Porous Carbon Nanoparticle Networks with Tunable Absorbability
Wei Dai1, Seong Jin Kim1, 2, Won-Kyeong Seong1, Sang Hoon Kim1, Kwang-Ryeol Lee1,
Ho-Young Kim2, and Myoung-Woon Moon1,*
1
Institute for Multi-disciplinary Convergence of Matters, Korea Institute of Science and Technology,
Seoul 130-650, Republic of Korea
2
School of Mechanical and Aerospace Engineering, Seoul National University, Seoul 151-744,
Republic of Korea
* To whom correspondence should be addressed: [email protected]
Table of contents
1. Fig. S1: N2 BET analysis of the porous CNPs network
2. Fig. S2: Comparison of water CAs on flat carbon coating and porous CNPs networks
3. Fig. S3: Influence of fluorine incorporation on the CA of flat carbon coatings
4. Fig. S4: Wetting behavior of oil on porous carbon under water
5. Fig. S5: Separation of the stirred oil/water mixture using porous carbon
6. Videos S1-S4
References
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1. N2 BET analysis of the porous CNPs network
The typical adsorption isotherms for N2 on the porous carbon coatings prepared at 500 mTorr
are presented in Fig. S1 to characterize the porous structure of the carbon materials. Figure S1(a)
shows a type-IV nitrogen sorption isotherm with a small hysteresis loop of type H3, which
indicates the existence of different pore sizes ranging from micro- to macro-pores1, 2. There is a
rapid increase in the adsorption at a low pressure, corresponding to the presence of micropores.
The desorption hysteresis at a medium relative pressure is related to the presence of the developed
mesopores, and the nearly vertical tails at a relative pressure of approximately 1.0 indicate the
presence of macroporosity. Accordingly, the hierarchical porous structure of the as-deposited
porous carbon is composed of micropores, mesopores and macropores. The pore size distributions
of the porous carbon as calculated from the nitrogen desorption branches by a
Barrett–Joyner–Halenda analysis are presented in Fig. S2(b)1. This figure shows that the
as-deposited porous carbon network displays a typical hierarchical pore size distribution, with the
highest peak centered at 34 nm and several lower peaks centered at 15 nm and 5 nm. It is clear that
the majority of pores in the as-deposited porous carbon are mesopores.
Specific surface areas of the porous carbon and F-porous materials were measured using the BET
method according to the adsorption isotherms 1. It can be seen that the pure porous carbon (0/20)
has a specific surface area of 148 m2/g, while the F-porous carbon materials show relatively large
specific surface areas of about 200 m2/g. This indicates that the incorporation of CF4 increased the
porosity of the porous carbon.
2
Figure S1 | N2 BET analysis of the porous CNPs network. (a) Typical N2 adsorption isotherms on
porous carbon materials deposited at 500 mTorr and the corresponding pore size distribution (inset
graph). (b) Specific surface areas of the porous carbon materials deposited at various CF4/C2H2
ratios.
2. Comparison of water CAs on flat carbon coating and porous CNPs networks
Figure S2 | Contact angles (CAs) of DI water on the as-deposited carbon materials. (a) Flat
carbon coatings deposited at 100 mTorr. (b) Porous CNP networks deposited at 500 mTorr.
Figure S2 (a) and (b) present the CAs of DI water droplets placed on the flat carbon coatings
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deposited at a relatively low pressure of 100 mTorr and porous CNP network coatings deposited at a
relatively high pressure of 500 mTorr, respectively. The flat carbon coating shows water CAs of
approximately 60o, similar to the values typical of amorphous carbon (or diamond-like carbon)
coatings 3.
3. Influence of fluorine incorporation on the CA of flat and porous carbon coatings
Figure S3 | CAs on flat and porous carbon coatings. CAs of (a) DI water and (b) ethylene glycol
(E.G.) are shown as a function of the CF4/C2H2 ratio.
Figures S3 (a) and (b) show the CAs of water and E.G. as measured on flat carbon coatings
deposited at 100 mTorr and porous carbon coatings deposited at 500 mTorr at various CF4/C2H2
ratios. In this study, except for the deposition pressure, the other deposition parameters of the flat
carbon coatings are identical to those of the porous carbon nanoparticle (CNP) network coatings. It
can be seen that the water CA on both the flat carbon coatings and porous carbon coatings increased
monotonously as the ratio of CF4/C2H2 increased in the gas mixture. However, the CA values on the
surfaces of the porous carbon coatings are sharply higher than those on the surfaces of the flat
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carbon coatings. For E.G., which has a surface energy of 47.7 mJ/m2 at 20 ℃ (the surface energy of
DI water is 72.8 mJ/m2), the carbon coatings, both the flat and porous samples deposited at low
CF4/C2H2 ratios (i.e., 5/15 and 0/20) show complete oil-wetting behavior with a CA of
approximately 0o. However, when the CF4/C2H2 ratio exceeded 10/10, the CA of the flat carbon
surface increased monotonously to 82.5o while the CA of the porous case increased to 160o. It is
clear that the porous structure plays a significant role in the superhydrophobicity of water and E.G.
and that the incorporation of fluorine can dramatically improve the repellence. The combination of
the porous structure and fluorination allows the superhydrophobicity of F-porous carbon on both
water and E.G. However, for silicone oil, all of the samples, regardless of the CF4 fraction, showed
complete oil-wetting behavior due to its very low surface energy of 21.2 mJ/m2 at 20 ℃.
4. Wicking behavior of silicone oil on porous carbon under water
In order to verify the result in a water environment, we put the porous carbon film under the
water surface, as indicated in Fig. S4(a). Then, we placed a single silicone oil droplet on the film
under the water and took a video of the process of oil droplet absorption into the specimen using a
high-speed camera from a top view. For visualization, we dyed the oil droplet in blue. We noted
the oil bulk droplet placed on the surface wicking through the film, as indicated in the sequential
images in Figs. S4 (c-f). Moreover, when we measured the wicking length (L) from the bulk
droplet edge to the wicking front, we found that this length followed Washburn’s equation of
L~t1/2, as shown in Fig. S4(b), which is widely known to apply due to the wicking dynamics5.
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Figure S4 | Wicking behavior of oil on porous carbon under water: (a) Schematic of a silicone
oil drop approaching porous carbon coatings under water. (b) The wicking length (L) from the bulk
droplet edge to the wicking front as a function of the wicking time (t). (c~f) Time sequential images
of a silicone oil droplet placed on porous carbon coatings under water. The arrows facing each other
in (f) indicate the thickness of the wicking front. The scale bar is 2 mm.
5. Separation of stirred oil /water mixture using porous carbon
Figure S6 shows the separation of the oil/water mixture during stirring. We sought to determine
whether or not small oil droplets floating under water would easily be absorbed by porous carbon.
We created the stirred oil/water mixture by mixing silicone oil (dyed in blue) and water at a ratio
of 1/300 and then shaking it 100 times by hand. Then, a coupon-shaped porous carbon cake was
put into the stirred oil/water mixture reservoir. It was found that the color of the oil/water mixture
changed from blue to transparent, indicating that a significant amount of silicone oil was absorbed
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into the porous carbon specimen, as shown in the sequential images in Fig. S6.
Figure S5 | Photographic images showing the separation of the stirred oil/water mixture using
a cake-shaped sample with a porous carbon particle network. (a) An optical image of the stirred
oil/water mixture. (b) An image, taken after 1 sec later, showing that the porous carbon cake was
put into the stirred oil/water mixture. (c) The stirred oil/water mixture after selective absorption by
the porous carbon cake after 50 min.
6. Videos S1-S4
Video S1. A water droplet placed on F-porous CNP network coating/filter paper (the water was
dyed red). The sample showed perfect hydrophobicity, and the water droplet could not penetrate
into the surface of the F-porous CNP network coating.
Video S2. A silicone oil droplet placed on F-porous CNP network coating/filter paper (the silicone
oil was dyed light blue). The silicone oil was quickly absorbed by the porous F-CNP network.
Video S3. A droplet of water/silicone oil mixture placed on F-porous CNP network coating/filter
paper. The water and oil were phases separated inside a single mixed water/oil droplet because
water and silicone oil are immiscible4. The series of schematics and the experimental results shown
in Fig. 4C indicate the most energetically favorable configuration for water and silicone oil when
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this solution is placed on a porous CNP network material coated onto filter paper. Because the
surface energy of silicone oil is much lower than that of water, the silicone oil has a larger contact
area with air. When the silicone oil at the outer surface makes contact with the porous carbon, it is
absorbed by forming an oil meniscus. It is important to note that the color of the meniscus is light
blue, indicating that the meniscus consists of only silicone oil. After the completion of this
separation process, the oil meniscus disappeared, leaving only a water droplet on the surface.
Video S4. Porous CNP materials added to a water/hexane mixture (a) as well as a water/silicone oil
mixture (b) and the selective absorption of hexane and silicone oil from water.
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Robertson, J. Diamond-like amorphous carbon. Mater. Sci. Eng., R 37, 129-281 (2002).
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