Studies On Functionalization Of Carbon-based Nanomaterials And Their Electroanalytical Properties

Since discovered in1991, CNTs have been intensively studied and havereceived a great deal of attention for their applications in electroanalysis, due totheir outstanding properties involved with one dimensional tubular-structure, highspecific surface area, high electronic conductivity, chemical/electrochemicalstability. However, CNTs are almost insoluble in all solvents due to strong Van DerWaals interactions that tightly hold them together, forming bundles, which destroytheir performances. Therefore, the choice of appropriate chemical functionalizationto enhance solubility in various solvents and to produce novel hybrid materials playan important role in the developing their property. This paper aims at preparationand electroanalytical application of functionalized carbon nanotubes and itsnanocomposite materials for construction electrochemical sensor with highsensitivity, fast response and good selectivity.In Chapter1, the structure and property, synthesis method, functional methodsand the application in electrochemical sensor of CNTs were introduced. In Chapter2, tunable polymerization of ionic liquid on the surfaces of multi-walled carbonnanotubes (MWCNTs) was achieved by a mild thermal-initiation-free radicalreaction of3-ethy-1-vinylimidazolium tetrafluoroborate in the presence ofMWCNTs and the thickness of PIL layer was controllable by tuning the ratio ofprecursor of IL. Successful modification of polymeric ionic liquid (PIL) onMWCNTs surfaces (PIL-MWCNTs) was demonstrated by thermogravimetricanalysis, scanning electron microscopy, transmission electron microscopy, fouriertransform infrared spectroscopy and X-ray photoelectron spectroscopy. The resulting PIL-MWCNTs possessed unique features of high dispersity in aqueoussolution due to positive imidazole groups along PIL chains, which were importantfor modification electrodes. The electrochemical properties of variousPIL-MWCNTs/GCEs were studied by cyclic voltammetry in Fe(CN)63-/4-solution.The result indicated that the increase of the effective electrochemical active surfaceby modification of PIL-MWCNTs and also implied the PIL thickness effected onthe charge transport at the electrode interface. The PIL-MWCNTs were used tomodify electrode to simultaneous determination of hydroquinone (HQ) andcatechol (CC). The experimental results indicated that pristine-MWCNTs modifiedelectrode also can oxide HQ and CC into two oxidation peaks, however, the twobroad oxide peaks dependence of each other. Thus, simultaneous determination ofHQ and CC could not be realized at pristine-MWCNTs. As for PIL-MWCNTsmodified electrode, based on the cation-π interaction between PIL-MWCNTs andHQ or CC, excellent discrimination ability towards HQ and CC and improvedsimultaneous detection performance were achieved. This sensor may be applied inenvironmental analysis. At the same time, the PIL-MWCNTs electrode was appliedto simultaneous determination of ascorbic acid, dopamine and uric acid. Theenlarged peak potential separation at PIL-MWCNTs/GCE coupled with thedramatic current increase could be attributed to the terminated-imidazole functionalgroups along the PIL chain, endowing the MWCNTs surface with a large numberof positive charges, which may be beneficial for the electrocatalytical separation ofthese biomolecules. The present study provides a great promise for practicalanalysis. In Chapter3, the ultra-fine Pt NPs were fabbricated on the surface ofPIL-MWCNTs as anchiriong points to bind with Pt precursors. The as-synthesizednanohybrids (Pt-PIL-MWCNTs) can catalyze the oxidation of the peroxidasesubstrate3,3,5,5-tetramethylbenzidine (TMB) in the presence of H2O2, exhibitinga blue color change in aqueous solutions, which could be used as a colorimetricmethod for H2O2determination.Compared with nature horseradish peroxidase (HRP), the Pt-PIL-MWCNTs can bear the high temperature and high concentrationof H2O2. Beside, with advantages of synthesis in low cost, tunability in catalyticactivities and a high stability against stringent conditions, the Pt-PIL-MWCNTsmay be a promising candidate as enzyme mimetics in bioanalysis. In Chapter4,1-Aminoanthraquinone (AAQ) was used as a binding agent that can absorb on theMWCNT surface based on the non-covalent π-π interaction between delocalized πelectrons of CNTs and these conjugated π aromatic molecules. The attractiveness ofthis π-π stacking approach is fundamentally related to its inherent experimentalfacility and simplicity. The AAQ can provide effectively-NH2binding sites forconfining smaller PtNPs on the surface of MWCNTs. Well-dispersed PtNPs withuniform size distribution centered at3.8nm were achieved on the surface ofAAQ-MWCNTs. Pt-AAQ-MWCNTs exhibited excellent electrocatalytic activitytowards O2and H2O2reduction, a possibility of fabricating a H2O2sensor based onPt-AAQ-MWCNTs was also demonstrated. Prospective applications ofPt-AAQ-MWCNTs may be extended to construction of other chem/biosensor onthe basis of its high catalytic activity towards O2and H2O2reduction.