Joining and Welding Research Institute, Osaka University, Osaka 5670047, Japan.
Division of Environmental Engineering Science, Graduate School of Science and Technology, Gunma University, Gunma 3768515, Japan.
J Hazard Mater. 2023 Apr 5;447:130803. doi: 10.1016/j.jhazmat.2023.130803. Epub 2023 Jan 19.
Water pollution by dyes is one of the biggest environmental problems. Adsorption technology has been widely used in wastewater treatment. In this work, high-entropy concept is used to design surface defective hydroxides realizing the rapid removal of dyes from water. Multi-element hydroxides (MEHs) containing three (CoMnNi, MEH-Ternary), four (CoMnNiZn, MEH-Quaternary), and five (CoMnNiZnFe, MEH-Quinary) metal elements are successfully synthesized through a polyol process. These as-synthesized MEHs are composed of nanosheets with a brucite-like structure. Along with the increase in compositional complexity (i.e., configurational entropy), the thickness of the nanosheets in these MEHs decreases, while the degree of surface defects increase. These surface defects are probably the active sites for anionic dyes adsorption, suggesting rapid adsorption kinetics with shortened diffusion path length. For MEH-Quinary in 0.2 mM Congo red (CR) and MEH-Ternary in 0.4 mM methyl orange (MO) aqueous solutions, respectively, high removal efficiency > 99.0% is achieved in the first 30 s. Their pseudo-second-order rate constants are two orders of magnitude higher than that of activated carbon and hydrotalcite. MEH-Quinary has maximum CR and MO adsorption quantity of 546.4 and 404.9 mg g, respectively, by Langmuir model. The MEH-Quinary is also a potential electrocatalyst for oxygen evolution reaction.
水污染是最大的环境问题之一。吸附技术已广泛应用于废水处理。在这项工作中，高熵概念被用于设计表面缺陷的氢氧化物，实现了从水中快速去除染料。通过多元醇工艺成功合成了含有三种（CoMnNi，MEH-三元）、四种（CoMnNiZn，MEH-四元）和五种（CoMnNiZnFe，MEH-五元）金属元素的多元氢氧化物（MEHs）。这些合成的 MEHs 由具有水滑石结构的纳米片组成。随着组成复杂性的增加（即构型熵），这些 MEHs 中纳米片的厚度减小，而表面缺陷的程度增加。这些表面缺陷可能是阴离子染料吸附的活性位点，表明吸附动力学迅速，扩散路径长度缩短。在 0.2 mM 刚果红（CR）和 0.4 mM 甲基橙（MO）水溶液中，MEH-五元和 MEH-三元分别在 30 s 内达到 >99.0%的高去除效率。它们的准二级速率常数比活性炭和水滑石高两个数量级。MEH-五元对 CR 和 MO 的最大吸附量分别为 546.4 和 404.9 mg g，符合 Langmuir 模型。MEH-五元还是一种潜在的析氧反应电催化剂。
