Visible-light-induced photocatalytic degradation of methylene blue with polyaniline-sensitized TiO2 composite photocatalysts

A series of polyaniline (PANI)-sensitized TiO2 composite photocatalysts (PANI/TiO2) with different mass ratio of polyaniline to nano- TiO2 (P25) (1:200–1:700) were facilely prepared by mixing a tetrahydrofuran (THF) solution of camphorsulfonic acid (CSA)-doped polyaniline (PANI-CSA) and TiO2 nanoparticle suspension in ethanol. Transmission electron microscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and ultraviolet–visible diffuse reflectance spectroscopy (DRS) measurements were used to characterize the resulting composite photocatalysts, and their photocatalytic activities were investigated by degrading methylene blue (MB) under visible-light irradiation (λ>400nm). The results showed that the surface polyaniline sensitization had no effect on the crystalline structure but aggravated the agglomeration of TiO2 nanoparticles by forming multi-particles. After being sensitized by PANI, the light response of TiO2 was extended to visible-light regions and the photocatalytic activity of the composite photocatalysts was enhanced. MB could be degraded more efficiently on PANI/TiO2 than on the bare TiO2 when the mass ratio of polyaniline to TiO2 was in the range 1:400–1:700, and the optimum sensitized effect was found at a mass ratio of 1:500. The determined rate constant of MB degradation over PANI/TiO2 (1:500) was 0.01515 min−1, which is 1.57 times higher than that of bare TiO2 (0.00963 min−1). Furthermore, PANI/TiO2 composite photocatalysts showed good photocatalytic stability after five runs under visible light. The enhancement of photocatalytic activity of the composite photocatalysts could be attributed to the sensitizing effect of PANI. A possible mechanism for the photocatalytic degradation of methylene blue is also proposed.