with
an attachment on the SEM instrument. Contact angle and contact angle
hysteresis (CAH) of water droplet on the different coated substrates were
measured using a Holmarc contact angle meter. Optical photographs of
water droplets condensed over the hydrophilic-hydrophobic patterned Ag
NWs and normal SS mesh was performed using a 100× objective fitted
to a Leica DFC365 FX microscope. Optical photographs of the surface,
prototype, and water droplets bouncing off the surface were captured
using a Nikon D5100 camera using an 18–55 mm lens. Videos were also
captured using the same camera.
Supporting Information
Supporting Information is available from the Wiley Online Library or
from the author.
Acknowledgements
T.P. acknowledges financial support from the Department of Science
and Technology, Government of India for his research program on
nanomaterials. D.S. thanks the University Grants Commission for a
research fellowship. A.S. thanks Council of Scientific and Industrial
Research for a research fellowship.
Conflict of Interest
The authors declare no conflict of interest.
Keywords
nature mimics, prototype, superhydrophobic-hydrophilic patterned
NWs, water harvesting
Received: May 2, 2018
Revised: June 17, 2018
Published online:
[1] Global Risks Report by World Economic Forum, 2017.
[2] https://whyfiles.org/2010/how-much-water-is-in-the-atmosphere/
index.html (accessed: 2010).
[3] a) A. R. Parker, C. R. Lawrence, Nature 2001, 414, 33; b) S. M. Kang,
I. You, W. K. Cho, H. K. Shon, T. G. Lee, I. S. Choi, J. M. Karp, H. Lee,
Angew. Chem., Int. Ed. 2010, 49, 9401; c) X. Zeng, L. Qian, X. Yuan,
C. Zhou, Z. Li, J. Cheng, S. Xu, S. Wang, P. Pi, X. Wen, ACS Nano
2017, 11, 760; d) J. Hou, H. Zhang, Q. Yang, M. Li, Y. Song, L. Jiang,
Angew. Chem., Int. Ed. 2014, 53, 5791; e) B. White, A. Sarkar,
A.-M. Kietzig, Appl. Surf. Sci. 2013, 284, 826; f) S. G. Naidu, J. Insect
Physiol. 2001, 47, 1429.
Adv. Mater. Interfaces 2018, 1800667
Figure 4. Prototype of the atmospheric water capture experiment. a) Schematic and b,c) photographs of water capture experiments inside and outside
the laboratory. The photograph in (c) shows that the air inlet of the prototype is kept outside the laboratory window.
www.advancedsciencenews.com
© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
1800667 (7 of 7)
www.advmatinterfaces.de
Adv. Mater. Interfaces 2018, 1800667
[4] J. Hou, H. Zhang, Q. Yang, M. Li, Y. Song, L. Jiang, Angew. Chem.,
Int. Ed. Engl. 2014, 53, 5791.
[5] J. Ju, H. Bai, Y. Zheng, T. Zhao, R. Fang, L. Jiang, Nat. Commun.
2012, 3, 2253/1.
[6] a) H. Bai, L. Wang, J. Ju, R. Sun, Y. Zheng, L. Jiang, Adv. Mater.
2014, 26, 5025; b) G.-T. Kim, S.-J. Gim, S.-M. Cho, N. Koratkar,
I.-K. Oh, Adv. Mater. 2014, 26, 5166; c) M. Cao, J. Ju, K. Li, S. Dou,
K. Liu, L. Jiang, Adv. Funct. Mater. 2014, 24, 3235; d) H. Zhu,
Z. Guo, W. Liu, Chem. Commun. 2016, 52, 3863; e) K.-C. Park,
P. Kim, A. Grinthal, N. He, D. Fox, J. C. Weaver, J. Aizenberg,
Nature 2016, 531, 78; f) S. K. Nune, D. B. Lao, D. J. Heldebrant,
J. Liu, M. J. Olszta, R. K. Kukkadapu, L. M. Gordon, M. I. Nandasiri,
G. Whyatt, C. Clayton, D. W. Gotthold, M. H. Engelhard,
H. T. Schaef, Nat. Nanotechnol. 2016, 11, 791.
[7] S. C. Thickett, C. Neto, A. T. Harris, Adv. Mater. 2011, 23, 3718.
[8] D. T. Edmonds, F. Vollrath, Proc. R. Soc. London, Ser. B 1992, 248, 145.
[9] S. A. Maier, P. G. Kik, H. A. Atwater, S. Meltzer, E. Harel, B. E. Koel,
A. A. G. Requicha, Nat. Mater. 2003, 2, 229.
[10] M. Moskovits, J. Raman Spectrosc. 2005, 36, 485.
[11] H. Wang, D. W. Brandl, P. Nordlander, N. J. Halas, Acc. Chem. Res.
2007, 40, 53.
[12] a) K. A. Willets, R. P. Van Duyne, Annu. Rev. Phys. Chem. 2007, 58,
267; b) P. L. Stiles, J. A. Dieringer, N. C. Shah, R. P. Van Duyne,
Annu. Rev. Anal. Chem. 2008, 1, 601.
[13] a) L. Zhang, F. X. Gu, J. M. Chan, A. Z. Wang, R. S. Langer,
O. C. Farokhzad, Clin. Pharmacol. Ther. 2008, 83, 761; b) J. N. Anker,
W. P. Hall, O. Lyandres, N. C. Shah, J. Zhao, R. P. Van Duyne,
Nat. Mater. 2008, 7, 442; c) A. Kolmakov, M. Moskovits,
Annu. Rev. Mater. Res. 2004, 34, 151.
[14] a) Z. W. Pan, Z. R. Dai, Z. L. Wang, Science 2001, 291, 1947
b) Z. L. Wang, J. Song, Science 2006, 312, 242.
[15] a) K. Hristovski, P. Westerhoff, J. Crittenden, J. Hazard. Mater.
2008, 156, 604; b) Y. Han, X. Wu, Y. Ma, L. Gong, F. Qu, H. Fan,
CrystEngComm 2011, 13, 3506; c) X. Wang, W. Cai, Y. Lin, G. Wang,
C. Liang, J. Mater. Chem. 2010, 20, 8582.
[16] X. Wang, C. J. Summers, Z. L. Wang, Nano Lett. 2004, 4, 423.
[17] a) A. Y. Khodakov, W. Chu, P. Fongarland, Chem. Rev. 2007,
107, 1692; b) K. L. Choy, Prog. Mater. Sci. 2003, 48, 57; c) L. Hu,
D. S. Hecht, G. Gruener, Chem. Rev. 2010, 110, 5790; d) M. Kumar,
Y. Ando, J. Nanosci. Nanotechnol. 2010, 10, 3739.
[18] a) Y. C. Kong, D. P. Yu, B. Zhang, W. Fang, S. Q. Feng,
Appl. Phys. Lett. 2001, 78, 407; b) M. M. Hawkeye, M. J. Brett,
J. Vac. Sci. Technol., A 2007, 25, 1317; c) U. Helmersson,
M. Lattemann, J. Bohlmark, A. P. Ehiasarian, J. T. Gudmundsson,
Thin Solid Films 2006, 513, 1.
[19] R. P. Garrod, L. G. Harris, W. C. E. Schofield, J. McGettrick,
L. J. Ward, D. O. H. Teare, J. P. S. Badyal, Langmuir 2007, 23,
689.
[20] a) T. Xia, M. Kovochich, M. Liong, L. Madler, B. Gilbert,
H. Shi, J. I. Yeh, J. I. Zink, A. E. Nel, ACS Nano 2008, 2, 2121;
b) G. L. Messing, S. C. Zhang, G. V. Jayanthi, J. Am. Ceram. Soc.
1993, 76, 2707; c) S. A. Studenikin, N. Golego, M. Cocivera,
J. Appl. Phys. 1998, 84, 2287; d) I. Cesar, A. Kay, J. A. G. Martinez,
M. Graetzel, J. Am. Chem. Soc. 2006, 128, 4582.
[21] a) Y. Xia, G. M. Whitesides, Angew. Chem., Int. Ed. 1998, 37, 550;
b) Y. Xia, J. A. Rogers, K. E. Paul, G. M. Whitesides, Chem. Rev. 1999,
99, 1823; c) G. M. Whitesides, E. Ostuni, S. Takayama, X. Jiang,
D. E. Ingber, Annu. Rev. Biomed. Eng. 2001, 3, 335; d) E. W. H. Jager,
E. Smela, O. Inganas, Science 2000, 290, 1540.
[22] a) L. Jiao, L. Zhang, X. Wang, G. Diankov, H. Dai, Nature
2009, 458, 877; b) S. A. Maier, M. L. Brongersma, P. G. Kik,
S. Meltzer, A. A. G. Requicha, H. A. Atwater, Adv. Mater. 2001, 13,
1501.
[23] a) B. Freund, S. Suresh, Thin Film Materials Stress, Defect Formation
and Surface Evolution, Cambridge University Press, Cambridge
2003; b) S. I. Stupp, V. LeBonheur, K. Walker, L. S. Li, K. E. Huggins,
M. Keser, A. Amstutz, Science 1997, 276, 384; c) J. V. Barth,
G. Costantini, K. Kern, Nature 2005, 437, 671; d) Y. Zhang,
L. Zhang, C. Zhou, Acc. Chem. Res. 2013, 46, 2329; e) H.-W. Liang,
S. Liu, J.-Y. Gong, S.-B. Wang, L. Wang, S.-H. Yu, Adv. Mater. 2009,
21, 1850.
[24] D. Sarkar, M. K. Mahitha, A. Som, A. Li, M. Wleklinski, R. G. Cooks,
T. Pradeep, Adv. Mater. 2016, 28, 2223.
[25] C. Vericat, M. E. Vela, G. Corthey, E. Pensa, E. Cortes,
M. H. Fonticelli, F. Ibanez, G. E. Benitez, P. Carro, R. C. Salvarezza,
RSC Adv. 2014, 4, 27730.
