Photo-Fenton and oxygen vacancies' synergy for enhancing catalytic activity with S-scheme FeS2/Bi2WO6 heterostructure

Abstract

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.