Abstract:
In the present work, a widely recognized electronic material,
polyaniline (PANI) has been reported to be as an excellent surface matrix.
The PANI matrix was prepared electrochemically from an electrolytic
solution containing aniline and sulphuric acid. In order to make different
surface activity of the PANI matrix, attempt was made to treat the PANI
with aqueous solution of different pH viz., 2.47, 7.35 and 10.01 to get the
acidic-PANI, neutral-PAN I and basic-PANI matrices respectively. The
PANI that made in the presence of a dopant along with the electrolytic
medium stated above, is referred as doped-PANI.
The treated PAN I matrices were characterized using infra-red (IR)
and UV-visible spectroscopy. The IR spectral analysis of the matrices
clearly revealed that the presence of the PANI components. The UVvisible
spectra of the matrices showed characteristics interband transition
and mid-gap state as usually exhibited by PANI reported earlier. Though
the spectral feature ofIR and UV-Vis for the studied PANI matrices were
found to be identical, the SEM analysis of the matrices yielded very
significant differences in the surface morphologies of the matrices
indicating that the surface activity of the matrices could be different.
In order to examine the surface properties of the PANI matrices,
adsorption of a cationic dye, methylene blue (MB) onto the matrices was
carried out. The adsorption study showed a higher adsorption capacity for
the basic- and doped-PANI than the acidic- and neutral-PANI matrices.
The adsorption of MB onto the PANI was recorder at different time
intervals and monitored spectroscopically. The time to reach the
adsorption equilibrium was found to be within 150 min. in each matrices
at 30 DC. The adsorption data suggested a Langmuir type adsorption. In
addition, monolayer capacity and adsorption coefficients for different
PANI matrices were derived also from the adsorption data. The results
showed higher monolayer capacity and adsorption coefficients for the
basic- and doped-PANI compared to acidic- and neutral-PANI. This
result clearly suggests the superior surface activity of the basic- and
doped-PANI matrice. Indeed, the SEM analysis of the matrices also
predicted different surface morphologies of these matrices. The SEM
images predicted higher porosity of the basic- and doped-PANI compared
to that of acidic- and neutral-PANI matrices. On the other hand, the SEM
images of acidic- and neutral-PANI showed compact and uniform
morphology while those of basic- and doped-PAN I matrices were seem to
be loose, irregularly-shaped three-dimensional bodies with huge micropores
available for adsorption sites which might allowed them to yield a
higher adsorption. Furthermore, the superior adsorption capacity of basic-
PANI for the MB adsorption may also result from the electrostatic
interactions between the negatively charged basic-PANI matrix and
positively charged MB.
