Highly-efficient photocatalytic degradation of methylene blue by PoPD-modified TiO nanocomposites due to photosensitization-synergetic effect of TiO with PoPD.

Poly-o-phenylenediamine modified TiO nanocomposites were successfully synthesized via an 'in situ' oxidative polymerization method. The modified nanocomposites were characterized by BET, XRD, TEM, FT-IR, TGA, XPS, EA and UV-Vis DRS. The photocatalytic degradation of methylene blue was chosen as a model reaction to evaluate the photocatalytic activities of TiO and PoPD/TiO. The results indicated that PoPD/TiO nanocomposites exhibited good photocatalytic activity and stability. The photocatalytic activity of PoPD/TiO increased as the initial pH increased because of electrostatic adsorption between the photocatalyst and MB as well as the generation of ·OH, whereas it exhibited an earlier increasing and later decreasing trend as the concentration of the photocatalyst increased owing to the absorption of visible light. The photocatalytic stability of the PoPD/TiO nanocomposite was dependent on the stability of its structure. Based on radical trapping experiments and ESR measurements, the origin of oxidizing ability of PoPD/TiO nanocomposites on photocatalytic degradation of MB was proposed, which taking into account of ·OH and ·O were the first and second important ROS, respectively. The possible photocatalytic mechanism and photocatalytic activity enhanced mechanism has been proposed, taking into account the photosensitization effect and synergetic effect of TiO with PoPD.