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化学进展 2022, Vol. 34 Issue (7): 1524-1536 DOI: 10.7536/PC220309 前一篇   后一篇

• 综述 •

离子溶液中的芳香环:反常化学计量比的二维晶体和其铁磁性

杨一舟1, 彭兵权2,3, 雷晓玲1, 方海平1,2,3,*()   

  1. 1.华东理工大学物理学院 上海 200237
    2.中国科学院大学温州研究院 温州 325001
    3.瓯江实验室 温州 325000
  • 收稿日期:2022-03-08 修回日期:2022-05-30 出版日期:2022-07-24 发布日期:2022-06-20
  • 通讯作者: 方海平
  • 基金资助:
    国家自然科学基金项目(11974366); 中央高校基本科研业务费专项资金资助
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Aromatic Rings in Ion Soultions: Two-Dimensional Crystals of Unconventional Stoichiometries and Ferromagnetism

Yizhou Yang1, Bingquan Peng2,3, Xiaoling Lei1, Haiping Fang1,2,3()   

  1. 1. School of Physics, East China University of Science and Technology,Shanghai 200237
    2. Wenzhou Institute, University of Chinese Academy of Sciences,Wenzhou 325001
    3. Oujiang Laboratory,Wenzhou 325000
  • Received:2022-03-08 Revised:2022-05-30 Online:2022-07-24 Published:2022-06-20
  • Contact: Haiping Fang
  • Supported by:
    National Natural Science Foundation of China(11974366); Fundamental Research Funds for the Central Universities.

溶液中的水合离子-π作用,作为一种非共价键相互作用,对研究软凝聚态物质至关重要。本文回顾了基于水合离子-π作用得到的具有反常化学计量比的二维晶体及其奇异特性,这些晶体包括常温常压条件下的氯化二钠(Na2Cl)、氯化三钠(Na3Cl)和一氯化钙(CaCl)等。这些具有反常化学计量比的二维晶体有着不同于常规三维晶体中的阴阳离子比例与独特的电子结构,具有与常规三维晶体完全不同的物理化学性质,包括室温铁磁性在内的多种特殊物理性质。这类具有反常化学计量比的铁磁性物质可能为生物体系的磁效应、磁医学的研究以及低维磁性材料的设计提供全新的思路。

关键词： 水合离子-π作用, 芳香环, 二维晶体, 反常化学计量比

Hydrated cation-π interaction, as a kind of non-covalent interaction, is essential to the study of soft condensed matter. This paper reviews the recent progress in the two-dimensional crystals of unconventional stoichiometries induced by the hydrated cation-π interaction, and their distinguished features. These crystals include Na2Cl, Na3Cl and CaCl at ambient conditions. These crystals have abnormal cation-anion ratios different from those of normal three-dimensional crystals and unique electronic structures. Consequently, their physical and chemical properties are usually different from those of normal three-dimensional crystals, including the room temperature ferromagnetism. These ferromagnetic materials of unconventional stoichiometries may provide new insight into biomagnetism, medicine-related magnetism and the design of low-dimensional ferromagnetic materials.

Contents

1 Introduction

2 Two-dimensional crystals of unconventional stoichiometries, Na2Cl and Na3Cl, at ambient conditions

2.1 Kinetic study of the enrichment and crystallization of ions in unsaturated NaCl solution on the graphene surface

2.2 Theoretical study of the crystal structure of two-dimensional Na-Cl of unconventional stoichiometries on graphene

2.3 Experimental confirmation of Na-Cl crystals of unconventional stoichiometries on rGO membranes

3 Two-dimensional crystals of unconventional stoichiometries, CaCl, at ambient conditions

3.1 Cryo-electron microscopy observations of Ca-Cl crystal structure on rGO membrane

3.2 Theoretical study of the crystal structure of two-dimensional Ca-Cl of unconventional stoichiometries on graphene

3.3 Study on the Ca-Cl crystals of unconventional stoichiometries on rGO membranes, ferromagnetism and applications of this ferromagnetic material.

3.4 Valence analysis on cations in two-dimensional crystals of unconventional stoichiometries

4 Conclusion and outlook

Key words: hydrated cation-π interaction, aromatic ring, two-dimensional crystal, unconventional stoichiometries
()
图1 苯分子和钾离子(K+)之间的阳离子-π作用模型。图中颜色从蓝到红表示分子表面静电势从正到负,球体分别代表碳原子、氢原子以及钾离子
Fig. 1 Cation-π interaction between a benzene molecule and a K+ cation. Color changing from blue to red represents the electrostatic potential changing from positive to negative, balls represent C, H atoms and the K+ cation
图2 不饱和NaCl溶液(3.0 mol/L)在石墨烯片层上的离子和水分子分布情况:(a)和(b)分别为0与40 ns时的模拟结果。青色、白色、红色的球分别代表碳、氢、氧原子,蓝色和绿色球分别代表钠和氯离子
Fig. 2 Distribution of ions and water molecules in unsaturated NaCl solution (3.0 mol/L) on the graphene sheet: (a) and (b) show the simulation snapshots at 0 and 40 ns, respectively. The cyan, white, and red balls represent carbon, hydrogen, and oxygen atoms, respectively, and the blue and green balls represent sodium and chloride ions
图3 不饱和NaCl溶液(3.0 mol/L)中Cl-离子(黑虚线)和Na+离子(黑实线)的概率密度分布,以及Na+离子的平均结合水数量(蓝线)在垂直于石墨烯表面的方向上随高度(Z)的变化曲线
Fig. 3 Probability density distribution of Cl- anions (black dashed lines) and Na+ cations (black solid lines) in unsaturated NaCl solution (3.0 mol/L), and the average hydrated water number of Na+ cations (blue lines) with the change curve of height (Z) from the graphene surface
图4 石墨烯上二维Na3Cl, Na2Cl与NaCl晶体的理论预测结构及其平均内聚能(cohesive energies)
Fig. 4 Theoretical prediction structure of two-dimensional Na3Cl, Na2Cl and NaCl crystals on graphene and their mean cohesive energies
图5 不同Na-Cl晶体结构Na-Cl间距(Distance)分布情况(Distribution)的理论计算结果。红色虚线表示常规饱和结晶形成的常规三维NaCl晶体的Na-Cl间距的峰所在位置。各曲线由上到下分别代表理论计算得到的,(1)石墨烯层间的二维Na3Cl晶体,(2)石墨烯层间的二维Na2Cl晶体,(3)石墨烯表面二维Na2Cl晶体,(4)石墨烯层间的二维NaCl晶体,(5)石墨烯表面的二维NaCl晶体,以及(6)饱和结晶的三维NaCl晶体的Na-Cl间距分布情况
Fig. 5 Theoretical calculations of Na-Cl distance distributions of different Na-Cl crystal structures. The red dotted line shows the location of the peak of the Na-Cl distance of a conventional three-dimensional regular NaCl crystal formed by conventional saturated crystals. The curves, from top to bottom, represent the calculated results of: (1) two-dimensional Na3Cl crystals between the graphene layers, (2) two-dimensional Na2Cl crystals between the graphene layers, (3) two-dimensional Na2Cl crystals on the graphene surface; (4) two-dimensional NaCl crystals between the graphene layers; (5) two-dimensional NaCl crystals on the graphene surface, and (6) Na-Cl distance distribution of the three-dimensional regular NaCl crystals of saturated crystals, respectively
图6 (a) rGO膜浸泡在不同浓度NaCl溶液所得样品的XRD衍射谱图,线上显示的NaCl溶液浓度从上到下依次为:饱和浓度4.0,3.0,2.5 mol/L;以及石墨浸泡在3.0 mol/L NaCl溶液所得样品的XRD衍射谱图。图(b)是在32°附近的局部放大图
Fig. 6 (a) XRD diffraction spectra of samples obtained by rGO membrane immersion in different concentrations of NaCl solution. The concentrations of NaCl solution shown on the line, from top to bottom, are: saturation concentrations of 4.0, 3.0, 2.5 mol/L; and XRD diffraction spectra of samples obtained by graphite immersion in 3.0 mol/L NaCl solution. (b) is a locally enlarged view near 32°
图7 rGO膜上Na-Cl晶体通过EDS测得的Na/Cl元素计量比的分布图
Fig. 7 Distribution of the Na/Cl elemental ratio for Na-Cl crystals on the rGO membrane measured by EDS
图8 rGO膜上Na-Cl晶体进行元素含量和比例的EDS测量结果,探测范围均位于红圈内,统计结果列在表格中
Fig. 8 EDS measurement results of the element content and proportion on the Na-Cl crystal on the rGO membrane. The detection area is shown in the red circle, and the statistical results are listed in the table
图9 Na-Cl@rGO膜样品的衍射斑点与Na-Cl结构拟合点的对比图。(a~d)中的彩色点分别为二维Na3Cl、二维Na2Cl、二维NaCl和常规三维NaCl晶体结构的拟合结果;图中白色点为实验结果
Fig. 9 Comparison between diffraction spots for samples of Na-Cl@rGO membranes and predicted Na-Cl structures. The colored dots in (a~d) are the fitting results of the two-dimensional Na3Cl, two-dimensional Na2Cl, two-dimensional NaCl and conventional three-dimensional regular NaCl crystal structures, respectively; the white dots in the figure are experimental results
图10 非饱和盐溶液中二维Ca-Cl晶体(a)实验流程图;(b-i) 含水的rGO膜中 CaCl晶体的冷冻电镜图像,插图是高分辨率图像放大图以及CaCl理论模型的晶体结构,其中蓝绿色和绿色小球分别表示Ca和Cl原子。(b-ii) 冷冻电镜下典型CaCl晶体的衍射斑点图,是一级衍射点在(1±0.03)/4.29 Å-1的六角衍射斑点。(b-iii) 整个明场图像的傅里叶变换结果,显示与(b-ii)中六角形衍射斑点相同。(c) Ca-Cl@rGO膜内不同深度的Ca与Cl的含量比值
Fig. 10 (a) Experimental preparation process of two-dimensional Ca-Cl crystals in unsaturated salt solution; (b-i) Cryo-EM images of CaCl crystals in rGO membranes with water; while the illustration is a high-resolution image magnification and the crystal structure of the CaCl theoretical model, where blue-green and green globules represent Ca and Cl atoms, respectively. (b-ii) Diffraction spotted pattern of typical CaCl crystals under cryo-EM, which is a hexagonal diffraction spot with a first-degree diffraction point at (1±0.03)/4.29 Å-1. (b-iii) Fourier transform results of the entire brightfield image, which show the same as the hexagonal diffraction spot in (b-ii). (c) Content ratio of Ca to Cl at different depths within the Ca-Cl@rGO membranes
图11 理论计算得到的石墨烯上5个相对最稳定的二维CaCl@graphene结构及相应的内聚能
Fig. 11 Five stable two-dimensional structures of CaCl@graphene, and the corresponding cohesion energies by theoretical calculation
图12 rGO膜和Ca-Cl@rGO膜的干样品(a),以及Cu-Cl@rGO膜的干样品(b)的磁矩M与外加磁场H的关系图,磁场垂直于样品表面。插图是各样品剩磁和矫顽力测量结果的放大图
Fig. 12 Hysteresis loop images for dry samples of rGO membranes and Ca-ClrGO membranes (a), and dry samples of Cu-ClrGO membranes (b). The magnetic field is perpendicular to the sample surface. The illustration is a magnification of the measurements of residual magnetism and coercivity in each sample
图13 ICP-OES对Ca-Cl@rGO膜样品以及纯rGO膜样品的测试结果
Fig. 13 ICP-OES results for samples of Ca-Cl@rGO membrane, and rGO membrane samples
图14 相同石墨烯基底上根据CaCl@graphene结构1所构建的含有不同个数(N)的(CaCl)N晶体簇构型图,N为1~8的整数
Fig. 14 Crystal cluster configurations of (CaCl)N on the same graphene substrate with different number (N), based on the structure 1
表1 (CaCl)N晶体簇具有的磁矩以及每个CaCl平均磁矩
Table 1 Magnetic moment for (CaCl)N crystal clusters and the mean magnetic moment for each CaCl unit, respectively
CaCl (CaCl)2 (CaCl)3 (CaCl)4 (CaCl)5 (CaCl)6 (CaCl)7 (CaCl)8
Total moment
M (μB)		 0.7677 1.4706 0.4659 1.4136 0.8665 0.9768 1.5687 1.3728
M/N (μB) 0.7677 0.7353 0.1553 0.3534 0.1733 0.1628 0.2241 0.1716
图15 含Ca-Cl的Ca-Cl@GO和Ca-Cl@rGO膜样品与相应对照组的电阻率比较
Fig. 15 Electrical resistivities of samples: Ca-Cl@GO membranes and Ca-Cl@rGO membranes, and the corresponding control groups
图16 不同厚度的石墨烯(Graphene)片层和对应厚度的Ca-Cl@graphene样品的电阻对比图
Fig. 16 Resistance comparison of graphene sheets with different thicknesses and Ca-Cl@graphene samples with corresponding thicknesses
图17 理论模型的电子结构图。(a) CaCl@graphene结构1中无石墨烯基底二维Ca-Cl晶体的元素能带投影和电子态密度图;(b) 完整CaCl@graphene结构1模型中元素能带投影和电子态密度图;图(a)和(b)中点的大小表示该元素的贡献权重,插图表示在布里渊区高对称q点的路经。EF表示费米能级
Fig. 17 Electronic structures of the theoretical models. Element energy bands and electron state density diagram of (a) two-dimensional Ca-Cl crystals without graphene; (b) complete CaCl@graphene model (Structure 1). The size of the dots in figures (a) and (b) represents the contribution weights of the element. The illustration shows the path of the highly symmetrical q-spot in Brillouin. EF stands for Fermi energy level
图18 理论计算三种结构在费米能级附近的电子态密度图:无石墨烯基底的二维Ca-Cl晶体模型(CaCl alone)、单层石墨烯模型(Graphene)、CaCl@graphene结构1 (Structure 1),分别用蓝色、黑色和红色表示
Fig. 18 Electron state density images of the three structures near the Fermi energy level: a two-dimensional Ca-Cl crystal model (CaCl alone) without graphene substrate, a single-layer graphene model (Graphene), and CaCl@graphene model (Structure 1), represented by blue, black, and red, respectively
图19 Ca-Cl@rGO膜的干样品类压电特性:在弯曲角随时间的变化,且最大角度是90°条件下,Ca-Cl@rGO膜的干样品和rGO膜在周期性应变下的典型电压响应
Fig. 19 Piezoelectric characteristics of Ca-ClrGO membrane: typical voltage response of dry Ca-Cl@rGO membrane and rGO membrane samples, under periodic strain under periodic strain, and with the condition that the bending angle changes with time and the maximum angle is 90°
图20 Ca-Cl@rGO膜(红色)和rGO膜(蓝色)的电流-电压曲线。插图是两个铜箔电极连接rGO膜测试电流-电压曲线示意图
Fig. 20 Current-voltage curve of Ca-ClrGO membrane (red) and rGO membrane (blue). The illustration is a schematic diagram of two copper foil electrodes connected to the rGO membrane, to measure the current-voltage curve
图21 金属Ca、Ca-Cl@rGO膜干样品和正常的CaCl2各两处样品区域的X射线近边吸收精细结构谱,分别用蓝色、红色、黑色实线表示
Fig. 21 Calcium near-edge X-ray absorption fine structure spectra (NEXAFS) of two sampling areas of the regular calcium metal, the regular CaCl2 crystals and the Ca-Cl crystals in rGO membrane are represented by blue, red, and black solid lines, respectively
图22 Cu L3和L2边缘的三种Cu-Cl化合物的NEXAFS光谱结果图。黑色线:rGO膜;蓝色线:常规三维CuCl2晶体样品;红色线:Ca-Cl@rGO膜干样品;栗色线:常规三维CuCl晶体样品
Fig. 22 NEXAFS spectra of four Cu-Cl compounds at the Cu L3, 2 edges. Black: the rGO membrane; blue: regular CuCl2 crystals; red: the Cu-Cl crystals in the dried Ca-Cl@rGO membrane; maroon: regular CuCl crystals
图23 rGO膜上的Cu-Cl晶体的XPS结果图。红色和绿色线分别表示制备好后存放了10天和3天的Cu-Cl@rGO膜干样品的测量结果。栗色线表示常规三维CuCl晶体样品的测量结果;蓝色线表示常规三维CuCl2晶体样品的测量结果
Fig. 23 X-ray photoelectron spectroscopy (XPS) of Cu-Cl crystals in the dried rGO membranes. Red and green: the dried rGO membranes with Cu-Cl crystals had been prepared for 10 days and 3 days, respectively. Maroon: CuCl crystals; blue: regular CuCl2 crystals
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