A novel type-II Bi2W2O9/g-C3N4 heterojunction with enhanced photocatalytic performance under simulated solar irradiation

In this work, the Bi2W2O9/g-C3N4 type-II heterojunction system has been prepared for the first time by an incipient impregnation method. From the results, we have stated that the addition of low amounts of Bi2W2O9 (≤5 wt%) does not provide changes in the structural and textural properties of g-C3N4, but it improves substantially the photocatalytic performance under simulated solar irradiation. The best photoactive behavior was attained in the sample with 2 wt% of Bi2W2O9, providing a removal degree of the tetracycline antibiotic about 2.6 times higher than the pristine g-C3N4. This result can be explained due to the difference in the edge positions of the valence and conduction bands of both semiconductors, which provides an efficient separation of the photogenerated charge carriers. From the study of the photocatalytic activity under several conditions, it can be inferred that the Bi2W2O9 works as a sink for the photoexcited electrons of the g-C3N4 and provides the formation of hydroxyl radicals through sequential reactions involving the superoxide ions. Furthermore, a possible photocatalytic mechanism of tetracycline removal is discussed.