Fluorescence Quenching of Single-Walled Carbon Nanotubes in SDBS Surfactant Suspension by Metal Ions : Quenching Efficiency as a Function of Metal and Nanotube Identity

The effects of both the metal ion and the counterion on the fluorescence of SDBS-surfacted single-walled carbon nanotubes (SWNTs) have been investigated for solutions of group 2, 12, and 13 metal salts with a [Mn+] of between 0.5 and 5 mM per 15 mg.L-1 of SWNT. The following metal salts cause a decrease in fluorescence of the SWNTs:  MgCl2, Mg(SO4), Mg(OAc)2, CaCl2, Ca(OAc)2, SrCl2, BaCl2, Ba(OAc)2, Zn(SO4), CdCl2, Cd(SO4), Cd(OAc)2, HgCl2, and Hg(OAc)2. In contrast, Ga2(SO4)3, and Al(NO3)3 show no reduction in fluorescence over the concentration range studied. The decrease in fluorescence is found to be due to quenching rather than bundling, acid suppression, or spectral bleaching. The Stern−Volmer quenching constants are found to depend on the identity of the metal ion, the anion, and the diameter (related to the n,m value) of the SWNT. For group 2 metals, the quenching efficiency follows the trend of increasing ionic radii (Mg < Ca < Sr < Ba), whereas the relationship between the group 12 metals is mor...