Integrated influence of bulk cations on the degradation of florfenicol by smectite-intercalated ultrafine zero-valent iron

Smectite intercalated ultrafine iron clusters (SUZVI) demonstrate exceptional reactivity against contaminants attributed to the nanoscale interlayer confinement which restricts the iron clusters to dimensions of about 0.5 nm. Cations confined in the smectite interlayer region would manifest complex impact on the configuration and composition of this region and hence the proceeding of the degradation reaction. This study aims to clarify the mechanisms by which bulk K⁺, Mg²⁺, and Ca²⁺ influence the configuration of SUZVI and its reactivity toward florfenicol (FF) as a model contaminant. Our findings revealed that each cation distinctly influenced the inter-particle aggregation, and the interlayer spacing, water content, and Brønsted acidity of SUZVI, thereby affecting its degradation efficiency to varying degrees. Divalent cations such as Mg²⁺ and Ca²⁺ induced a reaction favorable interlayer but also led to pronounced inter-particle aggregation, which generally diminished degradation efficiency. An exception was observed at 2 mM of Mg²⁺, which uniquely promoted an enhanced dechlorination efficiency. K⁺ exhibited a contrasting effect on the interlayer region yet protected SUZVI from water corrosion, manifesting a 1.7 times higher electron utilization efficiency than SUZVI in presence of Mg²⁺. These insights offer mechanistic understanding into tailoring the reactivity of SUZVI for optimizing the efficiency of its practical applications.