TiO₂/polypyrrole nanocomposites photoactive under visible light synthesized by heterophase polymerization in the presence of different surfactants

TiO₂/polypyrrole nanocomposites were synthesized by batch (B) and semi-batch (SB) heterophase polymerization of pyrrole onto TiO₂ nanoparticles. Sodium bis-2-ethylhexyl sulfosuccinate (AOT), hexadecyltrimethylammonium bromide (CTAB), and sodium dodecyl sulfate (SDS) were used as surfactants while ammonium persulfate served as oxidizing agent. The resulting nanocomposites were analyzed by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, energy dispersive X-ray spectroscopy, UV/Vis diffuse reflectance spectroscopy, Raman spectroscopy, and cyclic voltammetry. TiO₂/polypyrrole nanoparticles were tested as photocatalysts under visible light in the degradation of methylene blue. Nanocomposites with conductivities between 4.85 × 10^-7 and 1.88 × 10^-2 S/cm were obtained. It was concluded that the polymerization mode and the surfactant type, used as a stabilizing agent, have a strong effect on the photocatalytic activity of the materials. The best results were obtained when SDS was used and polymerization carried out in SB mode. Percentage of photodegradation under visible light after 15 min was as follows: TiO₂ 1.7 %, CTAB-SB 25.5 %, SDS-B 39.6 %, CTAB-B 57.5 %, AOT-SB 69.4 %, AOT-B 80.1 %, and SDS-SB 94.1 %; while under UV light irradiation after 60 min the percentages were: SDS-B 64 %, CTAB-SB 67 %, CTAB-B 69 %, TiO₂ 71 %, AOT-SB 88.2 %, AOT-B 95.0 %, and SDS-SB 96.5 %.