Characterization of exfoliated layered double hydroxide (LDH, Mg/Al=3) nanosheets at high concentrations in formamide

For the first time procedures for the direct characterization of exfoliated nanosheets of LDH (Mg/Al = 3) in suspension are reported. The shape, size and layer thickness of the nanosheets were determined using small angle X-ray and neutron scattering (SAXS/SANS) in combination with dynamic light scattering (DLS) and atomic force microscopy (AFM). Furthermore, by using ultrasonic treatment we were able to delaminate a glycinate containing LDH up to a concentration of 42.5 g L-1, which is ten times higher than the value reported in the literature for the same system. The exfoliated LDH nanosheets were directly characterized in suspension by SAXS/SANS and gave an average layer thickness of 1.4 nm for both tested concentrations ( 10 and 42.5 g L-1). This result provides strong evidence that the LDH, even at concentrations as high as 42.5 g L-1, is totally delaminated into single or a few stacked brucite layers. AFM images of exfoliated LDH, after dilution and deposition on mica, confirm that exfoliated nanosheets mainly consist of single and double layers, corresponding to thicknesses of 0.6 +/- 0.1 and 1.3 +/- 0.1 nm, respectively. The diameters of the nanosheets in suspension determined using SAXS and SANS are very similar ( between 30 and 40 nm), and are in good accordance with the value observed by AFM ( between 10 and 40 nm). Hydrodynamic diameters determined by dynamic light scattering ( DLS) were 35 and 60 nm at 10 and 42.5 g L-1, respectively.