Nanostructured Hybrid Materials Formed by Sequestration of Pyridine Molecules in the Tunnels of Sepiolite

Abstract

The process of incorporation of pyridine in the nanostructured tunnels of sepiolite was studied in detail, using various complementary characterization techniques, microporosimetry, thermal gravimetric analysis, FTIR, and multinuclear solid-state NMR. It is demonstrated that a remarkable nanohybrid material, SEP-PYR, is formed through the direct coordination of pyridine to the edge Mg(II) sites of the tunnels. This material is formed at temperatures above 140 °C when the sepiolite tunnels are dehydrated and the pyridine molecules are trapped in the tunnels. In a first step toward the formation of SEP-PYR, the pyridine molecules were incorporated at room temperature in the tunnels, by exposing sepiolite to pyridine vapors. The incorporated pyridine molecules are H-bound to the structural water molecules coordinated to the edge Mg(II) cations. In a second step, upon heating to 140 °C, approximately 50% of the pyridine is lost, together with most of the structural water coordinated to Mg(II). This event is accompanied by direct coordination of the remaining pyridine molecules in the tunnels to the edge Mg(II) ions of the octahedral sheets, resulting in a material with a structure similar to the parent sepiolite, but with pyridine 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, resulting in a collapsed sepiolite structure.

The Incorporation of Indigo Molecules in Sepiolite Tunnels

“…It should be stressed that the same behaviour was evident when small molecules, such as pyridine, were incorporated in the tunnels of sepiolite. [25] It is certain that molecules are located in the sepiolite tunnels. We must first show that these molecules are not zeolitic water blocked in the clay pores by indigo molecules located at the end of the fibres (Figure 1b).…”

“…[20,21] Gas molecules (CO 2 , O 2 , N 2 ) can replace this water inside the tunnels. [22] Analytical evidence, reported only recently, of small organic molecules (for example, pyridine derivatives, acetone, methanol [25][26][27] ) encapsulated in the tunnels with sepiolite as a matrix led to the announcement of the possible development of new, original nanocomposites. [23,24] More generally, considering the stable introduction of larger molecules, their location and their incorporation in tunnels are still largely controversial.…”

Nafion®–sepiolite composite membranes for improved proton exchange membrane fuel cell performance

“…As detailed by several authors [35,42], the heating of pristine sepiolite reveals a multi-step dehydration process, corresponding to the loss of zeolitic water first and then of coordinated water. The zeolitic water is lost in one step, between room temperature and 100 °C, while the coordinated water is lost in two steps, between 100 and 300 °C first and then between 300 and 600 °C.…”

Effect of reaction conditions on silanisation of sepiolite nanoparticles

“…The single particles of sepiolite, unlike other clays, have a needle-like morphology. [3,4] Due to the discontinuity in the external silica layer, a significant number of silanol (SiÀOH) groups exist on the surface of sepiolite. These groups can CONTACT Mohammad Atai m.atai@ippi.ac.ir attach to different pendant functional organosilyl groups, to form some organic characteristics to the precursor inorganic support.…”