Defect engineering in conjugated polyimides for promoting visible-light-driven photocatalytic benzylamine oxidation

Defect engineering is a promising strategy that essentially tailors the specific surface area, energy band structure and photocatalytic properties of catalysts. Herein, a series of oxygen defect modified polyimides (PI-NaHCO3 (1 : 1, 1 : 4, and 1 : 8)) containing triazine rings have been synthesized via thermal polymerization by introducing an inorganic foaming agent NaHCO3 into the synthesis of classical polyimide (PI). During the polymerization and washing process, a large amount of gas generated by NaHCO3 breaks the imide bond connections in PI, resulting in the formation of oxygen defects. The experimental results revealed that with the introduction of oxygen defects, the band gap of PI broadened, and the absorption band edge exhibited a certain blue shift. However, the separation and transmission of photogenerated carriers were significantly enhanced, and the radiation recombination has been inhibited. Therefore, the photocatalytic activity of samples was significantly improved. Among them, PI-NaHCO3 (1 : 4) shows the optimal catalytic activity in photocatalytic benzylamine oxidation and photocatalytic hydrogen evolution experiments. Under irradiation using a 420 nm LED (10 W), the conversion and selectivity of benzylamine to corresponding imine are more than 99%. This work provides a new way for the design of defective polyimide materials.