Effect of the Mg:Al Ratio on Borate (or Silicate)/Nitrate Exchange in Hydrotalcite

Layered double hydroxides (LDHs) have been prepared with interlayer nitrate and with different Mg:Al ratios. Solids with low Mg:Al ratios show larger basal spacings than those with larger Mg:Al ratios, consistent with tilting of the nitrate ions, respectively. Nitrate/tetraborate and nitrate/silicate anionic exchange has been achieved only for those samples with "tilted" nitrate. The precise nature of the interlayer species in the exchanged samples has been concluded from MAS–NMR results. The layered structure of the exchanged samples collapses at temperatures higher than those for the nitrate-containing precursors.