Effect of Magnetic Metal Ions on Properties of Carbon Nanotube Slurry Dispersed by Sodium Carboxymethylcellulose
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摘要: 多壁碳纳米管（MWNTs）制备过程中残留的磁性金属催化剂可能对其在溶剂中的分散产生影响。本文通过将MWNTs分别分散到含有同一浓度金属离子（Fe3+，Fe2+，Ni2+，Co2+）的羧甲基纤维素钠（CMC）溶液中，制备了一系列MWNTs浆料。并系统性地探究了浆料的吸附量、拉曼光谱、zeta电位和吸附构象。结果表明，CMC/MWNTs浆料的分散稳定性按照Fe2+、Co2+、Ni2+、Fe3+的顺序依次降低。CMC在MWNTs表面的吸附量与吸附构象受CMC与金属离子之间螯合反应的控制，这决定了CMC/MWNTs体系的分散和稳定性。含有二价离子的浆料中，CMC能够形成一层均匀的膜，覆盖在MWNTs表面，CMC吸附量最大，MWNTs表面zeta电位最大，表现出较好的分散稳定性。Abstract: A detailed study of the dispersion, rheological and adsorption behaviors between multi-walled carbon nanotubes (MWNTs) and sodium carboxymethylcellulose (CMC) at different metal ions solutions were presented. The experimental results suggested that the chelation between metal ions and CMC governed the adsorption amount and adsorption conformation of CMC onto MWNTs, which had a great influence on the dispersion stability of MWNTs slurries. The MWNTs slurry with Fe2+ had smaller average size, lower viscosity and better stability, which led the slurry to evolving from shear-thinning fluid. It can be seen form UV adsorption experiment that the chelation between Fe3+ and CMC was stronger than that of other divalent ion. And the chelation increased with the increase of the radius of the divalent ion. Raman and Thermo-gravimetry (TGA) results showed that the adsorption amount of Fe3+ was lower, which provided a lower electrostatic repulsive force. In the slurry with divalent ions, adsorption amount of CMC onto MWNTs were higher in the order of Ni2+, Co2+ and Fe2+, providing higher repulsive force, larger zeta potential on MWNTs surface. That’s the reason why Fe2+ had better dispersion stability. The microstructures were measured by TEM. It was found that uniform CMC adsorption layers were formed on the surface of MWNTs with divalent ions. However, for the MWNTs with Fe3+, MWNTs were wrapped by CMC agglomerates, resulting in poor dispersion stability.
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图 1 金属离子对MWNTs浆料吸光度的影响
Figure 1. Effect of different kinds of ions on the absorbance of MWNTs suspensions by UV-Vis spectroscopy
图 2 金属离子对MWNTs浆料粒径分布的影响
Figure 2. Particle size distributions of MWNTs dispersed with CMC with different ions
图 3 不同金属离子存在条件下MWNTs浆料的流变曲线（a）流变行为曲线；（b）宾汉模型拟合
Figure 3. Rheological curves of MWCNTs slurry modified by CMC with different ions. a) relative viscosity; b) Herschel-Bulkley model fitting
图 6 不同金属离子存在条件下CMC/MWNTs的热重分析
Figure 6. Weight lose curves of CMC/MWNTs with different ions
图 7 不同金属离子存在条件下CMC/MWNTs的拉曼光谱
Figure 7. Raman spectra of CMC/MWNTs with different ions
图 8 不同金属离子对MWNTs浆料zeta电位的影响
Figure 8. Zeta potential of MWNTs suspensions with different ions
表 1 不同金属离子存在条件下MWNTs浆料的流变模型拟合参数
Table 1. Parameters for rheological models of MWNTs suspensions
Suspensions Parameter τy K n r2 CMC/MWNTs 11.184 1.662 0.565 0.999 Fe3/MWNTs 40.750 0.779 0.701 0.999 Fe2/MWNTs 31.029 1.045 0.656 1.000 Co/MWNTs 21.478 1.276 0.569 1.000 Ni/MWNTs 26.846 1.303 0.570 1.000 
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表 2 金属离子与CMC螯合物的UV-vis最大吸收波长与最大吸收峰值
Table 2. ABS and λmax of uv-vis for ions-CMC chelates
Ion λmax/nm Absorption Fe3+ 208 0.813 Fe2+ 204 0.263 Co2+ 202 0.410 Ni2+ 202 0.447
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