Performance and influencing mechanisms of magnetically separable Ni-M layered double hydroxides (M = Fe, Al) for catalytic ozonation

[Display omitted] •Magnetically separable Ni-M LDHs (M = Fe, Al) were prepared for catalytic ozonation.•Ni-M LDHs catalyzed ozonation process achieved highly efficient RhB degradation.•Ni-M LDHs presented different structure features but similar catalytic performances.•Formed OH, O2−, and 1O2 mainly contributed to RhB degradation during the process.•Difference in catalytic ozonation mechanisms over Ni3-Fe and Ni2-Al LDHs were revealed. From a preliminary performance comparison of several layered double hydroxides (LDHs), magnetically separable Ni-M LDHs (M = Fe, Al) were synthesized and applied as efficient ozonation catalysts for degrading dye Rhodamine B (RhB). As proved by various characterizations, the micromorphology, nanostructure size, and porous feature of the synthesized Ni-M LDHs significantly varied with different metal components. Among them, Ni3-Fe LDH and Ni2-Al LDH possessed a relatively larger specific surface area to react with O3 interfacially, thereby exhibiting excellent catalytic ozonation performance. The RhB was almost completely degraded within 60 min, and the removal efficiencies of COD and TOC reached above 70% and 50%, respectively. The effects of catalyst dosage, initial dye concentration, solution pH, and coexisting inorganic anions on RhB degradation were studied systematically. ESR measurements and radical quenching experiments indicated that OH, O2−, and 1O2 are primary reactive oxygen species (ROS), while 1O2 induced the most dominant degradation contribution. According to the variations of ROS formation and material properties during the catalytic ozonation process, the possible reaction mechanisms were proposed. Moreover, the differences involved in the redox of multivalent metals and the transformation of surface hydroxyls over Ni-Fe and Ni-Al LDHs were further revealed.