BASIC CONCEPTS AND AN OVERVIEW - Foundations of Nanotechnology: Pore Size in Carbon-Based Nano-Adsorbents - page 36

give a paper like composite. 90 wt.%-99 wt.% of AC was first incorporated into
the CNT pulp, and the deposited on a filter to make composites [72].
The specific surface area, pore volume and pore size distribution are also the
important factors affecting the electrochemical performance of super-capacitors.
The N 2 adsorption isotherms and pore size distributions of AC powder and CNTs
are studied. The quantitative data extracted from the N 2 adsorption isotherms are
given. AC presents a type-Ⅰ isotherm, which is typical for a microporous mate-
rial. The BET surface area and average pore diameter of AC powder were 1374
m 2 /g and 2.35 nm, respectively. After the addition of AC or CNTs, the N 2 ad-
sorption was almost unmodified in the small relative pressure region correspond-
ing to micropores, whereas a noticeable enhancement at P/P 0 > 0.9, in the range
of mesoporosity, was observed. The pore size distribution of CNTs showed two
peaks at about 2.5 and 20 nm. The former may arise from the inner space of
CNTs and the latter probably arise from the pores between CNTs. The pore size
distribution of AC-CNT-5% also showed two small peaks at about 10 and 25 nm.
The former may be generated by the pores in bundles of CNTs formed during the
liquid phase process. The latter results from the pores generated by the stacking
of CNTs, and its size was slightly increased due to the presence of AC particles.
The BET surface area and average pore diameter of AC/AB were 1011 m 2 /g and
2.64 nm. The total pore volume decreased due to the addition of 15 wt.% AB and
10 wt.% PTFE. However, the ratio between the mesoporous and microporous
volumes (Vmeso /Vmicro) was almost the same. The BET surface area and aver-
age pore diameter of AC-CNT-5% were 1223 m 2 /g and 2.99 nm. The micropore
volume of the AC was slightly diminished by the presence of CNTs, whereas the
mesoporous volume increased from 0.32 to 0.38 cm 3 /g. The Vmeso/Vmicro ratio
showed a significant increase.
1.1.6.7 CNT-FIBER COMPOSITES AS ADSORBENT
1.1.6.7.1 CNT-BASED FIBERS
For many applications, fibrous materials are more suitable than bulk materials. In
addition, fiber production techniques tend to be suited for the alignment of nano-
tubes within the polymer matrix. The researchers observed that the alignment of
nanotubes within the composite fiber was improved dramatically by increasing
the draw ratio. Many subsequent studies also showed that the mechanical/electri-
cal properties of these composite materials are greatly enhanced by fiber spinning.
A part from the traditional melt spinning methods, composite fibers can also be
produced by solution-based processing. The coagulation-spinning method was
designed so that the CNTs were attached to each other while they were oriented
in a preferential direction by a given flow. Nanotube aggregation was obtained
by injecting the CNT dispersion into a rotating aqueous bath of PVA, such that
nanotube and PVA dispersions flowed in the same direction at the point of injec-
tion. Due to the tendency of the polymer chains to replace surfactant molecules