Preparation and characterization of nanoparticle assisted conductive polyaniline

Abstract

In the present study, brown MnO2 nanoparticles was prepared by redox reaction of potassium permanganate with conc. ammonia solution and black MnO2 was formed by chemical coprecipitation method of potassium permanganate and manganese sulfate. Both kinds of nanoparticles were characterized by a wide range of experimental techniques including IR, EDX, X-ray, SEM and electrical conductivity. The grain size of nanoparticles was calculated from x-ray analysis and found to be 13.5 nm for amorphous black MnO2 and 14.8 nm for crystalline brown MnO2. Thus obtained MnO2 nanoparticles were successfully applied for PANI-2 polymerization of aniline and PANI/MnO2 composite preparation. The dispersion of the manganese dioxide in the polyaniline (PANI) matrix was achieved by insitu polymerization of aniline from a medium containing an oxidant ammonium peroxidisulphate, (NH4)2S2O8, oligomers and MnO2 suspension to form PANI/MnO2 composite-1. The another method for the formation of PANI/MnO2 composite-2 was the dispersion of the MnO2 nanoparticles into PANI matrix by the addition of the nanoparticles suspension to the sediment of PANI as prepared using (NH4)2S2O8 oxidant. The synthesized products PANI-2, PANI/MnO2 composite-1 and PANI/MnO2 composite-2 were compared with conventional PANI-1 as prepared using conventional oxidant (NH4)2S2O8. These substrates were characterized by UV-visible spectroscopy, Infrared (IR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) electrical conductivity and cyclic voltametry. The conductivity of PANI/MnO2 composite-1 was found about 1000 times higher than PANI-2. But PANI/MnO2 composite-2 has conductivity, 10 times less than PANI-2. This is due to the dispersion of MnO2 nanoparticles into the polymer matrix by following two different ways. From X-ray, it was observed that PANI-1, PANI-2 and PANI/MnO2 composite -1 were amorphous in nature but PANI/MnO2 composite-2 has both amorphous and crystalline nature. The distinct synthetic mode may be responsible behind this. The amounts of MB adsorbed on PANI/MnO2 composite and PANI-2 were higher than that of PANI-1 due to increased surface area. The adsorption of MB on PANI-2 and PANI/MnO2 composite-1was higher at pH 9.2 which is due to the dedoped negatively charged PANI matrices. The monolayer capacity (χm) of PANI-2 was found to be comparatively less than the PANI /MnO2 composite -1. The monolayer capacity of PANI-2 and PANI/MnO2 composite-1 were 2.4 and 3.99 mg-1 respectively. The surface area of PANI-2 was found to be 5.28 m2g-1 in 130 Å BET with N2 and 3.17 m2g-1 in 78 Å BET with Ar. These values were found to be comparatively less than that of PANI/MnO2 composite - 1 for which the surface areas were found to be 8.78 m2 g-1 in 130 Å BET with N2 and 5.27 m2 g-1 in 78 Å BET with Ar. The adsorption capacity (KL) for PANI-2 and PANI/MnO2 composite-1 were found to be 1.43×106 L mole-1 and 3.01×106 L mole-1 respectively. The surface area as a consequence of adsorption of the MB dye appears to be emphasized due to the electrostatic interaction between the ionic dye adsorbate and the charged PANI adsorbent. The degradation of dyes (MB&OG) on MnO2 were also examined. The degradation of MB on MnO2 occurs at a significant rate irrespective of the pH. This is due to the electrostatic attraction of cationic dye and negative surface at lower pH (pHPZC = 8.53) and MnO2 becomes very reactive at lower pH. But degradation of anionic dye OG on MnO2 was higher at pH lower than pHPZC due to the electrostatic attraction between anionic dye and positive surface charge. However it was found that the rate of degradation of MB was faster than that of OG on MnO2. The capacity of MnO2 for MB and OG degradation was found to be 103.2 and 167.5 mg/g respectively.