Functionalization Of Carbon Nanotubes With Polymer And Their Application In Catalysis And Biology

Since their discovery, carbon nanotubes (CNTs) have attracted great attentions allover the world, due to their intrinsic structures (e.g. large aspect ratio and chirality),outstanding properties (e.g. electrical, mechanical, optical properties) as well as theirpromise potential applications in the area of material chemistry. However, CNTs arenot solubilized in almost any solvents, which hinderes their applications. So, it is veryimportant to functionalize the carbon nanotubes in order to improve their dispersibilityin solvents and matrics. Various surface functionalization methods have beeninvestigated, including physical bonding and chemical bonding. The chemicalfunctionalization of CNTs can not only improve their solubility, but also afford theirnovel properties. The in situ radical polymerization was a simple and easy way tofunctionalize the CNTs, but a lot of monomer and solvent only functionalizedmilligram CNTs with the reported methods. In this dissertation, the CNTs werefunctionalized by hydrophobic or hydrophilic polymer through in situ precipitationpolymerization with less monomer and solvent. The mechanism of functionalization ofCNTs was also discussed. The functionalized CNTs were successfully used to tracelymph nodes and load metal nanoparticles for selective hydrogenation of citral. Theimportant results obtained are as follow:(1) Firstly, we derived the single-walled carbon nanotubes (SWNTs) with in situprecipitation polymerization. The structure of functionalized SWNTs wascharacterized by Raman spectroscopy, UV-vis spectroscopy, HRTEM and AFM,which demonstrated that the SWNTs were successfully grafted by polymer. Theprocess of functionalization of SWNTs by in situ precipitation polymerization is like a"fishing" process. The SWNTs act as "fishhooks" and the "living" polymer radicals are "fish", which are enthalpically favored to absorb onto the surface of SWNTs andcontinue to propagate until all the active sites are consumed. So the SWNTs can bederived with less solvent and monomers, e. g. we demonstrated to graft 1 g of SWNTsby～20 wt% poly(methyl methacrylate) in 100 mL methanol/water (1/4 by volume)with monomer concentration as low as 5 mg/mL. Although the SWNTs are higheractive, their price is great higher than that of MWNTs, so we try to functionalize theMWNTs with the same method. The experiments demonstrated that the MWNTs weresuccessfully derived by hydrophobic or hydrophilic polymer. The promise ofsynthesizing gram-scale functionalized CNTs in a small amount of solvent may greatlyimprove the ability to scale up the preparation of functionalized CNTs.(2) From references, we know that the CNTs are excellent biomedical materials afterhydrophilic functionalization. So we functionalized the MWNTs by PAA in a poorsolvent of PAA but a good solvent of AA. The chain length of PAA grafted onMWNTs was controlled by functionalization of MWNTs in different solvents. Thedifferent degrees of sidewall functionalized MWNTs were separated by differentstrengthes of centrifugation. So the MWNTs with high grafted density of PAA chainswere obtained. These functionalized MWNTs could well be dispersed in water, NaClaqueous solution (0.9 wt%) and standard solution for cell cultures. The cellular toxicityof these MWNTs was low. In our experiment, we found that the hydrophilic MWNTswas a good lymph node tracer. The cellular experiment demonstrated that the plasmidDNA could be delivered into cell and transfected efficiently. These mean that thehydrophilic MWNTs could be uesed to treat lymph node metastases. This type ofMWNTs also could be considered as the potential candidate supporter for anti-cancerdrug to the regional lymph nodes.(3) For a long time, the CNTs are ranked as the potential candidate of excellentsupporter of metal catalyst, due to their inert and large aspect ratio. In this dissertation,the functionalized MWNTs were decorated by different density, size, shape and crystalPt nanoparticles with electroless deposition method through addition of some special ions, such as Cu²⁺ or NO₃^-. The Pt/MWNTs composites were used to selectivehydrogenation of citral. It was found that the irregular polycrystal Pt nanoparticles hada high activity (conversion＞90%) at low temperature (60℃) and monohydrogenationselectivity (ca. 100%), but the stereoselectivity (ratio of geraniol/nerol) was lower (1.9).The single crystal tetra- and octahedrons Pt nanoparticles had pretty highstereoselectivity (5.4), but it was lower (2.2) for the single crystal tetra- and octapodsPt nanoparticles. It was found that tetra- and octahedral Pt nanoparticles were allbounded by {111} facets, but they were deformed in tetrapods and octapods. All ofthese suggest that the close-packed {111} facets have stereoselectivity for geraniol bysteric hindrance. The function of PAA grafted on MWNTs in deposition of Ptnanopaerticles was demonstrated and a deposition mechanism was proposed.