Covalent Functionalization of Carbon Nanomaterials with Iodonium Salts

Abstract

Covalent functionalization significantly enhances the utility of carbon nanomaterials for many applications. Herein we report an efficient method for the covalent functionalization of carbon nanotubes and graphite. This reaction involves the reduction of carbon nanomaterials with sodium naphthalide followed by the addition of diaryliodonium salts. Carbon nanotubes, including singlewalled, double-walled, and multi-walled variants (SWCNTs, DWCNTs, MWCNTs), as well as graphite, can be efficiently functionalized with substituted arene and heteroarene iodonium salts. The preferential transfer of phenyl groups containing electron-withdrawing groups was demonstrated by reactions with unsymmetrical iodonium salts. The lower reactivity of iodonium salts relative to the more commonly used diazonium ions, presents opportunities for greater diversity in the selective functionalization of carbon nanomaterials.

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“…[34] We have applied a recently developed Scheme for iodonium functionalization to precisely attach single aromatic rings to the sidewalls of SWCNTs. [35] This method allows us to confidently install a pyridyl group attached in the 4 position to the SWCNT for anchoring of the 5,10,15,20-tetraphenyl-porphyrin iron(III) perchlorate (Fe(tpp)ClO 4 ) that serves as our redox active CO binding site.In developing an optimal sensor, the density of the CO binding and transducing sites is critical. We controlled the density of pyridyl groups on the SWCNTs by the ratio of pristine SWCNTs to sodium naphthalide and pyridyl iodonium salt during synthesis, (see Figure S2 in the Supporting Information).…”

“…We controlled the density of pyridyl groups on the SWCNTs by the ratio of pristine SWCNTs to sodium naphthalide and pyridyl iodonium salt during synthesis, (see Figure S2 in the Supporting Information). Using a ratio of 1:0.05:0.05 equivalents of pristine CNT, sodium naphthalide and iodonium salt, respectively, [35] we obtained 1.4 pyridyl groups per …”

“…[34] We have applied ar ecently developed scheme for iodonium functionalization to precisely attach single aromatic rings to the sidewalls of SWCNTs. [35] This method allows us to confidently install ap yridyl group attached in the 4p osition to the SWCNT for anchoring of the 5,10,15,20-tetraphenyl-porphyrin iron(III) perchlorate (Fe(tpp)ClO 4 )t hat serves as our redox active CO binding site.…”

“…We controlled the density of pyridyl groups on the SWCNTs by the ratio of pristine SWCNTs to sodium naphthalide and pyridyl iodonium salt during synthesis ( Figure S2 in the Supporting Information). Using ar atio of 1:0.05:0.05 equivalents of pristine SWCNTs,s odium naphthalide,a nd iodonium salt, respectively, [35] we obtained 1.4 pyridyl groups per 100 SWCNT carbon atoms (F-SWCNT-1). 1 HNMR analysis of the post-functionalization filtrate confirmed that the pyridyl groups were the dominant functional group on the SWCNTs ( Figure S4).…”

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“…In addition to the swelling of the random nanowire network, SWCNTs also display conductance changes induced by charge transfer or dipolar pinning/scattering caused by the analyte.P inning and charge transfer result in ar eduction of the mobile charge carriers,and this feature can be detected by changes in the threshold gate voltages in field-effect transistor (FET) devices. [27] Functionalization of SWCNTs to impart selectivity is key;h owever, the chemistry is complicated by the fact that core characterization methods like solution NMR spectroscopy and crystal structure determination are not possible with these nanomaterials.H owever,t he field continues to evolve with the refinement of methods for the attachment of functional groups with greater precision [28] and that can undergo subsequent functionalization [29] to add recognition elements. [30] Theu se of nanowires for chemical sensing has recently been reviewed.…”