Multi-walled carbon nanotubes (MWCNTs) were synthesized by chemical vapor deposition (CVD) using ferrocene as the carbon and iron-catalyst precursor and were evaluated for antibacterial activity against Escherichia coli ATCC 25,922. The as-grown material was characterized by X-ray diffraction (XRD), Raman spectroscopy, field-emission scanning electron microscopy (FE-SEM), and energy-dispersive X-ray spectroscopy (EDX). The characterization results confirmed the formation of graphitized multi-walled nanotube structures and the presence of iron-containing residues derived from the ferrocene precursor. Antibacterial activity was assessed by agar well diffusion, broth microdilution, and viable-count plating. A concentration-dependent reduction in bacterial growth was observed over the tested range of 1–512 µg/mL. The minimum inhibitory concentration (MIC) was determined to be 256 µg/mL based on the absence of visible bacterial growth, with blank-corrected quantitative measurements providing supplementary confirmation of the inhibitory endpoint. Viable-count analysis on drug-free Mueller–Hinton agar showed no recoverable colonies at 256 and 512 µg/mL, supporting a minimum bactericidal concentration (MBC) of 256 µg/mL under the experimental conditions. In the agar well-diffusion assay, inhibition-zone diameters were 26, 21, 19, 9, and 7 mm at 512, 256, 128, 64, and 32 µg/mL, respectively, whereas no inhibition was observed in the negative control. These findings demonstrate concentration-dependent antibacterial activity of the as-grown ferrocene-derived MWCNT preparation against E. coli ATCC 25,922. Because the material was evaluated without post-synthesis purification, the observed activity represents the response to the as-grown preparation, including potential contributions from synthesis-derived components.
