Abstract

The laws and mechanisms of adsorption of Cu(II) ions by well characterized and oxidized N‑doped multi-walled carbon nanotubes (N-CNTs) are discussed. The samples were synthesized by catalytic chemical vapour deposition method using n-butylamine as a carbon source and their surface was functionalized by oxidation with mixture of concentrated H₂SO₄ and HNO₃. The morphology, chemistry and charge of surface groups were characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy and micro-electrophoresis methods. It has been shown that: adsorption of Cu(II) reached equilibrium value within 60 min; the degree of extraction of these ions from the solution increased with its dilution; adsorption resulted in a moderate decrease in the suspension pH for as-prepared N-CNTs (1.5 pH unit) and its considerable lowering for the oxidized sample (up to 2.5 pH unit); the adsorption isotherms can be described by the Langmuir model and the plateau amounts of adsorption (28–35 mg/g) were almost the same for both as-prepared and oxidized samples; at pH 6.5 and higher a sharp increase in adsorption was observed which was attributed to hydroxides precipitation. The spectroscopic, adsorption, electrophoretic and pH measurements data showed that below pH of hydroxide precipitation, the major mechanism of adsorption by as-prepared N-CNTs is the donor-acceptor interaction between the free electron pair of N atoms incorporated into nanotubes lattice and vacant d orbital of the adsorbing Cu(II) ions. For the oxidized N-CNTs ion-exchange processes with a release of H⁺ ions play also a role.

中文翻译：

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制备和氧化的多壁N掺杂碳纳米管对Cu（II）吸附的比较研究

摘要

讨论了良好表征和氧化的N掺杂多壁碳纳米管（N-CNT）吸附Cu（II）离子的规律和机理。以正丁胺为碳源，通过催化化学气相沉积法合成样品，并通过浓H ₂ SO ₄和HNO _3的混合物的氧化对它们的表面进行功能化。。通过透射电子显微镜，X射线光电子能谱，傅立叶变换红外光谱和微电泳方法对表面基团的形貌，化学性质和电荷进行了表征。结果表明：60min内Cu（II）的吸附达到平衡值；这些离子从溶液中的提取程度随着稀释而增加；吸附导致所制备的N-CNT的悬浮液pH适度降低（1.5 pH单位），而氧化样品的悬浮液pH显着降低（最高2.5 pH单位）；吸附等温线可以用Langmuir模型描述，制备的和氧化的样品的吸附平台量（28-35 mg / g）几乎相同；在pH 6。在5和更高的值下，观察到吸附的急剧增加，这归因于氢氧化物的沉淀。光谱，吸附，电泳和pH测量数据表明，在氢氧化物沉淀的pH值以下，制备的N-CNT吸附的主要机理是掺入纳米管晶格中的N原子的自由电子对与空位之间的供体-受体相互作用。吸附Cu（II）离子的d轨道。对于氧化的N-CNT，释放H ⁺离子的离子交换过程也起作用。