Fig. 4. Emission quenching of carbon nanofibers in aqueous suspension in the presence of metal ions at (A) 3.3 mM and (B) 50.0 μM concentration. (C) and (D) The normalised emission of carbon fibers in the presence of Fe(ii) and Fe(iii) respectively as a function of concentration from 6.25 μM to 5.0 mM. Inset shows in greater detail the low concentration region from 6.25 μM to 50.0 μM. All emission was taken at 350 nm excitation.