Photocatalytic degradation of organic dyes by the conjugated polymer poly(1,3,4-oxadiazole)s and its photocatalytic mechanism

A donor–acceptor conjugated polymer, poly(1,3,4-oxadiazole)s (POD), was synthesized by a one-step polycondensation in oleum and spun into filaments using wet-spinning. The structure of POD was confirmed and characterized by FTIR, TG, elemental analysis, and UV–Vis spectroscopies. FTIR and elemental analysis proved the successful synthesis of POD, and TG showed the high thermal stability of POD. The UV–Vis spectra showed that POD absorbed almost all ultraviolet ranging from 200 to 400 nm, but it did not absorb the visible light. Considering the conjugated structure of POD and the dearth of research regarding its photocatalytic ability, studies were carried out on the photocatalytic performance of the POD for the photocatalytic degradation of methyl orange, methylene blue, and reactive brilliant blue. The results showed that POD was an effective photocatalyst to destroy the three types of dyes mentioned above. The photocatalytic mechanism of POD was also studied in this work. The superoxide anion radical (\( {\text{O}}_{2}^{\cdot - } \)) was detected by nitrotetrazolium blue chloride (NBT) method and was believed to play a key role in photodegradation of dyes. Moreover, it was also found that ·OH, which was generated from \( {\text{O}}_{2}^{\cdot - } \) by the addition of H⁺, was the main reason for the rapid degradation of the dyes. Finally, the reusability of POD as the photocatalyst was also investigated. The results indicated that the reusability of POD gradually decreased after 80 min of continuous irradiation, which might be attributed to the relatively poor photostability of POD itself.