Preparation Of LDH/MMT Nanocomposite Based On The Exfoliation And Assembly Behavior Of Montmorillonite

In this paper, sodium-montmorillonite(NaMt) and organic montmorillonite(OMt) were obtained by sodium modification and organic modification of Inner Mongolia calcium-montmorillonite(CaMt). Exfoliation behaviors of CaMt, NaMt and OMt were studied by mechanical ball grinding and ultrasoniction. LDH/MMT nanocomposite was prepared by in situ growth of LDH grown on the disordered platelets of montmorillonite which played as templates. The exfoliation and assembly behavior of montmorillonite and the LDH/MMT nanocomposite were studied by X-ray diffraction(XRD), scanning electron microscopy(SEM), transmission electron microscopy(TEM), atomic force microscope(AFM), FTIR spectrum and so on. The main work and conclusions are drawn as follows:Exfoliated montmorillonite was obtained by mechanical ball grinding and ultrasoniction. The exfoliation and assembly behavior of montmorillonite was studied by using mechanical ball grinding and ultrasonication of CaMt, NaMt and OMt in ethanol solvent, respectively. The exfoliation and assembly of montmorillonite is a reversible process. Compared with the exfoliation effect of CaMt and OMt, exfoliation of NaMt can be easier. The diameter and the thickness of NaMt platelets decreased greatly. The average thickness of NaMt platelets is about 15 nm; the interlayer organic matters of OMt may be a resistant when the montmorillonite platelets were treated by mechanical ball grinding, which had a stable effect on montmorillonite platelets. It revealed that Organic modification of montmorillonite can not promote the exfoliation effect by the mechanical ball grinding.LDH/MMT nanocomposite was prepared through hydrothermal method by using the raw materials of magnesium nitrate, aluminum nitrate and ammonia solution.The LDH/MMT composite of Mt and LDH platelets were assembled with montmorillonite platelets in composite exfoliated structure. The in situ grown LDH crystals, as spacer, played a crucial role of preventing the restacking of the disordered Mt platelets. It can be inferred that the force of continuous nucleation and in situ growth of LDH caused the exfoliation of montmorillonite platelets.Influences of Mg: Al molar ratio, ultrasonication and the initial pH of the hydrothermal system on the structure of LDH/MMT nanocomposite were studied. The obtained results showed that the structure of LDH/MMT nanocomposite changed when the Mg: Al molar ratio increased in the dispersion. There were two kinds of formation of LDH in LDH/MMT nanocomposite when the Mg: Al mole ratio of 1:1 and 2:1. Some of them assembled with montmorillonite platelets and the other part was independent LDH. The change of PH had an effect on the crystallinity of LDH in LDH/MMT nanocomposite. With the increase of pH, the crystallinity of LDH in LDH/MMT nanocomposite decreased. Ultrasonication can accelerate the exchange of metallic cations and promote the distribution surrounding montmorillonite platelets as Mg(NO3)2·6H2O and Al(NO3)3·9H2O were added in the dispersion system. This guarantied the nucleation and in situ growth of LDH crystallites took place on the disordered Mt platelets and avoided the impurity phase of AlO(OH). In the preparation of montmorillonite dispersions, increase of the content of montmorillonite in dispersions can promote the content of montmorillonite in LDH/MMT nanocomposite. The montmorillonite platelets in LDH/MMT nanocomposite was still exfoliated when the content of montmorillonite in dispersions was 0.017 g/mL. The less content of montmorillonite platelets included in LDH/MMT nanocomposite, the thinner exfoliated montmorillonite platelets were obtained.