Retrieval of Fluoride Using Polyaniline Polypyrrole Composite

Abstract

This paper explains the possible use fo Polyaniline polypyrrole composite (PANi/PPy) as an adsorbent for the removal of the fluoride ions, from aqueous solution. The adsorption of the fluoride was appreciable around the natural pH of the aqueous solution of fluoride ions. This shows that adsorption of the fluoride ions could be carried out on the PANi/PPy composite without adjusting the pH of the medium. The experimental data yielded perfect fits with Freundlich isotherm equation. The values of the adsorption coefficients computed from the isotherms indicated the potential of the adsorbent for practical applications in defluoridation processes. Adsorption kinetics obeyed a first-order kinetic model. Diffusion of the fluoride ions into the micro pores and macro pores is the rate-determining step in the mechanism of the adsorption process. The adsorption of fluoride ions on the PANi/PPy composite was non-spontaneous and endothermic in nature with the defluoridation capacity increasing with increasing temperature due to increase in the rate of adsorption.The enthalpy change for the adsorption process was in the range of 25-67 kJ mol-1, which did not, indicates very strong chemical forces between the adsorbed fluoride ion and the PANi/PPy composite surface. This observation was well supported by the XRD pattern studies. Hence, physisorption seems to be the major mode of adsorption.