Environmental Engineering Reference
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to make activated carbon nano fibers. These studies employed physical activation
to produce pores in precursor fibers. Compared to physical activation, the chemi-
cal activation process has important advantages, including low heat treatment
temperature, short period of processing time, large surface area and high carbon
yield; however, there has been no work reported for chemicallyactivated carbon
nanofibers from electros pun PAN. The effects of electros pinning variables,
such as applied voltage, pump flow rate and distance between the needle tip and
collector, on the resulting nanofiber diameters were studied. Mechanical prop-
erties, such as tensile, tear and burst strength, of electros pun PAN non-woven
membranes were measured and the quantitative relationships between membrane
thickness and these properties were established [93-95]. Other physical proper-
ties, such as air permeability, inter fiber pore size and porosity, were also studied.
Activated carbon nanofibers were produced from electrospun PAN by chemical
activation with potassium hydroxide (KOH) as the activating agent. They were
characterized by morphology, Fourier transforms infrared spectroscopy (FTIR),
Brunauer-Emmett-Teller (BET) surface area, total pore volume and pore size dis-
tribution. There are two processes for manufacturing the carbon nanofiber (CNF),
namely, the vapor-grown approach and the polymer spinning approach. The ac-
tivated carbon nanofiber (ACNF) is the physically or chemically activated CNF,
which have been, in many investigations, practically applied in electric double
layer capacitors, organic vapor recovery, catalyst support, hydrogen storage, and
so on. In practice, the physical activation method involves carbonizing the carbon
precursors at high temperatures and then activating CNF in an oxidizing atmo-
sphere such as carbon dioxide or steam [96, 97].
The chemical activation method involves chemically activating agents such
as alkali, alkaline earth metals, some bases such as potassium hydroxide (KOH)
and sodium hydroxide, zinc chloride, and phosphoric acid (H 3 PO 4 ). In essence,
most chemical activation on CNF used KOH to get highly porous structure and
higher specific surface area. Unfortunately, large amount of solvent were needed
to prepare the polymer solution for electros pinning and polymer blend, causing
serious environmental problem thereafter. A series of porous amorphous ACNF
were studied. Utilizing the core/shell microspheres, which were made of various
polymer, blends with solvent. In their approach, the phenol formaldehyde-derived
CNF were chemically activated by the alkaline hydroxides, and the thus-prepared
ACNF were applied as super-capacitor electrodes and hydrogen storage materials
[98-100].
In a continuous effort, some researchers proceed to investigate and compare
the various chemical activation treatments on the CNF thus prepared, with par-
ticular emphasis on the qualitative description and quantitative estimation on the
surface topology by AFM, and their relation to the microstructure of ACNF.PAN
fiber following the spinning process by several ways such as modification through
coating, impregnation with chemicals (catalytic modification) and drawing/
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