Control of Micro- and Nanostructures of Layered Double Hydroxides by Hydrothermal Treatment

Abstract

Layered double hydroxides (LDHs) are mixed M(II) and M(III) hydroxides with positively charged lamellar brucite layers and interlayered anions. LDHs have attracted significant attention due to their anion- and cation-exchange ability, adsorption capacity, and potential applications in drug delivery and catalysis. The properties of LDHs directly correlate with their structures. In this study, we synthesized nickel-aluminum LDHs by the sol–gel method. We investigated the changes in their crystal structure/morphology introduced by hydrothermal treatments that varied from 0 to 48 h. Based on measured data using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and synchrotron-based small-angle X-ray scattering, we demonstrated that the duration of the hydrothermal treatment can effectively control the micro- and nanostructures of Ni–Al LDHs. We found that the hydrothermal treatment leads to a two-step change in the structure of the LDHs. In the first step, crystallization occurred during the first 24 h of hydrothermal treatment, increasing the interlayer width (from 2.28 to 2.31 nm) and the crystallite size (from 14.2 to 50.6 nm). In the second step, the predominant phenomena were stacking and planar expansion after the crystallization process approached equilibrium. Thus, the layered structure already developed in the first step was further stacked, and the hexagonal platelet characteristic of LDH expanded in a planar direction. Our study suggests that the duration of the hydrothermal treatment is a crucial factor in the structural evolution of LDHs and can be used to control the structure of LDHs for different applications.

Enhancing Catalytic Performance with Sol‐Gel Hydrotalcite‐Derived Nickel Oxide Catalysts for Dry Reforming of Methane: An Examination on Reactivity and Coke Formation

“…[12][13][14] The reactivity of metal salts precursors can be controlled using sol-gel chemistry, which involves a branched alkoxide and metal cation size. [15][16] Sol-gel synthesis provides precise control over surface and textural properties, resulting in materials with large specific areas and uniform pore distribution. [16] Hydrotalcites can incorporate a transition metal via ion exchange while preserving inorganic and organic anions.…”

“…Sol‐Gel synthesis is a good method for preparing hydrotalcites and oxides with improved textural and morphological properties and low crystallinity [12–14] . The reactivity of metal salts precursors can be controlled using sol‐gel chemistry, which involves a branched alkoxide and metal cation size [15–16] . Sol‐gel synthesis provides precise control over surface and textural properties, resulting in materials with large specific areas and uniform pore distribution [16] .…”