Studies on carboxylation of multi-walled carbon nanotubes and their applications for hydrogen peroxide and glucose sensing

• Main Authors: Yu Chen Lin, 林育城
• Other Authors: M. Y. Hua
• Format: Others
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/53446658508229997422

博士 === 長庚大學 === 化工與材料工程學系 === 100 === The goal of this dissertation is to prepare and characterize electrochemical sensors based on multiwalled carbon nanotube (MWCNT) derivatives with high performance and excellent stability for detection of hydrogen peroxide (H2O2) and glucose. At present, this research has been developed a polyani-line/carboxy-functionalized multiwalled carbon nanotube (PAn/MWCNTCOOH) nanocomposite by blending the emeraldine base form of polyaniline (PAn) and carboxy-functionalized multiwalled carbon nanotubes (MWCNT) in dried dimethyl sulfoxide (DMSO) at room temperature. The structure, morphology and conductivity of PAn/MWCNTCOOH nanocomposites were characterized by Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), Field-emission scanning electron microscopy (FE-SEM) and the four-point probe method. The possible dopant behavior of this nanocomposite is also discussed. The main characteristic peaks of PAn for this nanocomposite shifted to lower frequency, which was attributed to mainly as a result of the protonation of the PAn with the carboxyl group and the radical cations of the MWCNT fragments by FT-IR. The doping level (i.e., the amount of radical cation nitrogen and iminium ions) for PAn within PAn/MWCNTCOOH nanocomposite was calculated to be approximately 34% by XPS. The diameters of the PAn/MWCNTCOOH nanocomposites increased to 45–75 nm by FE-SEM and the conductivity of the resulting PAn/MWCNTCOOH was 3.6  10–3 S/cm by four-point probe. Horseradish peroxidase (HRP) was immobilized within the PAn/MWCNTCOOH nanocomposite modified Au (PAn/MWCNTCOOH/Au) electrode to form HRP/PAn/MWCNTCOOH/Au for use as a H2O2 sensor. The adsorption between the negatively charged PAn/MWCNTCOOH nanocomposite and the positively charged HRP resulted in a very good sensitivity to H2O2 and an increased electrochemically catalytical current during cyclic voltammetry. The HRP/PAn/MWCNTCOOH/Au electrode exhibited a broad linear response range for H2O2 concentrations (86 M–10 mM). This sensor exhibited good sensitivity (194.9 μA/mM-cm2), a fast response time (2.9 s), and good reproducibility and stability at an applied potential of 0.35 V. In addition, a new approach to synthesising 1-one-butyric ac-id-functionalised multi-walled carbon nanotubes (MWCNTs-BA) is presented involving the surface modification of multi-walled carbon nanotubes (MWCNTs) via a Friedel-Crafts chemical oxidative reaction using succinic anhydride in aluminium chloride. The 1-one-butyric acid (BA) groups formed on the sidewalls of the MWCNTs as confirmed by FT-IR, XPS and Raman spectroscopy. The MWCNTs-BA disperses homogeneously in water and exhibits very good solubility. The percentage of BA groups in the MWCNTs-BA was 7.80 mol% as determined by a simple acid-base titration method. The electrical conductivity, morphology and structure of the MWCNTs-BA were characterized with a four-point probe, FE-SEM, transmission electron microscopy (TEM) and X-ray diffraction (XRD), respectively. However, the conductivity of the resulting MWCNTs-BA11 was 1.8  10–3 S/cm by four-point probe. The MWCNTs-BA11 surfaces were irregular and rough with diameters of 45–65 nm by FE-SEM and TEM. The results showed that BA groups were covalently bonded to the sidewalls of the MWCNTs, leading to an ordered space between the tubes by XRD. Finally, the sensor created by the immobilization of glucose oxidase (GOD) onto the surface of MWCNTs-BA was sensitive toward glucose over a linear range from 10 M to 2.5 mM with a correlation coefficient of 0.999 (n = 5), and it showed good sensitivity (23.5 μA/mM-cm2), enzyme affinity, reproducibility and storage stability. This immobile MWCNTs-BA matrix acts as an electron bridge between the enzyme molecules and the electrode, and it has the potential to allow the construction of useful sensors through enzyme immobilization.