Investigating Local Structure in Layered Double Hydroxides with ¹⁷O NMR Spectroscopy

Probing Local Structure of Layered Double Hydroxides with 1H Solid-State NMR Spectroscopy on Deuterated Samples

“…28 The separation between Mg 2 AlOH and Mg 3 OH is still significant, and the three different signals can be distinguished, which allows the quantification of the different H sites (H 2 O, Mg 2 AlOH, and Mg 3 OH) and the cation arrangement information extraction ( Figure 2a). 14,16,17 The mole percentages of Mg 2 AlOH and Mg 3 OH species in the NO 3 − -containing LDHs extracted in this study agree well with the predictions made assuming Al−O−Al linkage avoidance, which is also consistent with the results from previous NMR investigations (Figure 2b). 14,16,17 No MgAl 2 OH site was observed at a high Al mole percentage of 32.3%, which is different from the results obtained by Cadars and co-workers; again, we believe that different preparation methods lead to their observation of the Al−O−Al defects.…”

“…14,16,17 The mole percentages of Mg 2 AlOH and Mg 3 OH species in the NO 3 − -containing LDHs extracted in this study agree well with the predictions made assuming Al−O−Al linkage avoidance, which is also consistent with the results from previous NMR investigations (Figure 2b). 14,16,17 No MgAl 2 OH site was observed at a high Al mole percentage of 32.3%, which is different from the results obtained by Cadars and co-workers; again, we believe that different preparation methods lead to their observation of the Al−O−Al defects. 15 The much improved resolution among the three different H species proves that deuterium has been successfully introduced to Mg 3 OH, Mg 2 AlOH, as well as interlayer H 2 O during deuteration.…”

Local environment and composition of magnesium gallium layered double hydroxides determined from solid-state 1H and 71Ga NMR spectroscopy

“…Figure 4 shows the 71 Ga MAS NMR spectra of three MgGa LDH's, which are very similar and display the distinct quadrupolar broadened line shape for a Ga site with a fairly large quadrupole interaction. Line shape analysis show that the experimental spectra can be simulated by a single 71 Ga site (Figure 4), characterized by CQ = 5.35 (10), Q = 0.05 (10), and iso( 71 Ga) = 40(2) ppm.…”

“…Thus, the ordering of M(III) and M(II)/M(III) ratios can be determined if the -OH groups can be quantified. It has been demonstrated that solid-state NMR (SSNMR) provides this information and gave a detailed insight into local environment of the cation in magnesium aluminum (MgAl) LDH's [6][7][8][9][10][11], including the distribution of Al in the cation layer, the presence of structural defects -information which is very difficult determined with X-ray diffraction techniques, which rely on long range order. The dynamics and orientation of both inorganic and organic anions in the interlayer has been extensively studied by Kirkpatrick et al [12][13][14][15][16][17][18].…”

“…SSNMR studies have found MgAl LDH's to be ordered, but they may contain structural defects on the atomic level [7][8][9][10][11]. There are contradicting observations as to whether the structure contains Al-O-Al connectivities or not, which has been ascribed to different methods of [7].…”