Biotransformation of 2D Nanomaterials through Stimulated Bacterial Respiration-Produced Extracellular Reactive Oxygen Species: A Common but Overlooked Process.

The biotransformation of 2D nanomaterials is still poorly understood, although their environmental fates are becoming an increasing concern with their broad applications. Here, we found that Ti 3 C 2 T x nanosheets, a typical 2D nanomaterial, could be oxidized by reactive oxygen species (ROS) produced by both Gram-negative ( Escherichia coli and Shewanella oneidensis ) and Gram-positive ( Bacillus subtilis ) bacteria, with the formation of titanium dioxide (TiO 2 ) on the nanosheet surfaces and impairment of structural integrity. Specifically, Ti 3 C 2 T x nanosheets stimulated bacterial respiration Complex I, leading to increased generation of extracellular O 2 •- and the formation of H 2 O 2 and • OH via Fenton-like reactions, which intensified the oxidation of the nanosheets. Surface modifications with KOH and hydrazine (HMH), especially HMH, could limit bacterial oxidation of the nanosheets. These findings reveal a common but overlooked process in which oxygen-respiring bacteria are capable of oxidizing 2D nanosheets, providing new knowledge for environmental fate evaluation and future design of functional 2D nanomaterials.