Photodegradation of methylene blue by photocatalyst of D-A-D type polymer/functionalized multi-walled carbon nanotubes composite under visible-light irradiation.

A donor-acceptor-donor (D-A-D) type monomer (3,6-bis(2-(3,4-ethylenedioxy- thiophene))pyridazine) (EPE) with pyridazine as intermediate unit (acceptor) and 3,4-ethylenedioxythiophene (EDOT) as sealing unit (donor) was successfully synthesized. The functionalized multi-walled carbon nanotubes (f-MWCNT) was covalently linked with polymer chain via chemical oxidative polymerization of monomer EPE to form poly(EPE)/f-MWCNT composite. The prepared composite was characterized by Fourier transform infrared spectroscopy (FT-IR), Ultraviolet-visible absorption spectra (UV-vis), X-ray diffraction (XRD), Energy-dispersive X-ray spectroscopy (EDS), and Field emission scanning electron microscope (FESEM), respectively. The photocatalytic activity of poly(EPE)/f-MWCNT was investigated toward degrading methylene blue (MB) dye solution (1 × 10(-5) M) under visible light irradiation. As expected, the degradation efficiency of poly(EPE)/f-MWCNT is significantly higher than that of either pure poly(EPE) or poly(EPE)/MWCNT for MB dye, especially the kinetic constant of poly(EPE)/f-MWCNT is more than 6 times of poly(EPE)/MWCNT. Besides, the reactive oxygen species trapping experiments indicate that the degradation of MB over the poly(EPE)/f-MWCNT composite mainly results from holes oxidation. Moreover, the enhancement of the photodegradation rate is mainly attributed to the superior stability, strong light absorption ability, and highly effective photo-generated electron-hole pairs of the poly(EPE)/f-MWCNT composite. A reasonable mechanism for the enhanced reactivity was proposed.