Experimentally Determined Redox Potentials of Individual (n,m) Single‐Walled Carbon Nanotubes

Abstract

Ever since the discovery of carbon nanotubes (CNTs), many groups have endeavored to understand the fundamental properties of the CNTs. The redox properties (i.e. electronic densities, the Fermi levels, redox potentials) of single-walled carbon nanotubes (SWNTs) are related to the structures of SWNTs that have a specified diameter and chirality angle uniquely related to a pair of integers (n,m); the so-called chiral indices. [1,2] Many attempts have been made to determine the electronic properties of SWNTs using scanning tunneling spectroscopy, [3] redox titrimetry, [4] photoluminescence (PL) measurements, [5][6][7] and spectroelectrochemistry; [8][9][10][11][12][13] however, the success in the determination of the redox properties as already reported has been low. Recently, Paolucci et al. [12] employed Vis-near-IR absorption spectroelectrochemistry to estimate the redox potentials of the SWNTs dissolved in an ultradry dimethylsulfoxide (DMSO) solution; however, it is not easy to determine the redox potentials of isolated (n,m)SWNTs using this method because SWNTs with several different chiral indices have band gaps in the near-IR region that overlap one another. We now describe a simple method for the determination of the redox potentials of many (in this study, fifteen) individual (n,m)SWNTs using near-IR PL spectroelectrochemistry in an aqueous medium.Strategic approaches toward the solubilization of CNTs are essential for many applications of CNTs [14] and numerous dispersants including carboxymethylcellulose sodium salt (CMC, Figure S1a in the Supporting Information) [15] have been used to individually dissolve SWNTs. In this study, we fabricated a non-fluorescent transparent indium tin oxide (ITO) electrode modified with a cast film of CMC/poly-(diallyldimethylammonium chloride) (PDDA; Figure S1b in the Supporting Information) that contained isolated SWNTs (for details, see Experimental Section in the Supporting Information).We have discovered that we can determine the redox potentials of isolated SWNTs having their own chirality indices by in situ near-IR PL spectroelectrochemistry at the fabricated modified ITO electrode. This modified film retains the isolated SWNTs and the spectroelectrochemical results are analyzed with the Nernst equation.Externally applied potentials were changed in the range of ) and oxidized form (SWNT n+ ) when the external potential was applied to the electrode in arbitrary steps from 0.0 V to À1.0 V and from 0.0 V to + 1.1 V, respectively. After each potential step, the applied potential was returned to 0.0 V and it was confirmed that no significant spectral change in the SWNT had occurred, namely, the SWNTs in the film are stable during these electrochemically driven redox processes. This behavior of the SWNTs is consistent with those in Visnear-IR absorption [8b] and Raman [10b] spectroelectrochemical studies.We carried out in situ near-IR absorption spectroelectrochemistry using the modified electrode. The near-IR absorption spectra of the individually solubilized SWNTs wer...

Semiconducting single-walled carbon nanotubes sorting with a removable solubilizer based on dynamic supramolecular coordination chemistry

“…As shown in Fig. 4h, sem-SWNTs with (n,m) ¼ (6,5), (7,5), (7,6), (8,3), (8,4), (8,6), (8,7), (9,4), (9,5), (9,7), (10,2), (10,3), (10,5), (10,6), (11,3), (11,4), (11,6) and (12,2) were found to exist in the solution. In order to evaluate the extraction efficiency for each (n,m) chirality of the tubes, we calculated the relative contents of each SWNT based on the calibrated PL intensity using the method reported by Oyama et al 57 The calibrated contents of the SWNT species deduced from the PL mapping are shown in Supplementary Table 1, in which SWNTs with (n,m) ¼ (7,6), (8,6), (9,4) and (10,2) were enriched for the sample using CP-Zn.…”

“…Not only their structural characteristics, but also opto-electronic properties derived from their diameters and chiral indices, denoted as (n,m)SWNTs, are important for a deep understanding of their fundamental intrinsic properties [1][2][3][4][5][6][7][8][9][10] . Highly purified semiconducting SWNTs (sem-SWNTs) not containing metallic SWNTs (met-SWNTs) are specifically required for electronic devices, such as field-effect transistors [11][12][13][14] and photovoltaic applications 15,16 because the met-SWNTs decrease and reduce the efficiency of their associated devices 17,18 .…”

<i>In Situ </i>Photoluminescence Spectroelectrochemistry for Determination of Electronic States of Single-Walled Carbon Nanotubes

“…The PL signals from the SWNTs are originated from the exciton (recombination of electronhole pairs at the band gaps) of the isolated SWNTs, which is well-known in the carbon nanotube science. We fabricated a transparent indium tin oxide (ITO) electrode modified with a film of carboxymethylcellulose sodium salt (CMC)/poly(diallyldimethylammonium chloride) [30]. From the near-IR PL spectrum of the film (Fig.…”

“…Based on the results of the PL imaging and single SWNT PL spectroscopy, the stepwise quenching behavior of the PL from a single (7,5)-SWNT was detected as the outer-applied potentials increased. The Nernst equation analysis of the obtained potential-dependent PL plots provided the oxidation and reduction potentials of the (7,5) tube as 0.41 V and -0.38 V vs. Ag/AgCl, respectively, which shift from those of the bulk (7,5)-SWNTs (oxidation: 0.54 V and reduction: -0.47 V [30]). We further observed a PL blueshift [61][62][63][64] and narrowing of the line width as the external-applied potential to the single SWNT increases.…”

Probing the charging mechanisms of carbon nanomaterial polyelectrolytes

“…is critical: for example, too many functional addends can cause the loss of (opto)electronic and mechanical properties, too few and there may be no benefit to nanocarbon solubility or compatibility with a polymer matrix. 21 The first nanotube redox potentials have been probed using spectroelectrochemical methods, [22][23][24] and the redox potentials of reactants in aqueous systems are well studied. However, the exact potential of charged nanocarbon polyelectrolytes and redox potentials of reactants in anhydrous, aprotic solvents are not well known.…”