Effective photodegradation of tetracycline by narrow-energy band gap photocatalysts La2-xSrxNiMnO6 (x = 0, 0.05, 0.10, and 0.125).

Owing to the adverse effects of tetracycline (TC) on human health, it should be completely degraded by the active species that are usually generated by photocatalysts under ultraviolet (UV) radiation. Such radiation which accounts for about only 5% energy of the sunlight. In general, obtaining the active species of the photocatalysts upon irradiation with light is challenging because of the wide spectrum of light. To address this, novel photocatalysts, La 2-x Sr x NiMnO 6 (x = 0, 0.05, 0.10, and 0.125, denoted by LNMO, LSNMO005, LSNMO010, and LSNMO0125, respectively), with high-potential valence band edge (E VB), abundant oxygen vacancies (O V -s), and narrow-energy band gap (E g) were designed and prepared via a solid-state reaction. The synthesized powders were characterized by several techniques. Sr2+ doping was found to significantly raise the E VB of LNMO and slightly increase its O V -s. The highest E VB , maximum O V -s, longest lifetime, and fastest transferring speed of the photogenerated carriers were observed for LSNMO010. It was found that LSNMO010 could effectively photodegrade TC in 240 min. TC could also undergo thermocatalytic degradation at 100 °C in 90 min in the presence of LSNMO010. However, TC could not be effectively degraded either by photolysis or thermolysis alone, in the absence of LSNMO010. It was concluded that the photogenerated holes (h +-s) and hydroxyl radicals (•OH) played dominant roles in the photodegradation of TC. Measurement of the total organic carbon (TOC) revealed that only 18.28% TOC was removed by direct photolysis, and about 83.90% TOC was mineralised by LSNMO010. The outcomes of this work suggest that introduction of dopants to increase O V and to obtain high-potential E VB in double perovskites could be a novel methodology for designing a class of narrow- E g photocatalysts that can effectively degrade TC. Image 1 • Sr-doping reduces energy band gap leading to more widened light respond range. • Sr-doping lifts valance band edge to higher potential value. • XPS analysis shows Sr-doping photocatalysts possess more oxygen vacancies. • Sr-doped photocatalyst show better catalytic ability than Sr-free photocatalyst. • Sr-doped photocatalyst also has potential to apply in degrading TC using waste heat. [ABSTRACT FROM AUTHOR]