Delamination and restacking of a layered double hydroxide with nitrate as counter anion

Abstract

A layered double hydroxide (LDH) with nitrate as the counter anion (LDH–NO₃ with Mg/Al = 3) was, for the first time, successfully delaminated in formamide under ultrasonic treatment. Atomic force microscopy (AFM) images showed that a large part of the LDH was delaminated into single and double brucite layers (0.7–1.4 nm in thickness). The nano-sheets had disk-like shapes with a diameter of ca. 20–40 nm. Findings from AFM were in good agreement with the average hydrodynamic diameter determined using dynamic light scattering. Powder X-ray diffraction pattern of LDH dispersed in formamide also confirmed that LDH–NO₃ was exfoliated. The dispersions of LDH in formamide were stable and transparent up to a concentration of 40 g L⁻¹. However, formation of transparent gels was observed at concentrations higher than 5 g L⁻¹. Delaminated LDH could be restacked by adding sodium carbonate or ethanol.