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%.

Resin-gel incorporation of high concentrations of W6+ and Zn2+ into TiO2-anatase crystal to form quaternary mixed-metal oxides: effect on the a lattice parameter and photodegradation efficiency.

The search for a viable photocatalyst for water remediation is ongoing and in recent times the efforts have predominantly focused on improving the limitations of the TiO2 photocatalyst. This paper reports a dual strategy for improving the photocatalytic properties of TiO2. The first strategy is to dope up to 30% of W6+ and Zn2+ into the crystal lattice of TiO2 using the resin gel technique to synthesize quaternary mixed metal oxides (QMMOs). It was demonstrated by laser Raman spectroscopy, PXRD and various other strategies, including dislodging the dopants from the crystal lattice of TiO2, that these materials were successfully synthesized. More importantly, UV-DRS showed that these materials could absorb visible light. TiO2 and the QMMOs were also supported on 10% NCNTs synthesized from coal fly ash, by slightly modifying the resin gel technique. It was observed from TEM images that the NCNTs were uniformly coated with TiO2 and QMMO nanoparticles. These composites were observed to have lower photoluminescence emission spectra when compared to neat TiO2 and unsupported QMMOs. The two-part strategy employed in this project worked as the QMMOs supported on 10% NCNTs had higher visible light photodegradation efficiencies compared to neat TiO2 and the unsupported QMMOs.