Charging Nanowalls: Adjusting the Carbon Nanotube Isoelectric Point via Surface Functionalization

Abstract

Controlling the point of zero charge (PZC) of carbon nanotubes is important for depositing finely dispersed metal nanoparticles from precursors in solution for fabricating chemical and biological sensor and catalyst surfaces. HiPco single-walled carbon nanotubes (p-SWNTs) were functionalized with carboxylic acid (COOH-SWNT), nitroso (NO-SWNT), and maleic anhydride (MA-SWNT) groups. The presence of attached moieties on the carbon nanotube surface was verified using X-ray photoelectron (XPS) and attenuated total reflection infrared (ATR-IR) spectroscopies. PZC measurements (in parentheses) were in the descending order: NOSWNTs (7.5) > p-SWNTs (3.5) > MA-SWNTs (2.0) > COOH-SWNTs (1.2). The trend in measured PZC values correlated with the electron withdrawing character of the attached moieties, consistent with Hammett σ constants. Variations in the electron withdrawing character of the moieties led to SWNTs with differing semiconducting character, as observed in the UV-vis-NIR E 11 semiconducting region and Raman D-to-G band ratios. These results suggest a tunability of the SWNT PZC via sidewall functionalization, a factor to consider for practical SWNT nanomaterial fabrication.

Characterizing Functionalized Carbon Nanotubes for Improved Fabrication in Aqueous Solution Environments

“…4) as observed. In our final case study, variations in the measured PZC were seen between differently functionalized SWNT structures (McPhail et al, 2009). Fig.…”

“…Further analysis by ATR-IR and Raman spectroscopies were performed as described by Hull et al (2006). The experimental procedure for the third case study (McPhail et al, 2009) was as follows: (1) COOH-SWNTs were prepared by refluxing in H 2 SO 4 /HNO 3 according to Lu et al (2007). A 30.0 mL solution of 3:1 concentrated nitric-to-sulfuric acid ratio was added to a 100-mL round-bottom glass flask along with 60.1 mg of p-SWNTs.…”

“…Variations in the electron releasing/withdrawing character of the substituents correlate well with the observed PZC trend. In our previous work (McPhail et al, 2009), we postulated that the PZC was dependent on SWNT electronic structure.…”

Closing the gap: accelerating the translational process in nanomedicine by proposing standardized characterization techniques

“…13 TGA is limited by the degradation characteristics of the nanomaterial; easily degradable materials, such as biodegradable polymers, will be more difficult to quantify using TGA than inorganic nanomaterials because they contain common TGA leaving groups such as carboxyls. Hybrid electron microscopy techniques, such as scanning electron microscopy (SEM)-Raman and energy-filtered TEM, discussed in the following section, may be employed to overcome some of the limitations of TGA and yield three-dimensional spatial details with sufficient sample processing time.…”

“…FT-IR can also be used as a titration technique to detect relative amounts of different functionalities, but generally is not a quantitative tool. 13,21 Attenuated total reflectance is a direct sample analysis technique that has been used for FT-IR analysis, and is particularly helpful for analyzing the chemical fingerprint of a nanomaterial without excessive sample preparation. Samples that are sensitive to the solvents or pressure required to prepare a typical FT-IR sample have been analyzed with this technique because FT-IR spectra can be obtained from pure bulk materials on the attenuated total reflectance probe.…”