Growth of Layered Double Hydroxide on a Micrometer-Sized Glass Porous Solid

Particle growth within micrometer-sized porous solids was revealed through nondestructive synchrotron radiation (SR) analysis. In this study, the precipitation of platy particles of layered double hydroxide (LDH) was conducted in the presence of glass porous solids containing interconnected pores formed by fusion of glass beads at the onset of sintering. During the hydrothermal reaction of magnesium–aluminum-type LDH (MgAl-LDH) in the presence of the disk-shaped glass porous solids, the disk shape was preserved while white precipitates formed. Vertically aligned platy particles first precipitated at the necks between glass beads and subsequently covered the glass-bead surfaces from the exterior toward the interior regions, as revealed by complementary analyses including X-ray diffraction, scanning electron microscopy, elemental analyses, and SR multiscale X-ray computed tomography. The SR analysis, a nondestructive technique, successfully visualized LDH platy layers covering the interior surfaces of the porous solid without manual or mechanical processing to obtain disk cross sections, which could otherwise damage the layers. These analyses also revealed that MgCO3 particles precipitated through the rapid consumption of Al3+ (Mg/Al molar ratio of the starting solution = 4) during or after LDH formation. This behavior is supported by the growth of smaller LDH particles vertically aligned on larger ones on both the glass surfaces and the resulting powders, consistent with the general interpretation of the preferential incorporation of Al3+ into LDH layers compared with Mg2+. Notably, such particles were not generated without the addition of the glass porous solid. Therefore, the results in this study elucidate the precipitation mechanisms of LDH platy particles in bulk porous solids with micrometer-sized interconnected pores, which show potential for treatment of large amounts of water treatment. Thus, this study paves the way for preparing easily handled and bulk inorganic materials composed of naturally abundant elements with increased surface area.