Complexity in the Photofunctionalization of Single-Wall Carbon Nanotubes with Hypochlorite

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The reaction of aqueous suspensions of single-wall carbon nanotubes (SWCNTs) with UV-excited sodium hypochlorite has previously been reported to be an efficient route for doping nanotubes with oxygen atoms. We have investigated how this reaction system is affected by pH level, dissolved O₂ content, and radical scavengers and traps. Products were characterized with near-IR fluorescence, Raman, and XPS spectroscopy. The reaction is greatly accelerated by removal of dissolved O₂ and strongly suppressed by TEMPO, a radical trap. Alcohols added as radical scavengers alter the reaction efficiency and the product peak emission wavelengths. Photofunctionalization with 300 nm irradiation is substantially less efficient at pH levels low enough to protonate the OCl^– ion to HOCl. We deduce that in mildly treated high pH samples, the main product is sp² hybridized O-doped adducts formed by reaction of SWCNTs with atomic oxygen in its ³P (ground) level. By contrast, treatment under low pH conditions leads to sp³ hybridized SWCNT adducts formed by the addition of secondary radicals from reactions of ^•OH and ^•Cl. There is also evidence for additional photoreactions of product species under stronger irradiation. Researchers using photoexcited hypochlorite for SWCNT functionalization should be alert to the range of products and the sensitivity to reaction conditions in this system.