| Abstract
| - The process of incorporation of pyridine in the nanostructured tunnels of sepiolite wasstudied in detail, using various complementary characterization techniques, microporosimetry, thermal gravimetric analysis, FTIR, and multinuclear solid-state NMR. It isdemonstrated that a remarkable nanohybrid material, SEP−PYR, is formed through thedirect coordination of pyridine to the edge Mg(II) sites of the tunnels. This material is formedat temperatures above 140 °C when the sepiolite tunnels are dehydrated and the pyridinemolecules are trapped in the tunnels. In a first step toward the formation of SEP−PYR, thepyridine molecules were incorporated at room temperature in the tunnels, by exposingsepiolite to pyridine vapors. The incorporated pyridine molecules are H-bound to thestructural water molecules coordinated to the edge Mg(II) cations. In a second step, uponheating to 140 °C, approximately 50% of the pyridine is lost, together with most of thestructural water coordinated to Mg(II). This event is accompanied by direct coordination ofthe remaining pyridine molecules in the tunnels to the edge Mg(II) ions of the octahedralsheets, resulting in a material with a structure similar to the parent sepiolite, but withpyridine molecules coordinated to the Mg(II) edge cations. This material is stable up to 450°C. At this temperature, the coordinated pyridine molecules escape from the tunnels, resultingin a collapsed sepiolite structure.
- This paper demonstrates by various convergent characterization methods that a remarkable nanohybrid material is formed through the direct coordination of pyridine to the edge Mg(II) sites of the nanostructured tunnels of sepiolite. This material, stable up to 450 °C, is formed at temperatures above 140 °C when the sepiolite tunnels are dehydrated and the pyridine molecules are sequestered in the tunnels. The structural stability of sepiolite is strongly increased upon direct Mg(II) coordination of pyridine.
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