Abstract

Adsorption is known as the best technique to remove dyes from waste water, and the choice of adsorbent is the most important factor. In this regard, some commercial porous materials have been applied for a long time as popular adsorbents for dye adsorption. However, the search for new classes of porous materials is still attractive to researchers. Recently, metal-organic frameworks are seen to be promising candidates as adsorbents for dyes due to their large surface area, ordering, and flexible structure. There are some possible mechanisms for the dye adsorption in water performed on metal-organic frameworks, including the electrostatic interaction forming attractive charge of dye molecules and adsorbents, π–π stacking of organic rings from dye and metal-organic frameworks, hydrogen bonding between the dye and hydroxyl group of the metal-organic frameworks, hydrophobic interaction, acid-base interaction and effect of framework structure. Among them, the electrostatic attraction mechanism plays an important role in dye adsorption on MOFs, highlighting differences as compared to traditional adsorbents in this field. This work is the first detailed investigation into the effect of electrostatic attraction mechanism in dye adsorption on UiO-66 and their modifications. Two samples of Co/UiO-66 and H⁺/UiO-66 were prepared under normal stirring and heating conditions to increase the positive charge of the surface. The characterization using powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and FTIR indicated the existence of proton on UiO-66, while Raman spectroscopy and inductively coupled plasma mass spectrometry (ICP-MS) confirmed the successful addition of cobalt into the UiO-66 structure at the amount of about 0.6 wt %. Results obtained for methyl orange (MO) adsorption on the surface have shown enhanced adsorption capacity for both Co-UiO-66 and H⁺/UiO-66 as compared to parent UiO-66. Moreover, the experiments with highly selective removal of anionic dye as compared to cationic dye were performed and explained in detail for mixed dye solutions of MO with methylene blue (MB), indicating the important role of electrostatic attraction mechanism. Notably, it is shown that the addition of Co to UiO-66 results in a higher effect of electrostatic interaction than that of H⁺.

中文翻译：

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染料在UiO-66上的吸附：静电吸引机制的重要性

摘要

吸附是从废水中去除染料的最佳技术，而吸附剂的选择是最重要的因素。在这方面，一些商业多孔材料作为染料吸附的流行吸附剂已长期使用。但是，寻找新型的多孔材料仍对研究人员有吸引力。近来，由于其表面积大，有序且结构灵活，金属有机骨架有望成为染料的吸附剂。在金属-有机骨架上进行染料吸附有一些可能的机制，包括静电相互作用形成了染料分子和吸附剂的吸引电荷，染料和金属-有机骨架从有机环的π-π堆积，染料与金属-有机骨架的羟基之间的氢键，疏水相互作用，酸碱相互作用和骨架结构的影响。其中，静电吸引机制在MOF上的染料吸附中起着重要作用，与该领域的传统吸附剂相比，突出了差异。这项工作是对静电吸引机制在染料吸附到UiO-66上及其修饰作用方面的首次详细研究。Co / UiO-66和H的两个样品 这项工作是对静电吸引机制在染料吸附到UiO-66上及其修饰作用方面的首次详细研究。Co / UiO-66和H的两个样品 这项工作是对静电吸引机制在染料吸附到UiO-66上及其修饰作用方面的首次详细研究。Co / UiO-66和H的两个样品在正常的搅拌和加热条件下制备⁺ / UiO-66以增加表面的正电荷。使用粉末X射线衍射（XRD），扫描电子显微镜（SEM）和FTIR进行的表征表明UiO-66上存在质子，而拉曼光谱和电感耦合等离子体质谱（ICP-MS）证实成功添加了钴以约0.6重量％的量加入UiO-66结构。在表面上吸附甲基橙（MO）的结果表明，对Co-UiO-66和H ^+的吸附能力均增强/ UiO-66与父级UiO-66相比。此外，进行了与阳离子染料相比高度选择性去除阴离子染料的实验，并详细说明了MO与亚甲基蓝（MB）的混合染料溶液，表明了静电吸引机制的重要作用。值得注意的是，已表明，向UiO-66中添加Co比H ⁺具有更高的静电相互作用效果。