Regulation of Structure and Anion-Exchange Performance of Layered Double Hydroxide: Function of the Metal Cation Composition of a Brucite-like Layer

Abstract

As anion-exchange materials, layered double hydroxides (LDHs) have attracted increasing attention in the fields of selective adsorption and separation, controlled drug release, and environmental remediation. The metal cation composition of the laminate is the essential factor that determines the anion-exchange performance of LDHs. Herein, we review the regulating effects of the metal cation composition on the anion-exchange properties and LDH structure. Specifically, the internal factors affecting the anion-exchange performance of LDHs were analyzed and summarized. These include the intercalation driving force, interlayer domain environment, and LDH morphology, which significantly affect the anion selectivity, anion-exchange capacity, and anion arrangement. By changing the species, valence state, size, and mole ratio of the metal cations, the structural characteristics, charge density, and interlayer spacing of LDHs can be adjusted, which affect the anion-exchange performance of LDHs. The present challenges and future prospects of LDHs are also discussed. To the best of our knowledge, this is the first review to summarize the essential relationship between the metal ion composition and anion-exchange performance of laminates, providing important insights for regulating the anion-exchange performance of LDHs.

Keywords: anion-exchange performance; intercalation driving force; interlayer domain; layered double hydroxide; metal cation composition; structure regulation.

Figure 6

(a) Schematic illustration of the proposed “ion-exchange and expansion-extrusion” mechanism for MO on Co₄Al₁−Cl LDH. Reproduced with permission from [28]. Plots of the released concentrations of (b) SeO₄²⁻ and (c) Mg²⁺ ions after the reaction. (d) X-ray diffraction (XRD) patterns of the pristine Mg₂Al−LDH and solid residues after the sorption reaction. Reproduced with permission from [45].

Figure 1

(a) Color-filled electron localization function diagram. (b) Optimized structure and independent gradient model based on a Hirshfeld partition (IGMH) map (isovalue = 0.01 a.u.). (c) Sign(λ₂)ρ—colored IGMH scatter plot. (d) Colored atoms based on their contribution to the interaction energy. (e) Electrostatic potential mapping on the van der Waals surface. (f) Isosurface map of the van der Waals potential using C as the probe atom. Reproduced with permission from [14].

Figure 2

(a) Mechanism of the substitution of CO₃²⁻ anions by methyl orange (MO); (b) snapshot of the interactions between the MO/CO₃²⁻ and layered double hydroxide (LDH) layers and (c,d) π–π stacking of MO in an LDH simulated by the Monte Carlo method. Reproduced with permission from [17].

Figure 3

(a) Zeta potentials of Zn–Al and Mg–Al LDHs at pH 3–11; (b) adsorption kinetics of perfluorooctanoic acid (PFOA) onto the Zn–Al and Mg–Al LDHs at pH 6 with an initial PFOA concentration of 10 mg/L and adsorbent loading of 0.25 g/L. The dashed lines represent pseudo-second order model fits. (c) Adsorption isotherms of PFOA onto the Zn–Al and Mg–Al LDHs at pH 6 with an adsorbent loading of 0.25 g/L; (d) effect of the ionic strength on PFOA adsorption onto the Zn–Al and Mg–Al LDHs. Reproduced with permission from [26].

Figure 3

(a) Zeta potentials of Zn–Al and Mg–Al LDHs at pH 3–11; (b) adsorption kinetics of perfluorooctanoic acid (PFOA) onto the Zn–Al and Mg–Al LDHs at pH 6 with an initial PFOA concentration of 10 mg/L and adsorbent loading of 0.25 g/L. The dashed lines represent pseudo-second order model fits. (c) Adsorption isotherms of PFOA onto the Zn–Al and Mg–Al LDHs at pH 6 with an adsorbent loading of 0.25 g/L; (d) effect of the ionic strength on PFOA adsorption onto the Zn–Al and Mg–Al LDHs. Reproduced with permission from [26].

Figure 4

Crystal structure and schematic image of the fluorine substitution of a brucite-like layer of LDHs, visualized using the Visualization for Electronic Structural Analysis program, and molecular structures of the target ion in this study. Reproduced with permission from [33]. Copyright {2020} American Chemical Society.

Figure 5

(a) Schematic of the binding force transformation between Cr(VI) and hydrocalumite with different Cr(VI) loadings. (b) Plot for the k_d values versus Cr/Cl ratios. Reproduced with permission from [40]. Copyright {2021} American Chemical Society. (c) Proposed As(V) removal mechanism by calcined Mg–Al–Fe LDH. Reproduced with permission from [41].

Figure 7

(a) Schematic illustration of the synthesis of Fe²⁺−NiFe LDH; (b) zeta potential of Ni−Fe LDH and Fe²⁺−NiFe LDH as a function of pH; (c) effect of the initial pH on Cr(VI) removal by Ni−Fe LDH and Fe²⁺−NiFe LDH; (d) Cr 2p spectrum of Fe²⁺−NiFe LDH after Cr(VI) adsorption. Reproduced with permission from [57].

Figure 8

(a) XRD pattern of (003) reflexes for various MgMAl LDHs. (b) Relationship between the atomic radius, d-spacing, and grain size of the MgAl−LDHs substituted with 5% divalent transition metals. Reproduced with permission from [59]. (c) High resolution transmission electron microscopy (TEM) image of LaLiAl LDH. (d) Selected area electron diffraction pattern of LaLiAl LDH. Reproduced with permission from [60].

Figure 9

(a) Schematic illustration of the synthesis of graphene oxide (GO)−Ni−Fe LDH. (b) Absorption capacities of the Ni−Fe LDH and GO−NiFe LDH composite. Reproduced with permission from [65]. (c) Synthesis procedure for the LDH@biomass-derived porous carbon (PAB) composite. (d) TEM image of the LDH@PAB composite. Reproduced with permission from [66]. (e) Synthesis process of the MgNiCo LDH hollow structure (MNC HS), and its (f) field emission scanning electron microscopy (FESEM) and (g) TEM images. (h) Kinetic curves for Congo red (CR) adsorption on the MNC and MNC HS samples (CR concentration = 50 mg L⁻¹, adsorbent dose = 0.1 g L⁻¹, T = 30 °C). Reproduced with permission from [67].

Figure 10

(a) Schematic of the fabrication and modification of NiFe LDH-Top@Cl. Scanning electron microscopy images of (b) NiFe LDH-Top (10 µm), (c) NiFe LDH-Top@Cl (10 µm), and (d) NiFe LDH-Top@Cl (5 µm). Reproduced with permission from [77]. Copyright {2021} American Chemical Society.

Figure 11

Schematic of the synthesis of hollow Ni–Fe–Ce LDH microcapsules. Reproduced with permission from [84].

Figure 12

(a) XRD patterns; (b) selected XRD pattern insets of the (003) diffraction peak; and (c–f) corresponding FESEM images for CoAl−LDH, CoZnAl−LDH−5.5:0.5:2, CoZnAl−LDH−5:1:2, and CoZnAl−LDH−4:2:2, respectively. Reproduced with permission from [85].

Figure 13

Schematic for the synthetic procedure and adsorption mechanisms of organic Zn–Cr LDH, named ST−LDH, for MO, using a one-step hydrothermal method and MO as a soft template. Reproduced with permission from [118].

Figure 14

Schematic plot of the preparation, accumulation at the tumor site, and internalization into the cancer cells of hyaluronic acid/polyethylene glycol-graft-polyglutamic acid@LDHs@ diethyldithiocarbamate/doxorubicin. Reproduced with permission from [137].