Heterogeneous degradation of carbamazepine by Prussian blue analogues in the interlayers of layered double hydroxides: performance, mechanism and toxicity evaluation

Prussian blue analogues (PBA) are efficient catalysts for peroxymonosulfate (PMS) activation. However, the longevity and recovery ability of PBA are very poor, which limits their practical applications. In this study, for the first time, we successfully incorporated a nanosheet-like PBA into the interlayers of layered double hydroxides (LDH) (PBA-LDH). The morphology and physicochemical characteristics of the as-synthesized PBA-LDH were well characterized using SEM, TEM, XRD, FTIR and XPS. PMS activation via PBA-LDH toward carbamazepine (CBZ) degradation was systematically examined. The activation of PMS via PBA alone could only achieve a maximum of 31.8% degradation efficiency for CBZ within 15min. However, complete degradation of CBZ was achieved via a PBA-LDH-activated PMS system within a wide pH range of 3.0 to 9.0. ESR measurements and radical scavenging experimental results revealed that SO4- is the most active species in CBZ degradation. XPS analysis confirmed a reversible valence equilibrium between the metal ions and the recovery of surface-adsorbed oxygen, ensuring stable catalytic activity. Notably, the CBZ degradation in the PBA-LDH activated system remained as high as 95.7% after six consecutive runs. Meanwhile, only 8.1 g L-1 cobalt ion and 5.4 g L-1 iron ion were leached from PBA-LDH after the degradation reaction; thus, it is non-toxic to aqueous environments. In addition, a possible pathway for CBZ degradation was proposed, and an eco-toxicity assessment of the oxidation intermediates was also performed.