Electrocatalytic Properties Of Chemical Modified Multi - Walled Carbon Nanotubes

Carbon nanotubes, which are also called as bucky tubes, are kinds of important carbon materials. Science 1991 first discovered by Janpanese scientist Iijima, carbon nanotubes exhibited unique structures and excellent electronic, thermodynamic and mechanical properties, and had been became the research focus in materials science, biology, physics, etc. This research topic also stimulated a lot of research interests. As a simple and efficient processing method, chemically-modification can enhance the sensitivity and selectivity of carbon nanotubes, and become the necessary part in purification, separation and application. The catalytic activities of different chemically-modified muti-walled carbon nanotubes（MWNTs） were investigated in the reduction of nitrobenzene and oxygen. Corresponding possible reaction mechanisms were proposed based on the experimental data. The main contents and innovations are shown as follows:（1） In the reduction of nitrobenzene, hydroxyl group modified MWNTs displayed the best catalytic activity, including the characteristic peak of nitrobenzene was high and sharp, background current was small and the detection limit was 0.08 μM. At the same time, the stability and reproducibility of hydroxyl group modified MWNTs were good, the catalytic activity was still very high after repeated used for 180 times. The mechanism of nitrobenzene was complex, and was founded to be dependent on the potential of scanning. Nitrobenzene was first generate phenylhydroxylamine, and phenylhydroxylamine can be oxidized to nitrosobenzene. Phenylhydroxylamine can be transformed to azobenzene, and azobenzene is reduced to hydrazobenzene. If the scanning potential is higher than 0.80 V, phenylhydroxylamine would generate p-aminophenol through the Bamberger rearrangement, and then p-aminophenol is oxidized to p-benzoquinoneimine.（2） The carboxyl groups modified MWNTs（MWNT-COOH） exhibited the best oxygen reduction activity, which was different with the reduction reaction of nitrobeneze. MWNT-COOH showed the most positive onset potential（-0.105 V） and the highest current density（-1.317 mA/cm²ï¼‰. Based on the experimental results in acidic electrolyte, it was believed that the functional groups could exist in different states under different pH conditions. In alkaline electrolyte,-COOH and-OH groups became-COO- and-O- after deprotonation reaction, respectively.-NH2 groups can become-NH₃⁺ after gaining H⁺ in acidic electrolyte. The results of density functional theory calculation were consistence with the experimental data. In addition, MWNT-COOH displayed an excellent the long-time electrocatalytic stability and the tolerance towards the test of methanol, ethanol and ethylene glycol compared that of commercial Pt/C catalyst.（3） The electrochemical reduction of nitrobenzene by two MnFe₂O₄ nanocrystals assemblies with different crystaline size were investigated. The experimental results indicated that MnFe₂O₄ nanocrystal assemblies diaplsyed catalytic activity in phosphate buffer solution, Na₂SO₄ and NaOH solution, and the peak currents reached the maximum in Na₂SO₄ solution. The electroreduction of nitrobenzene on MnFe₂O₄ nanocrystals assemblies was found to be closely related to the crystalline size and self-assembly of nanocrystals assemblies. MnFe-Na composed of smaller crystaline size performed higher electrochemical activity than that of MnFe-Ac.