Thermodynamic Determination of the Metal/Semiconductor Separation of Carbon Nanotubes Using Hydrogels
Thermodynamic Determination of the Metal/Semiconductor Separation of Carbon Nanotubes Using Hydrogels
复制标题
DOI：
10.1021/nn303985x
复制
发表时间：
2012-11-01
期刊：
影响因子：
17.1
通讯作者：
Kataura, Hiromichi
中科院分区：
文献类型：
--
作者：
Hirano, Atsushi;Tanaka, Takeshi;Kataura, Hiromichi
利用琼脂糖凝胶和Sephacryl等水凝胶和十二烷基硫酸钠等水凝胶对单壁碳纳米管进行金属/半导体分离是工业应用中最成功的技术之一。尽管这项技术最近有所改进，但人们对分离机制知之甚少。在这里，我们展示了在十二烷基硫酸钠存在的情况下，单壁碳纳米管可逆地吸附在水凝胶上。这些结果使我们能够考察吸附反应的热力学，从而阐明分离机理。用吸附的标准吉布斯自由能和允许吸附的水凝胶面积来描述碳纳米管在水凝胶上的吸附能力。在290-320K温度范围内，半导体SWCNTs的吸附自由能比金属SWCNTs的吸附自由能低0-12kJ/mol(例如，300K时琼脂糖凝胶的吸附自由能约为-4kJ/mol，Sephacryl的吸附自由能约为-9kJ/mol)，这使得金属/半导体分离成为可能。更重要的是，自由能的不同归因于吸附热焓的不同：金属碳纳米管的吸附热焓比半导体碳纳米管的高约70kJ/mol。因此，吸附热是利用水凝胶分离金属/半导体碳纳米管的一个重要参数。此外，热力学参数取决于水凝胶的类型和表面活性剂的浓度，这很可能是水凝胶和表面活性剂在特定条件下产生不同分离的原因，例如手性选择分离或直径选择分离。
The metal/semiconductor separation of single-wall carbon nanotubes (SWCNTs) using hydrogels, such as agarose gel and Sephacryl, together with sodium dodecyl sulfate is one of the most successful techniques necessary for industrial applications. Despite recent improvements in the technique, little is known about the separation mechanism. Here, we show that SWCNTs are reversibly adsorbed onto hydrogels in the presence of sodium dodecyl sulfate. The results enabled us to examine the thermodynamics of the adsorption reaction and thereby elucidate the separation mechanism. The adsorbability of SWCNTs onto the hydrogels was described by the standard Gibbs free energy for the adsorption, as well as the area of the hydrogels allowing the adsorption. We demonstrated, for the first time, that the free energy of adsorption for semiconducting SWCNTs was 0-12 kJ/mol lower than that for metallic SWCNTs in the temperature range of 290-320 K (e.g., ca. -4 kJ/mol for the agarose gel and ca. -9 kJ/mol for Sephacryl at 300 K), which permits metal/semiconductor separation. Importantly, the difference in the free energy was attributed to the difference in the enthalpy of adsorption: the enthalpy of adsorption of metallic SWCNTs was ca. 70 kJ/mol higher than that of semiconducting SWCNTs. Thus, the enthalpy of adsorption was found to be an important parameter in the metal/semiconductor separation of SWCNTs using hydrogels. In addition, the thermodynamic parameters depended on the hydrogel type and the surfactant concentration, which is most likely why under certain conditions hydrogels and surfactants produce different separations, e.g., chirality-selective or diameter-selective separation.