Hen Feather: A Remarkable Adsorbent for Dye Removal - Green Chemistry for Dyes Removal from Wastewater - page 418

classify birds as those living beings which carry feathers at some point in
their life span. Feathers possess marvelous and proficient structures. They
are flexible but at the same time strong [63]. They help keep birds warm
and dry in winter, yet help them to keep cool and hold and transport water
during scorching summer weather. Apart from assisting birds to fly, feath-
ers keep them protected from injury, and allow them to send signals to
their friends and warnings to their enemies.
Feathers are composed of keratin. Chemically keratin is similar to the
substance that makes up the fur of most mammals, scales of reptiles, horns
of animals like rhinoceros and fingernails of humans [64]. Though feathers
come in several forms, they are all made up of the same basic parts. These
parts may be absent or rearranged a bit, depending on the main function
of the feather. Every feather possesses a main shaft, which is also known as
rachis. This shaft or rachis supports the entire structure of the feather. The
shaft has blood vessels within it. During the growth of the feather, these
blood vessels help in carrying nutrients to the growing parts of the feather.
On maturity, these blood vessels die out and the rachis is sealed at the base,
leaving the feather shaft hollow. Because of this phenomenon the feather is
very light in weight [65].
Branching off the rachis are barbs; barbs are branched into barbules, and
the barbules have branches called barbicels. Thus, these three parts—barbs,
barbules and barbicels—give the feather its “feather-like” shape. Barbicels
are very tiny, and a good magnifying glass or microscope is needed to
observe them. They are generally hook-shaped, and interweave with each
other [65]. They hold the vane of the feather together in a similar man-
ner as Velcro strips. If you've rubbed a feather the “wrong way” and then
smoothed it back to its original shape, what you've done is un-hook and
re-hook the barbicels. The barbicels can hold the feather vanes together so
tightly that water cannot go through.
A survey of literature reveals that the use of hen feathers as a candidate
for potential adsorbent for the removal of hazardous dyes was an innovative
initiative first created in a laboratory in the year 2006 [17-26]. Before the
year 2006, the use of hen feathers as adsorbent was limited to the removal
of metal ions only and Al-Asheh and coworkers [66-68] were the major
contributors in this area. In a similar type of study [68] binary systems of
copper, zinc and nickel ions have been removed through batch adsorp-
tion processes using chicken feathers as an adsorbent. Teixeira et al. [69]
described a biological route for direct sorption of aqueous As (III) species
over a waste biomass with a high fibrous protein content obtained from
chicken feathers. In recent years attempts have been made to use chemi-
cally modified feathers for the removal of heavy metal (Zn 2+ ) from polluted