Abstract

The work considers the processes of modifying the surface of multiwalled carbon nanotubes with various polar groups: carboxyl, alcoholic hydroxyl, and quaternary ammonium salt. A procedure is developed using an oxidizing mixture of hydrogen peroxide, nitric acid, and sulfuric acid for the carboxylation of carbon nanotubes at a temperature of 70°C, which minimizes the formation of amorphous carbon and increases the concentration of carboxyl groups on the surface to 5.5 wt %. Tubes with a surface modified with a quaternary ammonium salt are obtained from carboxylated carbon nanotubes by reaction with triethanolamine. The modification of carbon nanotubes with ethyl hydroxyl groups is carried out with the participation of a free-radical initiator in an ethanol medium. The initial defects of nanotubes determine the number and nature of the defects at which chemical bonding occurs during functionalization, regardless of the method of nanocarbon material processing. The thermal–oxidative stability of the initial and modified carbon nanotubes in air is explored. The initial nanotubes are the most stable; they maintain their properties even when heated up to 520°C in air. For modified nanotubes, the thermal stability decreases in the series multiwalled nanotubes with carboxyl groups on the surface, multiwalled nanotubes with alcoholic hydroxyl groups, and multiwalled nanotubes modified with a quaternary ammonium salt, the oxidation of which begins at 400°C. The grafting of alcohol hydroxyl groups onto the surface of multiwalled carbon nanotubes is of considerable interest for obtaining an adsorption material with a developed surface, capable of covalently binding metal ions due to hydroxyl groups, similarly to complexing agents such as ethylene glycol or pyrocatechol. Carbon nanomaterials modified with polar groups exhibit good adsorption properties with respect to heavy metal ions. The degree of extraction of zinc and copper ions in the case of carboxylated nanotubes reaches 98%.

中文翻译：

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多壁碳纳米管的表面改性以赋予技术性能

摘要

这项工作考虑了用各种极性基团（羧基、醇羟基和季铵盐）修饰多壁碳纳米管表面的过程。开发了一种使用过氧化氢、硝酸和硫酸的氧化混合物在 70°C 温度下对碳纳米管进行羧化的程序，该程序最大限度地减少了无定形碳的形成并增加了表面羧基的浓度5.5重量％。通过与三乙醇胺反应，由羧化碳纳米管获得表面经季铵盐修饰的管。碳纳米管的乙基羟基修饰是在乙醇介质中自由基引发剂的参与下进行的。无论纳米碳材料的加工方法如何，纳米管的初始缺陷决定了功能化过程中发生化学键合的缺陷的数量和性质。研究了初始碳纳米管和改性碳纳米管在空气中的热氧化稳定性。最初的纳米管是最稳定的；即使在空气中加热至 520°C，它们仍能保持其特性。对于改性纳米管，表面带有羧基的多壁纳米管、带有醇羟基的多壁纳米管和季铵盐改性的多壁纳米管系列的热稳定性下降，其氧化在400℃开始。将醇羟基接枝到多壁碳纳米管的表面上对于获得具有发达表面的吸附材料具有相当大的意义，该吸附材料能够由于羟基而共价结合金属离子，类似于络合剂例如乙二醇或邻苯二酚。极性基团修饰的碳纳米材料对重金属离子表现出良好的吸附性能。羧化纳米管中锌离子和铜离子的萃取率达到98%。