STUDIES ON POLYANILINE AS ADSORBENT FOR DYE REMOVAL

Abstract

Dyes are one of the major groups of water polluting chemicals among all water pollutants. Effluent from the textile industries contribute a huge amount of dyes which are not only highly toxic, but are also a matter of concern due to aesthetic point of view. They reduce the sun light penetration and photosynthesis, thereby increasing the biological oxygen demand and causing lack of dissolved oxygen that is vital to sustain aquatic life. The removal of the colouring materials and dyes from the effluent of textile industries is an extremely demanding task because pigments and dyes confront biodegradation and remains in the environment for long span of time. In spite of the primary recognition of polyaniline as a conducting polymer, it is now emerging as an adsorbent for the removal of dyes. This is due to its improved properties such as larger surface area, modified mechanical properties, low cost, high adsorption capacity, and ease of synthesis and exclusive oxidation/reduction and acid/base doping/de-doping chemistry. In the present studies, polyaniline (PANI) nanofibers (salt and base forms) were synthesised by using the interfacial polymerization method and further used as adsorbent for the eradication of different dyes from their aqueous solutions. The synthesized adsorbent was characterized by SEM, HRTEM, XRD, Zeta potential, BET and FTIR techniques. From morphology characterization (SEM and HRTEM) the size of the nanofibers was found to be 60 nm and XRD spectrum shows the amorphous nature of polyaniline with a little bit crystalline portion. Zeta potential testing indicated the positive charge on the salt form of polyaniline with positive value of zeta potential equal to10.1 mV. The UV- visible spectroscopy was used to analyze the un-adsorbed amount of the dyes. The kinetics of the adsorption of different dyes was studied using reported kinetic models such as Pseudo-first-order, Pseudo-second-order and Intra-particle diffusion models. In addition, the Langmuir and Freundlich isotherm models were also studied to analyze the equilibrium data. The effects of different parameters such as contact time, initial dye concentration and pH were also studied. It has been seen that approx 95% methyl orange (MO)

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and 67% of methylene blue (MB) dye was removed by using salt form of polyaniline respectively and approx 91% of MB dye was removed by using base form of polyaniline at optimum conditions of adsorption parameters. Also, the investigation was carried out on structurically modified PANI nanofibers, modified by doping with phytic acid (PA) used to study the adsorption of methylene blue dye from aqueous solution. The doped adsorbent possessed negative charge on its surface with negative value of zeta potential equal to -2.06 mV. Approx 96% of methylene blue dye was removed by using doped polyaniline. The desorption study was also carried out to regenerate the exhausted polyaniline. Approx 86% of MB dye was recovered by using 95% ethanol solution in case of polyaniline base form and approx 65% of MB dye was recovered in case of PA doped PANI. Evidently, the PANI nanofibers are reported to be a novel adsorbent for removal of dyes.