Synthesis And Properties Of Chitosan-grafted Carbon Nanotubes

Carbon nanotubes/chitosan (CNT/CS) composite has biologic and optoelectronic function. Based on attractive biocompatibility, biodegradability and non-toxicity of CS, many researchers explored the possibility of CS as platforms in biological field. CNT/CS composites not only are hopeful to improve the dispersibility and solubility of CNT by the hydrophilicity of biopolymer, but also could endue some biologic ability for CNT that can provide an approach for the application of CNT.A novel Chitosan-grafted multiwalled carbon nanotubes (CS-g-MWCNT) was prepared through covalently grafting a biocompatible polymer CS onto the surfaces of MWCNT. On the basis of Fourier transform infrared spectroscopy (FT-IR), we can conclude that the CS was covalently grafted onto MWCNT. Ultraviolet-visible spectroscopy (UV-vis) shows a sharp absorption peak in about 265 nm appeared which can be attributed to the characteristic absorption of MWCNT. Interestingly, the observed absorption peak in CS-g-MWCNT solution depends on the solution concentrations in a linear fashion, obeying the Lambert-Beer's law. A core-shell nanostructure can be observed by transmission electron microscopy (TEM), indicating that the nanotubes were coated with polymer chains. Thermogravimetry analysis (TGA) data furnish quantitative information on the degree of functionalization. The covalent modification overcomes the issues of poor interfacial bonding and results in stable dispersibility of MWCNT in some diluted organic acid (formic, benzoic, acetic, etc.).The electrochemical properties of the CS-g-MWCNT were characterized by an electrodeposition method that involves depositing it on an Au electrode. The porous microstructure of the CS-g-MWCNT modified electrode was observed by scanning electron microscopy (SEM) which is contrast to the non-covalent modification of MWCNTs with CS (CS/MWCNT). The excellent electrocatalytic ability of the CS-g-MWCNT modified electrode towards hydrogen peroxide is applicable to the development of oxidase-based amperometric biosensors. As an example, an amperometric glucose biosensor based on the enzyme electrode with CS-g-MWCNT modified electrode was fabricated. The glucose oxidase (GOD) was cross-linked and immobilized on the electrode surface by the use of glutaraldehyde. The electron could transfer more easily between electrode surface and bioactive center of GOD because of the special structure of CS-g-MWCNT. The CS-g-MWCNT biosensor has higher sensitivity and wider linear response range than the CS/MWCNT biosensor.The CS-g-MWCNT in poly(vinyl alcohol) (PVA) matrix was electrospun into nanofibers with a mean diameter of 232±85 nm. Raman spectroscopy shows the existence of MWCNT and the absorption peak in CS-g-MWCNT/PVA electrospun nanofibers depends on the concentrations of CS-g-MWCNT. Scanning electron microscopy (SEM) was used to characterize the morphologies of the CS-g-MWCNT nanofibers and the results show that the CS-g-MWCNT/PVA nanofibers have uniform diameter distribution in contrast to CS/MWCNT/PVA nanofibers. The excellent electrochemical properties of the CS-g-MWCNT/PVA nanofibers attribute to high surface/volume ratio which is applicable to the development of biosensors.