Photo-Fenton and oxygen vacancies' synergy for enhancing catalytic activity with S-scheme FeS2/Bi2WO6 heterostructure†
Using calcination and solvothermal methods, a series of FeS2/Bi2WO6 heterojunctions were prepared by coupling FeS2 into the surface oxygen vacancy enriched Bi2WO6. The prepared catalysts were used as photo-Fenton catalysts to degrade tetracycline hydrochloride (TC-HCl) and rhodamine B (RhB). Then, a rational catalytic mechanism where an S-scheme catalyst was constructed between FeS2 and Bi2WO6-OVs was put forward. Furthermore, electron spin resonance (ESR) was employed to confirm that the main active substances in the photo-Fenton degradation process are hydroxyl radicals (˙OH) and superoxide radicals (˙O2−). The enhancement of catalytic activity is mainly due to the synergistic effect between photocatalytic oxidation and Fenton oxidation. And the introduction of oxygen vacancies can not only broaden the light absorption range of the catalyst because of the rise of the valence band but also promote the efficient separation of photogenerated carriers. Besides, the O–O bond of H2O2 could be elongated and weakened due to the presence of surface oxygen vacancies, which can promote the decomposition of H2O2. Meanwhile, the photogenerated electrons in the conduction band (CB) of Bi2WO6-OVs can rapidly transfer to FeS2 near the oxygen vacancies on the catalyst surface, which can achieve a cyclic process from Fe3+ to Fe2+ and boost the degradation efficiency of traditional Fenton catalysis and photocatalysis. The experimental results showed the photo-Fenton rate constants for TC-HCl and RhB over 1%FeS2/Bi2WO6 which were evaluated to be about 0.04430 and 0.02007 min−1 within 50 and 150 min, which was 1.74 and 1.41 times that of the optimum Fenton process, respectively. This strategy showed that the FeS2/Bi2WO6 heterostructure has great advantages in photo-Fenton treatment of multiple organic pollutants due to the synergy of photocatalysis and Fenton catalysis.