A layered double hydroxide (LDH) with nitrate as the counter anion (LDH-NO 3 with Mg/Al = 3) was, for the first time, successfully delaminated in formamide under ultrasonic treatment. Atomic force microscopy (AFM) images showed that a large part of the LDH was delaminated into single and double brucite layers (0.7-1.4 nm in thickness). The nano-sheets had disk-like shapes with a diameter of ca. 20-40 nm. Findings from AFM were in good agreement with the average hydrodynamic diameter determined using dynamic light scattering. Powder X-ray diffraction pattern of LDH dispersed in formamide also confirmed that LDH-NO 3 was exfoliated. The dispersions of LDH in formamide were stable and transparent up to a concentration of 40 g L 21 . However, formation of transparent gels was observed at concentrations higher than 5 g L 21 . Delaminated LDH could be restacked by adding sodium carbonate or ethanol.

SAPO-34 (SAPO:  silicoaluminophosphate) has been synthesized and examined by in situ multinuclear high-resolution NMR under hydrothermal conditions (170 °C) in the presence of HF, using morpholine as the structure-directing agent. Four routes have been examined:  (a) from a SAPO gel with HF (triclinic SAPO-34), (b) from a SAPO gel without HF (trigonal SAPO-34), (c) from an AlPO4 gel with HF (triclinic AlPO4-34), and (d) from a slurry containing the layered AlPO4F prephase (triclinic AlPO4-34). In situ 13C, 19F, 27Al, and 31P NMR have uncovered the main steps of the reaction. The gel dissolves into small units condensed to no more than 4-rings (4R). The next steps are formation of a layered intermediate (the prephase), redissolution of the prephase into 4R building units of different types depending on the fluoride contents and aluminum coordination, and the subsequent nucleation and crystallization of triclinic AlPO4/SAPO-34. The initial fast process leads to the formation of the prephase made of an alternating stacking of 4R type-II units. When approaching 170 °C, this phase redissolves in 4R type-III units with aluminum in five-coordination. With additional defluorination, 4R type-IV units transform into 4R type-V units and both types connect in a chabazite topology. One 4R type-IV unit clips two fluorine atoms into the bridging position in the 4-ring and subsequently shapes the network topology into its crystalline order. The mechanism provided can now be subjected to further chemical testing for purposes of syntheses optimization.

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The kinetics of formation of SAPO-34 in the presence of HF and with morpholine as a structure-directing agent has been monitored by in situ X-ray powder diffraction. Examination of the gel as a function of various heating profiles and final synthesis temperatures demonstrates the importance of the heating history. At lower temperatures, a layered "prephase" has been obtained with general empirical formula resembling [AlPO 4 F] × 0.87 C 4 H 9 ON-H. On indexing powder X-ray diffraction data, a monoclinic unit cell with dimensions a ) 14.473 Å, b ) 6.930 Å, c ) 9.239 Å, and β ) 101.54°was found with high figures of merit. An additional disordered phase, most probably a layered structure, appears as a transient phase during transformation of the prephase to SAPO-34. It has been shown that these two precursors are of major importance for obtaining SAPO-34 under the conditions studied. In addition, use of the prephase as starting material with the addition of water produces triclinic AlPO 4 -34 (Si free) after hydrothermal treatment at 180 °C for 24 h. The kinetics of formation have been examined in the presence of hydrofluoric acid as a function of the final synthesis temperature using a two-step heating profile. The crystallization curves were fitted to the Avrami-Erofeyev equation, and activation energy of 158 kJ/mol for the formation of triclinic SAPO-34 was determined from an Arrhenius plot.

Gels prepared for the synthesis of SAPO-34, with morpholine as a structure-directing agent, have been characterized by multinuclear (1H, 13C, 19F, 27Al, and 31P), high-resolution NMR at room temperature. Less complex solutions are prepared and analyzed to aid in the peak assignment. Although some spectral features remain unresolved, the overall analysis is qualitatively consistent with the expected complex chemistry taking place in these solutions. Systems in the presence and absence of HF reveal significant spectral differences. It has been shown that pH can be monitored by the proton and carbon chemical shift of morpholine. In addition, 1H and 13C NMR spectra suggest that the structure-directing agent is an inactive species at room temperature independent of the presence or absence of HF. This is contrary to the 27Al NMR, where it has been concluded that morpholine has a significant influence on the aluminum coordination, giving tetrahedral Al when HF is absent. The existence of octahedral aluminophosphate−fluoride complexes is evident in the presence of HF, while several octahedral aluminophosphate complexes are formed in the absence of HF and morpholine. No sign of interactions between aluminum and silicon, silicon and phosphates, silicon and morpholine, phosphates and morpholine, or morpholine and fluoride has been observed within the concentration range studied. Some time-resolved studies have revealed that the aging is shown to influence the type and the amount of species present in the solutions.

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The pH has been measured in situ by 13C NMR during hydrothermal formation of SAPO-34 (SAPO:  silicoaluminophosphate) in the presence of hydrofluoric acid and with morpholine as the structure-directing agent. Morpholine, with a pKa of about 8.8 at room temperature, can be used as a pH probe within the region 7.3 < pH < 10.3. The pH was determined to be 5.5 immediately after mixing of the gel and increased by 3 pH units during the synthesis. During the first stage of the heating (25−85 °C), no change in pH was observed by using a conventional pH meter. During formation of the layered intermediate prephase (85−120 °C), the pH increased by ∼2 units. A second sharp pH increase was observed by in situ 13C NMR when the synthesis temperature approached 160−165 °C, which corresponded to the minimum temperature needed to prepare triclinic SAPO-34 within a reasonable time frame (a few days).

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