Need a balance? relationship between removal reactivity of cationic dye and bacterial cytotoxicity by iron carbide-stabilized nano zero-valent iron.

• Relationship of reactivity and cytotoxicity needs to be clarified for nZVI materials. • Encapsulation of nZVI/Fe 3 C heterojunction in PGC skeleton enhances the air stability. • nZVI/Fe 3 C/PGC-700 exhibits a RhB removal efficiency of 89.2 % within 10 min at pH = 3. • Fe 3 C-bonded nZVI with a stable reactivity has high biocompatibility and low toxicity. • It reveals how the Fe 3 C-bonded nZVI can enhance its stability and lower its toxicity. Nano zero-valent iron (nZVI) as an active species for environmental applications usually suffers from its poor stability by corrosion and strong toxicity to microbes. To relieve the fast surface passivation and cytotoxicity (for Escherichia coli, E. coli), in-situ modification of nZVI with iron species may be a feasible strategy for strengthening the stability/reactivity and biocompatibility of nZVI-based materials. Here, nZVI/iron carbide heterojunctions are in situ embedded in partly-graphitized carbon (nZVI/Fe 3 C/PGC) using a one-step carbothermal synthesis method. nZVI/Fe 3 C/PGC-700 (700 °C) with a specific surface area of 126.04 m2/g exhibits a promising Rhodamine B (15 mg/L) removal efficiency of 89.2 % within 10 min at pH = 3. After 15 d storage in air or the 4th use, the crystalline structure and morphology of nZVI/Fe 3 C/PGC-700 remain basically unchanged. Due to the in-situ binding of nZVI and Fe 3 C with mixed valence, the surface oxidation is quite difficult to occur, thereby stabilizing the reducing capacity of nZVI. The encapsulation of nZVI/Fe 3 C heterojunctions in PGC structure also contributes to the structural stability. Although nZVI/Fe 3 C/PGC-700 can influence the metabolic functions of E. coli cells and the integrity of cell structure, this Fe 3 C-bonded nZVI exhibits a lower bacterial cytotoxicity than bare nZVI and nZVI@SiO 2 as indicated by lactate dehydrogenase and reduced superoxide dismutase assays. This novel strategy provides an interesting option for design of carbides-stabilized nZVI with balanced reactivity and cytotoxicity. [ABSTRACT FROM AUTHOR]