Developing high-efficiency π conjugated polymer semiconductor for photocatalytic degradation of dyes under visible light irradiation

Abstract

In this study, a series of conjugated polyimide (PI) photocatalysts were prepared via a facile thermal condensation of melamine and various aromatic dianhydride monomers. The samples were characterized by Fourier transform infrared spectroscopy, elemental analysis, X-ray powder diffraction and UV-vis diffuse reflectance spectroscopy. All samples showed a well-developed polyimide structure and strong visible-light absorption. The electronic band structures of PI were simulated by density functional theory calculations. Photocatalytic results showed that the PI with a best coplanar conformation in the backbone and strongest photooxidative capability exhibited the highest activity for methyl orange (MO) degradation. In addition, it displayed an excellent stability during four cycles of photocatalytic testing. Photocatalytic mechanism study indicated that photogenerated holes rather than electrons play a crucial role on the photodegradation of MO. Moreover, the participation of reactive oxygen species such as OH˙, O₂˙⁻ and ¹O₂ was examined by adding corresponding scavengers. However, only ¹O₂ was identified as the active species involved in the MO degradation. This work represents the great potential of metal-free PI photocatalyst as sustainable, efficient and low-cost material for environmental remediation and solar energy conversion.