Conducting polymer/alumina composites as viable adsorbents for the removal of fluoride ions from aqueous solution

The polyaniline/alumina (PANi–AlO) and polypyrrole/alumina (PPy–AlO) composites were prepared and characterized by FT-IR, SEM and X-ray diffraction studies and were employed as adsorbents for the removal of fluoride ions from aqueous solution by the batch sorption method. The amount of fluoride ions adsorbed per unit mass of the adsorbents was observed to be higher than that by the individual constituents. The maximal amount of adsorption is 6.6 mg/g for PANi–AlO and for PPy–AlO it is 8 mg/g. The Langmuir and Freundlich isotherms were used to describe adsorption equilibrium. The kinetics of the adsorption process was investigated using Natarajan–Khalaf equation and intraparticle diffusion model. FT-IR and XRD pattern of the adsorbent, before and after the adsorption is recorded to get better insight into the mechanism of the adsorption process. The results of equilibrium and spectral investigations revealed that the mechanism of fluoride ion removal by these composites involve both the formation of aluminium–fluoro complexes on the alumina surface and doping/dopant-exchange of fluoride ions in the polymer.