Abstract:
Apart from the use of conducting polyaniline as electronic
materials, in the present work, neutral and charged polyaniline are
utilized as the effective adsorbents for their possible application
in removing organic dyestuff, such as methylene blue, procion red
and inorganic species, viz., nickel chloride from their aqueous
solutions.
1
•
charged while the other two matrices seem to be either neutral
or negatively charged.
UV-Vis and IR spectroscopy studies yielded useful
qualitative information on the treated polymer matrices. The
strong absorption maxima observed in the ultraviolet region may
be attributed to the inter band transition; the other intense band
in the visible region probably results from the transition between
the mid-gap states. From the IR spectra, band characteristics
confirmed the differences between the treated polyaniline
matrices. The electrical conductivity measurements also provide
strong evidence regarding the difference of the electrical
properties of the treated polymer. The acid treated polymer
shows a conductivity of "'1 Scm-I while the distilled water and
base treated samples show conductivity of 10-6 and 10-7 Scm-I,
respectively.
Surface morphology obtained by SEM provides very
interesting results. The acid treated polyaniline seems to consist
of agglomerates and stacked over the surface to make a big
deposit. On the other hand, distilled water and base treated
matrices show granular morphologies. The grain aggregates to a
short-pillar like body in the morphology of distilled water treated
2
polyaniline while in the base treated one, the grains are collected
to a body like a broken brick-shaped showing definite size and
sharp edges.
The polyaniline matrices thus treated were used as
adsorbent and found to be adsorbed the dyestuffs, methylene
blue and procion red from their aqueous solutions at various pH.
The removal of dyes was monitored spectroscopically by
measuring the change of absorbance at their corresponding ""max.
The molar absorption co-efficients of methylene blue and procion
red were found to be 59600 L mol-! cm-! at 661 nm and 8518 L
mol-! cm-! at 535 nm, respectively. The cationic dye, methylene
blue shows a significant adsorption on the base treated
polyaniline (negatively charged), while procion red, a negative dye,
found to be adsorbed preferentially on the positively charged
acid treated polymer. The adsorption isotherms for both
methylene blue and procion red seem to follow Langmuir isotherm.
However, the inorganic salt, nickel chloride adsorption seems to
be very low both on neutral and charged polyaniline matrices
suggesting a different mechanism for the adsorption on the
polymeric matrices employed.
