Peroxymonosulfate activation by Ni-Co nanoparticles encapsulated in nitrogen-doped carbon derived from Co-doped Ni metal-organic frameworks for efficient enrofloxacin degradation

Nitrogen-doped carbon (NC) material encapsulating bimetallic nanoparticles has emerged as promising catalyst for the activation of peroxymonosulfate (PMS) in water treatment. This study presents the synthesis of Ni-Co nanoparticles anchored on porous NC via metal-nitrogen bonds, utilizing Co recovered from spent lithium-ion batteries. The resulting magnetic catalysts, denoted as Ni(Co)@NC-x, were derived from Co-doped Ni metal- -organic frameworks and were employed for PMS activation to degrade enrofloxacin (ENR). Catalyst optimization revealed that a carbonization temperature of 500 degrees C and a balanced doping ratio are crucial for achieving optimum performance. Furthermore, the addition of Co was found to enhance the graphitization degree, stability, and magnetism of the catalyst, while also reducing the particle size of the metal nanoparticles, leading to a more uniform dispersion. Ni(Co)@NC (Ni(Co)@NC-3) performed the best, degrading 98 % of ENR within 12 min and improving the degradation kinetics by 4.81. Active species identification and density functional theory calculations confirmed that Ni(Co)@NC primarily activates PMS through a sulfate radical mediated radical route, contributing to the efficient ENR degradation. The electron transfer processes play a significant role in ENR removal, confirming the importance of the rapid redox cycling of metal and the metal-support interactions in PMS activation. The study proposes a plausible reaction mechanism and potential ENR degradation pathway, which were further supported by the reduced toxicity of transformation residues as confirmed by the Toxicity Estimation Software Tool. The sustained performance of Ni(Co)@NC upon continuous PMS activation suggests its potential as a reliable PMS activator. This work provides a theoretical and experimental foundation for the development and application of M1(M2)@NC catalysts with excellent environmental adaptability and stability.