Action of silylating agents on a chrysotile surface and subsequent reactions with 2-pyridine and 2-thiophene carbaldehydes

Abstract

Chrysotile fibres have been modified in two distinct steps: first, the fibers were aminated with silylating agents such as 3-aminopropyltrimethoxysilane or N-[3-(trimethoxysilyl)propyl]ethylenediamine to give the products denoted CRI1 and CRI2, respectively. In the second step, these matrices reacted readily with 2-pyridine and 2-thiophene carbaldehydes to form C=N bonds, characteristic of a Schiff base. All immobilized materials were characterized by elemental analysis, IR spectroscopy, thermogravimetry, solid state ²⁹Si NMR, surface area measurements and X-ray diffractometry. Nitrogen elemental analysis indicated the presence of 1.20 and 2.87 mmol g^–1 of pendant groups on CRI1 and CRI2 surfaces, respectively. The experimental C/N ratios are 3.14, 2.90, 3.14 and 4.49 for modified materials CRI1L1, CRI1L2, CRI2L1 and CRI2L2, respectively. These results are in agreement with the yields of the successive reaction steps. The original chrysotile structure was maintained for the aminated modified surfaces. The surface area of prepared materials decreased with functionalization to values of <5.0 m² g^–1. All matrices obtained from reaction with aldehydes showed a C=N band at 1636 cm^–1, which is related to Schiff bond formation. Products derived from the reaction with pyridine carbaldehyde showed bands associated with aromatic and aliphatic C-H stretching bands at 3050 and 2930 cm^–1, respectively and pairs of bands at 1590, 1570 and 1470, 1436 cm^–1 are attributed to aromatic ν(C=C). These results indicate that the silylating agents are covalently bonded to the chrysotile surface.

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