Activated Carbon Fibers
with a High Heteroatom Content
by Chemical Activation of PBO with Phosphoric Acid
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Abstract
The preparation of activated carbon fibers (ACFs) by
phosphoric
acid activation of poly(<i>p</i>-phenylene benzobisoxazole)
(PBO) fibers was studied, with particular attention to the effects
of impregnation ratio and carbonization temperature on porous texture.
Phosphoric acid has a strong effect on PBO degradation, lowering the
temperature range at which the decomposition takes place and changing
the number of mass loss steps. Chemical analysis results indicated
that activation with phosphoric acid increases the concentration of
oxygenated surface groups; the resulting materials also exhibiting
high nitrogen content. ACFs are obtained with extremely high yields;
they have well-developed porosity restricted to the micropore and
narrow mesopore range and with a significant concentration of phosphorus
incorporated homogeneously in the form of functional groups. An increase
in the impregnation ratio leads to increases in both pore volume and
pore size, maximum values of surface area (1250 m<sup>2</sup>/g) and
total pore volume (0.67 cm<sup>3</sup>/g) being attained at the highest
impregnation ratio (210 wt % H<sub>3</sub>PO<sub>4</sub>) and lowest
activation temperature (650 °C) used; the corresponding yield
was as large as 83 wt %. The obtained surface areas and pore volumes
were higher than those achieved in previous works by physical activation
with CO<sub>2</sub> of PBO chars