Organo-mineral nanohybrids. Incorporation, coordination and structuration role of acetone molecules in the tunnels of sepiolite

Abstract

The incorporation of acetone molecules inside the tunnels of sepiolite (SepSp-1) was monitored by a variety of techniques. By exposing sepiolite previously dehydrated at 120 °C for 20 h to acetone vapor at room temperature, acetone molecules incorporate into the tunnels of sepiolite in the minute timescale, form H-bonds with structural water, and restore the original structure of sepiolite. The characteristic signals of the ²⁹Si CP/MAS NMR spectrum of sepiolite are almost completely recovered in less than a minute. The TGA-DTA-MS results show that a large mass loss appears at 130 °C and a new mass loss appear at 380 °C for sepiolite previously heated at 120 °C for 20 h then exposed to acetone for a month. The mass loss at 130 °C is mainly accounted for by the release of structural water and a portion of the incorporated acetone. The mass loss at 380 °C is due to the release of the residue of acetone molecules that coordinate directly to terminal Mg(II) cations in the tunnels. The incorporation of acetone molecules inside the tunnels of sepiolite and its modifications upon thermal treatment were also studied by textural analysis, and ²⁹Si and ¹³C solid-state NMR techniques. A nanohybrid material with a structure similar to the parent sepiolite, is formed through the direct coordination of acetone molecules to the terminal Mg(II) cationic coordination. The coordinated acetone molecules stabilize the tunnel structure which collapses at a temperature much higher than in the case of the sepiolite mineral.