In situ preparation of p-n BiOI@Bi5O7I heterojunction for enhanced PFOA photocatalytic degradation under simulated solar light irradiation

The strong persistence, wide presence and potential toxicities of perfluorooctanoic acid (PFOA) in aquatic environment makes it a challenge to develop advanced technologies to eliminate it from water. In this study, novel BiOI@Bi5O7I p-n heterojunction photocatalysts were facilely prepared by calcinating BiOI at 350 degrees C < T < 410 degrees C. Under simulated solar light irradiation, the degradation rate constant (k = 0.247 h(-1)) of PFOA by the BiOI@Bi5O7I heterojunction prepared at 390 degrees C (T-390) was four times of that by pristine BiOI (k = 0.061 h(-1)) and 1.2 times of that by Bi5O7I (prepared at 410 degrees C, k = 0.206 h(-1)). T-390 also exhibited excellent mineralization efficiency by removing about 60% of total organic carbon in 6 h of irradiation. The significantly enhanced photocatalytic activity of BiOI@Bi5O7I composite was mainly attributed by the unique band gap structure of the p-n heterojunction, which enhanced the visible-light absorbance and accelerated the separation of photogenerated charge carriers. The generated intermediate products were analyzed by ultra-performance liquid chromatography-mass spectrometry, and the results indicated that PFOA was decomposed by stepwise losing CF2 units. The BiOI@Bi5O7I heterojunction also possessed very good durability and reusability, displaying a great potential in PFOA containing water treatment.