Using Nonionic Surfactants for Production of Semiconductor-type Carbon Nanotubes by Gel-based Affinity Chromatography

Single-wall carbon nanotubes (SWCNTs) have remarkable properties based on their electronic properties, i.e., metallic or semiconducting types, but as-grown SWCNTs contain a mixture of both types. Presented here is an improved and detailed method for producing highly enriched semiconducting SWCNTs from a colloidal suspension of as-grown SWCNTs through agarose gel column-based affinity chromatography. After a 2 wt% sodium dodecyl sulphate (SDS) aqueous dispersion of SWCNTs is passed through the gel column, metal-type SWCNTs preferentially elute out using a 1.5 wt% SDS solution. Semiconductor-type SWCNTs are subsequently recovered from the column using a 2 wt% Pluronic F77 surfactant solution eluent. The semiconductor-enriched fraction purity is in the 90-95% range, based on detailed UV-vis-NIR absorption and resonant Raman spectroscopy characterization of the particulate suspension. Semiconductor-type SWCNTs are recovered in solid form by evaporating the suspension fluid, and heating the dried sample in air to a temperature just above the Pluronic decomposition temperature. Using Pluronic and other nonionic-type surfactants can aid the scalability of the chromatographic production of semiconducting SWCNT samples

Photoluminescence Dynamics of Aryl sp³ Defect States in Single-Walled Carbon Nanotubes

Photoluminescent defect states introduced by sp³ functionalization of semiconducting carbon nanotubes are rapidly emerging as important routes for boosting emission quantum yields and introducing new functionality. Knowledge of the relaxation dynamics of these states is required for understanding how functionalizing agents (molecular dopants) may be designed to access specific behaviors. We measure photoluminescence (PL) decay dynamics of sp³ defect states introduced by aryl functionalization of the carbon nanotube surface. Results are given for five different nanotube chiralities, each doped with a range of aryl functionality. We find that the PL decays of these sp³ defect states are biexponential, with both components relaxing on time scales of ∼100 ps. Exciton trapping at defects is found to increases PL lifetimes by a factor of 5–10, in comparison to those for the free exciton. A significant chirality dependence is observed in the decay times, ranging from 77 ps for (7,5) nanotubes to >600 ps for (5,4) structures. The strong correlation of time constants with emission energy indicates relaxation occurs <i>via</i> multiphonon decay processes, with close agreement to theoretical expectations. Variation of the aryl dopant further modulates decay times by 10–15%. The aryl defects also affect PL lifetimes of the free <i>E</i>₁₁ exciton. Shortening of the <i>E</i>₁₁ bright state lifetime as defect density increases provides further confirmation that defects act as exciton traps. A similar shortening of the <i>E</i>₁₁ dark exciton lifetime is found as defect density increases, providing strong experimental evidence that dark excitons are also trapped at such defect sites