Synthesis and characterization of polyaniline, polypyrrole and zero-valent iron-based materials for the adsorptive and oxidative removal of bisphenol-A from aqueous solution

One pot synthesis of a polypyrrole, polyaniline and Fe⁰ nano-composite (Fe⁰-PPY/PANI) was achieved by polymerizing aniline and pyrrole with FeCl₃ followed by the reduction of Fe³⁺ to Fe⁰ with NaBH₄. PPY/PANI was synthesized the same way as Fe⁰-PPY/PANI, except that all the FeCl₃ was removed by rinsing. The presence of Fe⁰ was demonstrated using several analytical techniques; this was shown in comparison to materials that are without Fe⁰. A series of materials were screened as both adsorbents and catalyst for the activation of H₂O₂ towards bisphenol A (BPA) removal in batch experiments. Polymers performed better than composites containing Fe⁰ at adsorption, whereas Fe⁰ based materials were better catalysts for the activation of H₂O₂. BPA samples were then spiked with other contaminants including sewage water to test the performance of the various adsorbents and Fenton catalysts. PPY/PANI was found to be a better adsorbent than the rest, whereas Fe⁰-PPY/PANI was the best Fenton catalyst. The adsorption kinetics of BPA onto PPY/PANI was studied; it was found that the process was governed by the pseudo-second-order kinetic model. The adsorption isotherms revealed that the amount of BPA taken up by PPY/PANI increased with increasing temperature and was governed by the Langmuir adsorption isotherm. The mechanism in which Fe⁰-PPY/PANI and H₂O₂ degraded BPA was studied, it was found that surface-bound hydroxyl radicals were responsible for the degradation of BPA. It was also shown that the degradation process included the formation of smaller compounds leading to the reduction of the total organic content by 57%.