Functionalization Of Carbon Nanotube And Its Applications

This thesis investigated rapid functionalization of SWNTs and its applications. Extensive studies were made on electrocatalytic activities of 1,2-Naphthoquinone modified carbon nanotube toward the oxidation of NADH, on preparation and characterization of room temperature ionic liquid/single-walled carbon nanotubes nanocomposite and its application in direct electrochemistry of heme-containing proteins/enzymes, on functionalization of single-walled carbon nanotube with poly(nile blue A) and its application to dehydrogenase-based biosensor. The main results of this thesis were expressed in detail as following:1. It was reported that SWNTs was functionalized with the electroactive Nile Blue (NB), which was a phenoxazine dye, by a method of adsorption to form a NB-SWNTs nanocomposite. The NB-SWNTs nanocomposite was characterized by several spectroscopic techniques, for example UV-Vis, FTIR, Raman spectroscopy and SEM et al., and the results showed that NB can rapidly and effectively be adsorbed on the surface of SWNTs with high stability without changing the native structure of NB and the structure properties of SWNTs. Moreover, it was shown that the dispersion ability of SWNTs in aqueous solution had a significantly improvement after SWNTs functionalized with NB even at a level of high concentration, for example 5 mg NB-SWNTs per 1 mL H₂O. The NB-SWNTs /GC electrode was fabricated by modifying NB-SWNTs nanocomposite on the GC electrode surface and its electrochemical properties were investigated by cyclic voltammetry. The cyclic voltammetric results indicated that SWNTs could improve the electrochemical behavior of NB and greatly enhance its redox peak currents. While the NB-SWNTs /GC electrode exhibited a pair of well-defined and nearly symmetrical redox peaks with the formal potential of (-0.422±0.002) V (vs. SCE, 0.1 mol/L PBS, pH 7.0), which was almost independent on the scan rates, for electrochemical reaction of NB monomer, the redox peak potential of NB polymer located at about -0.191 V. The experimental results also demonstrated that NB and SWNTs could synergistically catalyze the electrochemically oxidation of NADH and NB- SWNTs exhibited a high performance with lowing the overpotential of more than 560 mV. The NB-SWNTs /GC electrode could effectively sense the concentration of NADH, which was produced during the process of oxidation of substrate (for example ethanol) catalyzed by dehydrogenase (for example alcohol dehydrogenase).2. It was reported that SWNTs was functionalized with the electroactive species of Nq by a method of adsorption to form Nq-SWNTs nanocomposite. The Nq-SWNTs was characterized by spectroscopic techniques, for example UV-Vis, FTIR and SEM et al., and the results showed that Nq can rapidly and effectively be adsorbed on the surface of SWNTs with high stability. Moreover, it was shown that the dispersion ability of SWNTs in aqueous solution had a significantly improvement after SWNTs functionalized with Nq. The Nq-SWNTs /GC electrode was fabricated by modifying Nq-SWNTs nanocomposite on the GC electrode surface and its electrochemical properties were investigated by voltammetry, which indicated that SWNTs could improve the electrochemical behavior of Nq and greatly enhanced its redox peak currents. The Nq-SWNTs /GC electrode exhibited a pair of well-defined and nearly symmetrical redox peaks with the formal potential of -87.3±4.5 mV (vs. SCE, 0.1 mol/L PBS, pH 7.0), which was almost independent on the scan rates. The experimental results also demonstrated that Nq and SWNTs could synergistically catalyze the electrochemically oxidation of NADH and Nq-SWNTs exhibited a high performance with lowing the overpotential of more than 510 mV.3. This communication describes the formation and possible electrochemical application of a novel nanocomposite based on the SWNTs and RTILs of [bmim]BF₄ and [bmim]PF₆. The nanocomposite ([bmim]BF₄-SWNTs, and [bmim]PF₆-SWNTs) was formed by simply grinding of the SWNTs with the RTILs. The results of the X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy indicated that the nanocomposites were formed by adsorption of imidazolium ion on the surface of SWNTs via the "cation-Ï€" interaction, and scanning electron microscopic (SEM) images showed that the adsorption of imidazolium ion could significantly enhance the dispersed ability of SWNTs in water and [bmim]BF₄-SWNTs (or [bmim]PF₆-SWNTs) composite could uniformly cover on the surface of glassy carbon (GC) electrode forming RTILs-SWNTs/GC modified electrode with a high stability. The modified electrodes were characterized by used to study the electrochemical impedance of two different kinds of redox couple of Fe(CN)₆^3-7Fe(CN)₆^-4 and Ru(NH₃)₆³⁺/Ru(NH₃)₆²⁺, and also to investigate the cyclic voltammetric responses of two important neutrotransmitters of dopamine (DA) and ascorbic acid (AA). The RTILs-SWNTs composite could be readily used as a matrix to immobilization heme-containing proteins/enzymes (myoglobin, cytochrome c, and horseradish peroxidase), and the UV-Vis spectroscopic results indicated that the proteins/enzymes retained their nature structure in the composites. The voltammetric results showed that heme-containing proteins/enzymes displayed a pair of well-defined, stable redox peak ascribing to their direct electron-transfer reaction. RTILs on the surface of SWNTs couldn't promote the direct electron-transfer of heme-containing proteins/enzymes, but the positive charge possessing by imidazolium ion played an significantly effect on the electrochemical parameters, such as redox peak separation and the value of the formal potentials et al., of the electron-transfer reaction for non-neutral species in the studied solution. The further results demonstrated that the heme-containing proteins/enzymes entrapped in RTILs-SWNTs composites could still retain their bioelectrocatalytic activity to the reduction of oxygen and hydrogen peroxide.4. SWNTs were functionalized with poly(nile blue A) and forming a new type of nanocomposites of poly(nile blue A)-SWNTs (PNb-SWNTs) by electropolymerization of Nb monomer on the surface of SWNTs/GC electrode using cyclic voltammetry. The scanning electron microscopy (SEM), ultraviolet-visible (UV-Vis), cyclic voltammerty, and electrochemical impedance spectroscopy (EIS) were used to characterize the PNb-SWNTs nanocomposites. The cyclic voltammetric results indicated that PNb-SWNTs nanocomposites could catalyze the electrochemical oxidation of NADH at a very low potential (ca.(?)80 mV) and lead to a substantial decrease in the overpotential by more than 700 mV compared with bare glassy carbon (GC) electrode. A biosensor, ADH-PNb-SWNTs/GC, was developed by immobilization ADH on the PNb-SWNTs/GC electrode surface. The biosensor showed the electrocatalytic activity toward the oxidation of ethanol with a good stability, reproducibility and higher biological affinity. Under an optimal conditions, the biosensor could be used to detection ethanol, representing a typical characteristic of Michaelis-Menten kinetics with the apparent Michaelis-Menten constant of K_M^app～6.30 mM, with a linear range span the concentration of ethanol from 0.1 to 3.0 mM (with correlation coefficient of 0.998), and the detection limit of～50μM (at a signal-to-noise ratio of 3).