Poly(styrene sulfonate) layered double hydroxide nanocomposites. Stability and subsequent structural transformation with changes in temperature

Poly(styrene sulfonate)–Zn2Al(OH)6·nH2O (PSS–LDH) layered double hydroxide nanocomposites have been prepared by the polymer templating method or by an exchange reaction followed by in situ polymerization of the monomers. The two well-defined samples were characterized by a combination of techniques and the polymerization of styrene sulfonate evidenced by 13C CP-MAS experiments. The nanocomposites were further characterized by in situ XRD measurements at different temperatures. The basal spacing differs in the two samples; it is stable up to 450 °C for the material synthesized by the polymer templating method, whereas a large contraction is observed for the other sample. Grafting reactions were not observed during thermal treatment. The pristine chlorine LDH material first underwent a contraction attributed to the loss of intracrystalline water molecules followed by an expansion before the breakdown of the lamellar framework at 200 °C. The microstructural transformations and the nature of the by-products are independent of the atmosphere. In contrast, drastic changes occur in the nanocomposites. A ZnS-like phase is evidenced by EDX analysis and an EXAFS study at the sulfur K-edge after treatment at 600 °C under a nitrogen atmosphere; ZnS was observed to crystallize at higher temperatures. For the templating assisted nanocomposite, an intermediate phase Zn3O(SO4)2 was observed in air. The organic moiety is found to delay the crystallization of the metal oxides, ZnO (zincite) and ZnAl2O4 (gahnite); treatment under N2 atmosphere also shows this trend.