Quantitative Determination Of The Functional Groups On Carbon Nanotubes

Carbon nanotubes, discovered by Iijima in 1991, have attracted much attention in the fields of chemistry, physics, biology and material science due to their unique structure and physical and chemical properties.Many technologies have been applied in CNTs' preparation, chemical and physical modification, morphological characterization and application. Though there have been many technologies to characterize CNTs qualitatively, for example, TEM, SEM, AFM and Raman spectra, quantitative methods are dropped behind. Moreover papers reported are mostly focused on assays of SWNTs, systemic quantitative research for MWNTs has not been appeared so far.In this research carboxylic C₆₀, carboxylic MWNT and amino MWNT were firstly synthesized. The functional groups on CNTs were then quantified with three methods: acid-base titration, weight method and De-Fmoc method, and the results were compared by their accuracy, precision and error factors.Acid-base titration method was used to quantify carboxylic groups on many carbon materials since 1960s. The veracity of this method could not be validated because the carboxylic groups on these materials are uncertain. Based on Hu' s acid-base titration method for the quantitative assay of SWNTs, a modified method was applied for the determination of MWNTsand the -COOH density on carboxylic C60 in oeder to validate the method' s veracity. The total acid density, including -COOH, -OH and lactone, was also determined.We compared the effects of different acidization methods through this optimized titration method. From the results of shortened reaction time experiment, we can make conclusion: most carboxylic groups are on the surface of CNTs and easy to react with base solution.Using the reaction between carboxylic SWNTs and octadecylamine in 2005. Marshall determined the density of carboxylic groups on SWNTs according to the weight difference before and after the reaction. We applied this method for the determination of density of carboxylic groups on MWNTs. The results showed that the content of carboxylic groups detected are less than theoretic value, which maybedue to the complicated environment on MWNTs surface and the incomplete solid-liquid reaction.De-Fmoc method is a mature quantitative method in solid-phase synthesis, which is accurate and easy to operate and monitor the reaction process. Li Jiang determined the density of amino groups on GCNFs using this method. We applied this method to determine the amino groups on MWNTs and got the same conclusion with Li Jiang. The results indicated that this method is hopeful to be analternative method to quantify the amino groups on functional CNTs with high precision, and capable of monitoring the modification reaction.In conclusion, this thesis first systemically studied the quantitative analytical methods of functional groups on CNTs, we found that acid-base titration method is so far the most accurate method to quantify the carboxylic groups on CNTs. and De-Fmoc method can simply and accurately determine the density of amino groups on functional CNTs.