Construction of novel Bi ₂ S ₃ @Zn-Co-cLDHs heterojunction for enhanced photocatalytic degradation of levofloxacin with persulfate activation under visible light: mechanism and degradation pathway

This study effectively synthesized the novel Bi₂S₃@Zn-Co calcined layered double hydroxides heterojunction (Bi₂S₃@ZC-cLDHs) <i>via</i> co-precipitation and thermal methods. ZC-LDHs built with a Zn²⁺/Co²⁺ molar ratio of 3 : 1, after calcination at 600 °C, yielded a blend of ZnO and ZnCo₂O₄ oxide, uniformly distributed on Bi₂S₃ rods. Bi₂S₃@ZC-cLDHs heterostructures exhibited superior photocatalytic efficiency for levofloxacin (LF) degradation compared to Bi₂S₃ and ZC-cLDHs under same catalytic conditions. The enhanced photodegradation efficiency results from the increased surface area and the establishment of a heterojunction at the interface of Bi₂S₃ rods and ZC-cLDHs. In addition, the photocatalytic degradation efficiency of LF enhanced from 74.8% to 90.1% with the addition of persulfate (PS) as an activating under visible light, utilizing a catalyst loading of Bi₂S₃@ZC-cLDHs at 1.0 g L^-1, initial concentration of 20 ppm, PS loading of 0.25 g L^-1, and light exposure duration of 90 minutes. The Z-scheme established the photocatalytic mechanism for the degradation of LF using Bi₂S₃@ZC-cLDHs with PS activation. Radical trapping tests demonstrated that O₂˙^- and h⁺ were the significant active species. The combination of PS and catalyst had a synergistic effect, wherein S₂O₈ ^2- interacted with electrons to create SO₄˙^- during the photocatalytic process. The analysis using LC-MS provided a thorough understanding of possible photocatalytic breakdown path of LF; the photoproducts were small-sized molecules with little impact on the environment.