Inter layer interaction in Ca-Fe layered double hydroxides intercalated with nitrate and chloride species

International audienceCa-Fe layered double hydroxide (LDH) intercalated with chloride and nitrate ions has been synthesized with varying Ca-II:Fe-III molar ratios of the initial solution. Phase pure LDH is observed with Ca-II:Fe-III molar ratio of 2:1 and a mixture of LDH and Ca(OH)(2) is formed for Ca-II:Fe-III molar ratios higher than 2:1. Vibrational spectroscopies (Raman and IR) were used successfully to understand the interaction between the cationic and anionic sheets. The Raman bands positions at lower frequencies (150-600 cm(-1)) are intimately correlated to the nature of the divalent and trivalent ions but also to the nature of the anions. Indeed, a shift of similar to 9 cm(-1) is observed for the Raman double bands situated in the 300-400 cm(-1) region when comparing Raman spectra of CaFe-LDH containing either nitrate or chloride ions. Two types of nitrate environments are observed namely free (non-hydrogen bonded) nitrate and nitrate hydrogen bonded to the interlayer water or to the `brucite-like' hydroxyl surface. Multiple types of water structure are observed and would result from different hydrogen bond structures. Water bending modes are identified at 1645 cm(-1) greater than the one observed for LDH intercalated with chloride anions (1618 cm(-1)), indicating that the water is strongly hydrogen bonded to the nitrate anions