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

Abstract

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%.

Fig. 1. The PXRD patterns of the various materials.

Fig. 2. TEM images of (a) Fe⁰-PANI, (b) Fe⁰-PPY, (c) Fe⁰-PPY/PANI (d) particle size distribution of Fe⁰ nanoparticles in Fe⁰-PPY/PANI and SEM image of (e) PPY/PANI and (f) Fe⁰-PPY/PANI.

Fig. 3. Thermogram of (a) PPY/PANI and (b) Fe⁰-PPY/PANI.

Fig. 4. Effect of pH on the (a) adsorption of BPA using PPY and (b) Fenton degradation of BPA using Fe⁰. Experimental conditions: 50 ml of 50 ppm BPA, 25 mg of catalyst or adsorbent and 15 ppm H₂O₂ for only Fenton reactions.

Fig. 5. Removal efficiencies of BPA using the various materials by (a) adsorption and (b) Fenton reaction. Experimental conditions: 50 ml of 50 ppm BPA, 25 mg of catalyst or adsorbent and 15 ppm H₂O₂ for only Fenton reactions.

Fig. 6. Removal efficiencies of bisphenol-A in the presence of other contaminants using the various materials by (a) adsorption and (b) Fenton reaction. Experimental conditions: 50 ml of 50 ppm BPA, 25 mg of catalyst or adsorbent and 15 ppm H₂O₂ for only Fenton reactions.

Fig. 7. Removal efficiencies of bisphenol-A and TOC using various materials by (a) adsorption and (b) Fenton reaction. Experimental conditions: 200 ml of 50 ppm BPA, pH 6 for adsorption experiments and pH 3 for Fenton reactions, 100 mg of adsorbent or Fenton catalyst and 25% of sewage-water.

Fig. 8. Adsorption kinetics and the pseudo-second-order kinetic plot of BPA adsorption onto 50 mg of PPY/PANI. Experimental conditions: 200 ml of various concentrations of BPA (50, 75 and 100 ppm) at pH 6.0 and at 23 °C.

Fig. 9. Diffusion models showing (a) interparticle and (b) intraparticle. Experiments conditions: 200 ml of various concentrations of BPA (50, 75 and 100 ppm) at pH 6.0 and at 23 °C adsorbed onto 50 mg of PPY/PANI.

Fig. 10. Effect of solution temperature on the removal of BPA using PPY/PANI where the temperature is varied from 298 to 318 K. Experimental conditions: 200 ml of 50 ppm BPA and 100 mg PPY/PANI.

Fig. 11. Effect of methanol and potassium iodide on the removal of BPA. Experimental conditions: 200 ml of 50 ppm BPA at pH 6 with 100 mg Fe⁰-PPY/PANI and 5 mM KI or 350 mM methanol.

Fig. 12. Chromatograms of the aliquots sampled at (a) 0 min, (b) 30 min, (c) 180 min and (d) is the MS spectrum of the aliquot sample at 180 min. Experimental conditions: 200 ml of 50 ppm BPA at pH 6 with 100 mg Fe⁰-PPY/PANI.

Fig. 13. Advanced Fenton reaction mechanism for the degradation of BPA using Fe⁰-PPY/PANI.