Nanowall Potentials: Effects of Covalent Functionalization on the Carbon Nanotube Point of Zero Charge

A working knowledge of the carbon nanotube isoelectric points is important for solution phase synthesis of precursors of nanoparticle surfaces for biosensor and catalyst applications. The effect of attaching moieties of various electron-withdrawing character was studied by functionalizing single-walled carbon nanotubes with carboxylic acid, maleic anhydride, and nitroso groups. Covalent functionalization was confirmed by Xray photoelectron and attenuated total reflection infrared spectroscopies, and thermogravimetric analysis. Point of zero charge (PZC) measurements indicated that functionalization varied the PZC by as much as 6.3 pH units. UV-vis-NIR absorption in the E11 region and Raman D to G band ratios revealed changes in the semiconducting character of functionalized nanotubes, accompanying changes in the PZC. The results indicate that nanowall functionalization can play a major role in tuning the carbon nanotube isoelectric point, enabling fabrication of a variety of supports