Efficient micropollutants degradation by ferrate(VI)-Ti/Zn LDH composite under visible light: Activation of ferrate(VI) and self-formation of Fe(III)-LDH heterojunction

This paper presents Fe(VI) combined with Ti/Zn layered double hydroxide (Fe(VI)-Ti/Zn LDH) as a composite to degrade organic pollutants (pesticides and pharmaceuticals) under visible light (VL). The Fe(VI)-LDH/VL system was shown to effectively activate Fe(VI) and simultaneously enhance separation and migration of electrons-holes on the Ti/Zn LDH surface. Furthermore, the Fe(III) particles resulting from the Fe(VI) reduction were adsorbed and coordinated onto the LDH surface to form an in-situ heterojunction photocatalyst which narrowed the wide bandgap from 3.08 eV to 1.44 eV of the LDH and achieved further oxidation of pollutants. Detailed kinetic and mechanistic investigations using the pesticide, imidacloprid (IMI), revealed multi-oxidant intermediate species (FeV/FeIV, OH, hVB+ and O2−) involved in degrading the parent micropollutant and yielding oxidized products. This study also assessed the application of Fe(VI)-Ti/Zn LDH composite to other pesticides and pharmaceuticals (carbaryl (CAB) and metribuzin (MBZ), trimethoprim (TMP) and carbamazepine (CBZ)), and exhibited satisfactory micropollutants removal. The newly reported VL-induced Fe(VI) activation system, based on Fe(VI)-Ti/Zn LDH composite, may be an effective multi-oxidant strategy to oxidize pollutants in water.