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The widely used nanosized zero-valent iron (nZVI or nFe 0 ) particles and their composite material lose reductive nature during application, and the stability of transformed composite material for repeatable application is not addressed to date. To shed light on this, nZVI was synthesized from scrap material and immobilized on functionalized biochar (fBC) to prepare nZVI-fBC composite. Comparative study between nZVI and nZVI-fBC composite on the removal of chlorinated antibiotic chloramphenicol from different water types was conducted. The results suggested that nZVI was solely responsible for reduction of chloramphenicol. Whereas nZVI-fBC could be applied once, within a few hours, for the reduction of chloramphenico (29–32.5%) and subsequently sorption (67.5–70.5%) by transforming to a fully magnetic composite (nFe 3 O 4 -fBC) gaining stability with synergistic sorption performance. In both cases, two reduction by-products were identified namely 2-chloro-N-[1,3-dihydroxy-1-(4-aminophenyl)propan-2-yl]acetamide ( m / z 257) and dechlorinated N-[1,3-dihydroxy-1-(4-aminophenyl)propan-2-yl]acetamide ( m / z 223). The complete removal of 3.1 µM L −1 of chloramphenicol in different water was faster by nZVI-fBC (∼12–15 h) than by stable nFe 3 O 4 -fBC composite (∼18 h). Both nZVI-fBC and nFe 3 O 4 -fBC composites removed chloramphenicol in the order: deionized water > lake water > synthetic wastewater. nFe 3 O 4 -fBC showed excellent reusability after regeneration, with the regenerated nFe 3 O 4 -fBC composite (after 6 cycles of application) showing significant performance for methylene blue removal (∼287 mg g −1 ). Therefore, the transformed nFe 3 O 4 -fBC composite is a promising and reusable sorbent for the efficient removal of organic contaminants. [ABSTRACT FROM AUTHOR]