Environmental Engineering Reference
In-Depth Information
acrylonitrile was used as a source of carbon. From the results, it was observed that
dye adsorption equilibrium time for CNTs/ACF is shorter as compared to ACF
and monolayer adsorption capacity does not display a linear increase with in-
creasing the BET surface area. The decoration of CNTs tends to lower the poros-
ity of the ACF. This finding indicates that the total microporosity of ACF cannot
be fully accessed by the dye molecules. However, as-produced CNTs offer more
attractive sites, including grooves between adjacent tubes on the perimeter of the
bundles, accessible interstitial channels, and external nanotube walls. Therefore,
the appearance of CNTs plays a positive role in (i) facilitating the pore accessi-
bility to adsorbates and (ii) providing more adsorptive sites for the liquid-phase
adsorption. This reflects that CNTs/ACF contains a large number of mesopore
channels, thus preventing the pore blockage from the diffusion path of micropores
for adsorbates to penetrate [72].
A novel technique was performed to grow high-density carbon nanotubes
(CNTs) that attach to PAN-based ACFs. Such unique nano/microscaled carbon
composites can serve as an excellent electrode material of EDLCs. The existence
of CNTs is believed to play two important roles in enhancing the performance of
EDLCs: (i) since its has good electric conductivity, the presence of CNTs would
promote the contact electron transfer or lower contact resistance between the cur-
rent collector and the carbon composite;(ii) CNTs not only provide additional
exterior surface area for double-layer formation but also shift from micropore
size distribution to mesopore size distribution that may reduce ionic transfer re-
sistance and improve the high rated is charge capability. It is generally recognized
that transition metals (Fe, Co, and Ni) can serve as catalytic sites in inducing
carbon deposition, thus forming CNTs. This reveals that the uniform dispersion
of the “seeds” on ACF surface, followed by a catalytic chemical vapor deposi-
tion (CCVD) treatment, would offer a possibility to fabricate the unique nano/mi-
croscaled carbon composites. The mesoporous channels, which came from CNT
branches, would provide available porosity that is accessible for ionic transport
and energy storage. This work intends to investigate the applicability of using
the carbon composite as an electrode material for EDLCs. Two configurations
(with and without CNTs) have been compared with respect to their double-layer
capacitances and high-rate capability, analyzed by cyclic voltammetry (CV) and
charge-discharge cycling. This work has demonstrated that the specific capaci-
tance and high-rate capability of PAN-based ACF in H 2 SO 4 can be enhanced with
the decoration of CNTs. A CVD technique enabled to catalytically grow CNTs
onto ACF, thus forming CNT-ACF composite. N 2 physisorption indicated that the
mesopore fraction of ACF is found to increase after the growth of nanotubes. The
specific double-layer capacitance and high-rate capability were significantly en-
hanced because of the presence of nanotubes. The distributed capacitance effect
and inner resistance were significantly improved for the CNT-ACF capacitor.
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