Critical role of water structure around interlayer ions for ion storage in layered double hydroxides

Abstract

Water-containing layered materials have found various applications such as water purification and energy storage. The highly structured water molecules around ions under the confinement between the layers determine the ion storage ability. Yet, the relationship between the configuration of interlayer ions and water structure in high ion storage layered materials is elusive. Herein, using layered double hydroxides, we demonstrate that the water structure is sensitive to the filling density of ions in the interlayer space and governs the ion storage. For ion storage of dilute nitrate ions, a 24% decrease in the filling density increases the nitrate storage capacity by 300%. Quartz crystal microbalance with dissipation monitoring studies, combined with multimodal ex situ experiments and theoretical calculations, reveal that the decreasing filling density effectively facilitates the 2D hydrogen-bond networking structure in water around interlayer nitrate ions along with minimal change in the layered structure, leading to the high storage capacity.

Molecular-Level Pictures of Chemical and Structural Transformations of Mg–Al Layered Double Hydroxide Crystals (Mg/Al = 2) at Elevated Temperatures

“…Layered double hydroxides (LDHs) are layered compounds that have been known for a long time but have recently been attracting much attention owing to their wide variety of advanced functions. Layered nickel hydroxides and Fe-containing LDHs are promising as electrode catalysts for water oxidation. , Solid base catalysis for organic chemical reactions, − photocatalysis for CO 2 reduction, , and ion storage materials are also important research fields for green chemistry and sustainable energies. Recently, developed techniques have enabled the synthesis of LDH nanomaterials, such as nanocrystals − and nanosheets .…”

Layer-Stacking Sequence Governs Ion-Storage in Layered Double Hydroxides

“…In brief, high nitrate ion intercalation in the dilute regime is driven by enhanced interlayer binding forces, while the capacity that remains at a low level in concentrated regime is due to weakened interlayer binding forces owing to further nitrate ion inclusion into the interlayer spaces. Remarkably, our previous study suggested that this transformation in the interlayer environment of the LDHs structure includes a 2D to 3D transformation of the hydrogen-bonding network between the interlayer ions and water molecules …”

“…QCM-D is an effective in situ measurement tool for understanding the ion dynamics in matter. From the change in the frequency (Δ f ) value, the real-time mass transfer of inter­(de)­intercalating ion in association with water can be monitored. − Importantly, dissipation (Δ D ) monitoring has been long utilized for studying the dynamic deformation behaviors accompanying viscoelastic change in water-containing soft matter. , The viscoelasticity of the LDHs represents the overall interlayer binding force . Therefore, by simultaneously monitoring the Δ D values and Δ f , the dynamic change in the interlayer binding force along with mass transfer of LDHs upon nitrate intercalation is studied (Figure b).…”

“…32,33 The viscoelasticity of the LDHs represents the overall interlayer binding force. 34 Therefore, by simultaneously monitoring the ΔD values and Δf, the dynamic change in the interlayer binding force along with mass transfer of LDHs upon nitrate intercalation is studied (Figure 3b). For this, the as-prepared LDHs were deposited on SiO 2 -coated Au electrodes (Figure S3) and examined by QCM-D. Wherein, at first, a concentrated aqueous 200 mM NaCl aqueous solution was flown and subsequently an aqueous 200 mM NaNO 3 solution was flown by changing flow channel (Figure 3b).…”

“…Remarkably, our previous study suggested that this transformation in the interlayer environment of the LDHs structure includes a 2D to 3D transformation of the hydrogen-bonding network between the interlayer ions and water molecules. 34 LDHs-R with the 3R 1 polytype exhibited an induction period in the early nitrate ion storage regime (Figure 3c), during which there was an apparent absence of variations in both the dissipation and the frequency. After the induction period, a gradual decrease in dissipation and an increase in frequency were observed.…”