Purification and Functionalization of MWCNT

The purification and functionalization of the MWCNT were accomplished as previously described. ^{36 –38} This activity was carried out in a Microwave Accelerated Reaction System CEM Mars (Matthews, NC, USA) fitted with internal temperature and pressure controls. The 100 mL reaction chamber was lined with Teflon PFA^® with an operating range of 0~200 °C and 0~200 psi. The residual metals were removed via microwave induced reaction with 1N HNO₃ followed by a reaction with saturated ethylenediamine tetra-acetate in CH₃COOH. ^{39 (link)} The purified MWCNT (PD-MWCNT) were added to the reaction chamber together with 40 mL of a mixture of 1:1 70 % nitric acid and 97 % sulfuric acid. With the microwave power set to 95 % of the maximal possible 1600 watt output, the reaction was carried out for 20 min at a temperature of 140 °C. The suspension was filtered through a 10 μm PTFE membrane, washed with deionized water (DI H₂O) to a neutral pH and vacuum dried at 70 °C. This sample derivative was designated COOH-MWCNT. A variety of different analytical techniques were used to characterize the MWCNT, including Energy Dispersive X-ray Spectroscopy (EDS, Oxford Instrument, Oxfordshire, UK) to identify the elemental composition of the MWCNT. The Fourier Transform Infrared spectroscopy (FTIR) measurements were carried out in purified KBr pellets using a PerkinElmer Spectrum One instrument (Downers Grove, IL, USA). Thermogravimetric analyses (TGA) were performed using a Pyris 1 TGA (Perkin-Elmer Inc., Covina, CA, USA) from 30 °C to 900 °C under a flow of air at 10 mL/min and a heating rate of 10°C per min. Scanning Electron Microscopy (SEM) using a LEO 1530 VP SEM equipped with an energy-dispersive X-ray analyzer was used to study the morphology of the samples. Zeta-potential measurements of the MWCNT suspensions were performed using a ZetaSizer Nano-ZS Instrument (Malvern Instruments, Worcestershire WR, UK). The relative hydrodynamic radius of MWCNT suspended in H₂O was measured using high throughput dynamic light scattering (HT-DLS, Dynapro^™ Plate Reader, Wyatt Technology, Santa Barbara, CA, USA).