Modification of polyaniline surface by electrochemical means and study of adsorption on the modified surface

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.